Diabetes Prevention Program Outcomes Study
Phase: PHASE3
Conditions: Diabetes Mellitus, Cancer, CVD
Sponsor: National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK)

Version 4.4     May 22, 2019 
 
 
 
 
PROTOCOL 
 
for the 
 
DIABETES PREVENTION PROGRAM 
OUTCOMES STUDY  
 
(DPPOS) 
 
IND # 142797 
ClinicalTrials.gov # NCT00038727 
 
Diabetes Prevention Program Research Group 
 
Date: May 22, 2019 
 
 
Version 4.4 
 
Version 1.0 May 30, 2002 
Version 1.1 October 8, 2002 
Version 2.0 November 18, 2004 
Version 2.1 July 5, 2006 
Version 3.0 February 2, 2009 
Version 3.1 April 20, 2011 
Version 3.2 June 25, 2012 
Version 3.3 February 11, 2013 
Version 3.4 March 1, 2014 
Version 4.0 March 1, 2015 
Version 4.1 March 1, 2016 
Version 4.2 May 1, 2016 
Version 4.3 November 27, 2017 
 
 
Distributed by the DPPOS Coordinating Center 
Located at 
The Biostatistics Center 
The George Washington University 
6110 Executive Boulevard, Suite 750 
Rockville, Maryland 20852

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Rockville, Maryland 
 
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Table of Contents 
IND # 142797.................................................................................................................................................. 1 
1. 
EXECUTIVE SUMMARY .................................................................................................. 4 
1.1. 
Background ............................................................................................................................ 4 
1.2. 
Objectives ............................................................................................................................... 7 
1.3. 
Study Population .................................................................................................................... 7 
1.4. 
Study Interventions ................................................................................................................ 7 
1.5. 
Outcomes ................................................................................................................................ 8 
1.6. 
Design and Power ................................................................................................................... 9 
1.7. 
Analyses ............................................................................................................................... 10 
2. 
OBJECTIVES..................................................................................................................... 11 
2.1. 
Primary ................................................................................................................................. 11 
2.2. 
Secondary ............................................................................................................................. 11 
2.3. 
Other Objectives ................................................................................................................... 12 
3. 
BACKGROUND AND RATIONALE .............................................................................. 13 
3.1. 
The Diabetes Prevention Program (1996-2001) ................................................................... 13 
3.1.1. 
DPP Study Rationale and Design .......................................................................................... 13 
3.1.2. 
DPP Study Cohort ................................................................................................................. 14 
3.1.3. 
DPP Outcome Data ............................................................................................................... 14 
3.1.4. 
DPP Study Results ................................................................................................................. 16 
3.1.5. 
Bridge Period Between End of Masked Intervention and Initiation of DPPOS (2002) ......... 16 
3.2. 
The Diabetes Prevention Program Outcomes Study Phases 1&2 (DPPOS) (2002 – 2015) . 17 
3.2.1. 
DPPOS Study Rationale and Design ..................................................................................... 17 
3.2.2. 
DPPOS Study Cohort ............................................................................................................ 17 
3.2.3. 
DPPOS Phase 1 Results: Diabetes Prevention ..................................................................... 18 
3.2.4. 
DPPOS Phase 2 Results: Impact of DPP Interventions on Microvascular Disease ............. 19 
3.2.5. 
DPPOS Phase 1 & 2 Results: Impact of DPP Interventions on Cardiovascular Disease 
(CVD) Risk ........................................................................................................................... 20 
3.3. 
DPPOS Phase 3 (2015-2025) ............................................................................................... 21 
3.3.1. 
DPPOS Phase 3: Effects of metformin on CVD .................................................................... 22 
3.3.2. 
DPPOS Phase 3: Impact of DPP Interventions on Cancer ................................................... 23 
3.3.3. 
DPPOS Phase 3: Diabetes Outcomes ................................................................................... 24 
3.3.4. 
DPPOS Phase 3: Effects of Interventions on Microvascular Disease ................................... 24 
3.3.5. 
DPPOS Phase 3: Epidemiology of Microvascular Disease and Neuropathy in IGT and New-
onset Type 2 Diabetes........................................................................................................... 24 
3.3.6. 
DPPOS Phase 3: Epidemiology of CVD in IGT and New-onset Type 2 Diabetes ................ 25 
3.4. 
Other important DPP/DPPOS Analyses ............................................................................... 27 
3.4.1. 
Economic Implications .......................................................................................................... 27 
3.5. 
Effects of Race-ethnicity and Sex ........................................................................................ 27 
3.5.1. 
Risk Factors for Type 2 Diabetes and Diabetes-related Complications in Minority 
Populations .......................................................................................................................... 28 
4. 
DEFINITION OF OUTCOMES ....................................................................................... 30 
4.1. 
Primary Outcomes during DPP and DPPOS ........................................................................ 30 
4.1.1. 
Diabetes and Glycemia: OGTT and FPG ............................................................................. 30 
4.1.2. 
Composite Diabetes-related Microangiopathic and Neuropathic Outcome ......................... 31 
4.1.3. 
Cardiovascular Disease ........................................................................................................ 32 
4.1.4. 
Cancer ................................................................................................................................... 32 
4.1.5. 
Determining Vital Status and Cause of Death for Participants............................................. 33 
4.1.6. 
Medicare database ................................................................................................................ 33 
4.2. 
Other Secondary Outcomes .................................................................................................. 33 
4.2.1. 
Glycemia and insulin secretion: ............................................................................................ 33 

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4.2.2. 
Cardiovascular disease and risks, assessed by: .................................................................... 33 
4.2.3. 
Retinopathy, assessed by: ...................................................................................................... 34 
4.2.4. 
Nephropathy, assessed by: .................................................................................................... 34 
4.2.5. 
Neuropathy, assessed by: ...................................................................................................... 34 
4.2.6. 
Physical activity, nutrition, behavioral measurements, and body weight and obesity, 
assessed by: .......................................................................................................................... 34 
4.2.7. 
Health related quality of life, assessed by: ............................................................................ 34 
4.2.8. 
Resource Utilization, Costs, Health Utilities, and Effectiveness of treatments ..................... 35 
4.2.9. 
Safety tests: ............................................................................................................................ 35 
4.2.10. Serologic evidence of type 1 diabetes, assessed by: .............................................................. 35 
4.2.11. Stored specimens: .................................................................................................................. 35 
4.2.12. Other chemistries: ................................................................................................................. 36 
5. 
STUDY DESIGN ................................................................................................................ 37 
5.1. 
Overall Design...................................................................................................................... 37 
5.2. 
Participation Criteria ............................................................................................................ 38 
5.3. 
 Procedures for obtaining surrogate consent ......................................................................... 38 
5.4. 
Principles Guiding the Selection of a Study-wide Group Lifestyle Intervention ................. 38 
5.5. 
Masking ................................................................................................................................ 39 
6. 
PARTICIPANT MANAGEMENT PROTOCOLS ......................................................... 40 
6.1. 
Schedule of Follow-up Visits ............................................................................................... 40 
6.1.1. 
Interim Visits ......................................................................................................................... 40 
6.1.2. 
Confirmation (CON) Visits .................................................................................................... 40 
6.1.3. 
Suspension of Follow-up Visits .............................................................................................. 40 
6.1.4. 
Home or Telephone Visits...................................................................................................... 41 
6.1.5. 
Remote Visits ......................................................................................................................... 41 
6.1.6. 
Retention Monitoring and Recovery of Inactive Participants ............................................... 41 
6.2. 
Lifestyle Program in DPPOS Phases 1 & 2 .......................................................................... 42 
6.2.1. 
Lifestyle Resource Core and Lifestyle Advisory Group ......................................................... 42 
6.2.2. 
Staff for Lifestyle Interventions .............................................................................................. 42 
6.2.3. 
HELP Program ...................................................................................................................... 42 
6.2.4. 
Boost Lifestyle ....................................................................................................................... 43 
6.2.5. 
Indices of Adherence ............................................................................................................. 44 
6.3. 
Lifestyle Program in DPPOS Phase 3 .................................................................................. 44 
6.4. 
Metformin Pharmacological Treatment................................................................................ 44 
6.4.1. 
Description of Intervention .................................................................................................... 44 
6.4.2. 
Mechanism of Metformin Action ........................................................................................... 45 
6.4.3. 
Dosing Schedule and Restarts ............................................................................................... 45 
6.4.4. 
Safety Monitoring and Measures to Reduce and Manage Potentially Drug related side 
Effects ................................................................................................................................... 45 
6.4.5. 
Indices of Adherence ............................................................................................................. 48 
7. 
DEFINITION AND MANAGEMENT OF CONCOMITANT CONDITIONS ............ 49 
7.1. 
Pregnancy and Contraception ............................................................................................... 49 
7.1.1. 
Safety Monitoring .................................................................................................................. 49 
7.1.2. 
Use of Study Metformin During Pregnancy and Breast-feeding ........................................... 49 
7.1.3. 
Outcomes Assessment Following Pregnancy ........................................................................ 49 
7.2. 
Diabetes ................................................................................................................................ 50 
7.2.1. 
Interim Visits for Symptoms ................................................................................................... 50 
7.2.2. 
Intervention and Follow-up for Participants with Diabetes .................................................. 50 
8. 
ADVERSE EVENT REPORTING ................................................................................... 52 
8.1. 
Definitions ............................................................................................................................ 52 
8.2. 
Eliciting and Recording Serious Adverse Events ................................................................. 52 

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9. 
DATA PROCESSING ........................................................................................................ 53 
9.1. 
Data Forms ........................................................................................................................... 53 
9.1.1. 
Other Forms .......................................................................................................................... 53 
9.2. 
Data Entry and Management System ................................................................................... 54 
9.2.1. 
Clinical Centers ..................................................................................................................... 54 
9.2.2. 
Central Biochemistry Laboratory .......................................................................................... 55 
9.3. 
Centralized Data Management System ................................................................................ 55 
9.4. 
Performance Monitoring ...................................................................................................... 55 
9.4.1. 
Training Workshop and Site Visits ........................................................................................ 55 
9.5. 
Interim Statistical Reports .................................................................................................... 56 
10. 
STUDY ADMINISTRATION ........................................................................................... 57 
10.1. 
Organizational Units ............................................................................................................ 57 
10.1.1. Clinical Centers ..................................................................................................................... 57 
10.1.2. Coordinating Center .............................................................................................................. 57 
10.2. 
Funding Mechanism/Study Resources ................................................................................. 57 
10.3. 
Working Committees ........................................................................................................... 58 
10.3.1. Steering Committee and Subcommittees ................................................................................ 58 
10.3.2. Data and Safety Monitoring Board ....................................................................................... 58 
10.4. 
Policies ................................................................................................................................. 59 
10.4.1. Publications ........................................................................................................................... 59 
10.4.2. Ancillary Studies .................................................................................................................... 59 
11. 
STATISTICAL CONSIDERATIONS .............................................................................. 61 
11.1. 
Data Relevant to the Diabetes Outcome ............................................................................... 61 
11.2. 
Study Power ......................................................................................................................... 61 
11.2.1. Power for the Development of Diabetes ................................................................................ 61 
11.2.2. Power for the Microangiopathy Outcome, Year 11 ............................................................... 62 
11.2.3. Power for Cancer Development ............................................................................................ 62 
11.2.4. Power for CVD (MACE) Development .................................................................................. 62 
11.3. 
Analysis ................................................................................................................................ 63 
11.3.1. Analysis of Development of Diabetes .................................................................................... 63 
11.3.2. Composite Outcomes of Microangiopathic and Neuropathic Disease .................................. 64 
11.3.3. Analysis of Cancer and MACE Incidence.............................................................................. 64 
11.3.4. Secondary Research Questions ............................................................................................. 65 
11.4. 
Monitoring and Timing of Analyses .................................................................................... 66 
12. 
OUTCOMES SCHEDULE ................................................................................................ 67 
12.1. 
Visit Schedule ...................................................................................................................... 76 
13. 
STUDY TIMETABLE ....................................................................................................... 77 
14. 
BIBLIOGRAPHY .............................................................................................................. 79 
 
 

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1. 
EXECUTIVE SUMMARY 
 
1.1. 
Background 
 
Type 2 diabetes mellitus (T2DM) is rapidly becoming the most common chronic disease 
in the United States, with the most recent estimates of more than 9% of the adult population 
affected and 1,700,000 new cases per year.  T2DM is even more common in the elderly and in 
minority populations including African Americans, Hispanic Americans, Asian and Pacific 
Island Americans, and Native Americans.  In these populations, T2DM may be present in 10% to 
as much as 50% of the adult population.  Diabetes is accompanied by a multitude of severe long-
term complications that ultimately cause more adult cases of blindness, renal failure, and 
amputations than any other disease in the United States.  In addition, persons with T2DM have a 
2 to 4 fold increased risk for cardiovascular and peripheral vascular disease and stroke.  Owing 
largely to the high costs of caring for T2DM and its attendant long-term complications, total 
health care costs for diabetes have been estimated at approximately 245 billion dollars per year, 
or 12% of total U.S. health care expenditures in 2012.  The enormous human and financial costs 
that accompany T2DM, and the difficulty in treating it effectively once it has developed, make it 
an appropriate target for prevention.  
The Diabetes Prevention Program (DPP, 1994-2001) was a multicenter controlled 
clinical trial examining the efficacy of an intensive lifestyle intervention or metformin to prevent 
or delay the development of diabetes in a population selected to be at high risk due to the 
presence of impaired glucose tolerance (IGT).  Development of diabetes, defined by 1997 ADA 
criteria, was the primary outcome while cardiovascular disease and its risk factors were 
important secondary outcomes. The DPP began recruitment in mid-1996 and completed 
recruitment approximately three years later with a study cohort composed of 68% women, 45% 
minorities, and 20% > age 60. All 3,234 volunteers received standard lifestyle recommendations 
and were randomly assigned to one of three interventions: intensive lifestyle with the aim of 
losing and maintaining 7% weight loss and achieving ≥150 minutes per week of moderate 
intensity physical activity, metformin therapy with 850 mg twice per day, or placebo.  The 
troglitazone intervention in a fourth treatment arm (n=585) was discontinued in June 1998 
because of the potential risk for severe liver toxicity that became apparent after the DPP was 
initiated (Figure 1). 
The DPP had excellent retention, with >99% of the study cohort alive at study end and 
93% of annual visits completed.  In addition, the intensive lifestyle cohort achieved a mean 
weight loss of 7% (14.5 lb.) and 224 minutes per week of physical activity by the end of the 16-
session core curriculum (at approximately 6 months) and maintained a 5% weight loss (10.3 lb.) 
and 189 minutes of activity per week after a mean study duration of 2.8 years. Seventy-two 
percent of participants assigned to metformin and 80% of those assigned to placebo took at least 
80% of assigned medications during the study.  
On the basis of a statistically significant and clinically compelling decrease in the 
development of diabetes in the lifestyle intervention and metformin-treated groups (58% and 
31% reduction in hazards, respectively) compared with the placebo treated group, the DPP Data 
Monitoring Board and NIDDK ended the masked treatment phase of the study in August, 2001, 
one year earlier than originally planned.   

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At the end of the DPP all participants were offered a lifestyle modification program that 
incorporated the features of the original intensive lifestyle intervention, but was implemented in 
group sessions during a 4-6 month period. The participants originally assigned to metformin 
continued open-label metformin therapy, and those assigned to placebo-treatment stopped the 
placebo. 
The DPP addressed its primary objective, establishing the efficacy of lifestyle 
modification and metformin in decreasing the incidence of diabetes in an ethnically diverse 
population at high risk for an average of 2.8 years; however, many important issues remained 
unanswered. Specifically, whether the decrease in the development of diabetes can be sustained 
was unknown. Moreover, determining whether the delay or prevention of diabetes would 
translate into a decrease in retinopathy, nephropathy, neuropathy, and cardiovascular disease, all 
of which require more years to develop than the DPP period of study, was critical to establish the 
true impact of the DPP on public health.  
The long-term follow-up study of the DPP, entitled the Diabetes Prevention Program 
Outcomes Study (DPPOS, 2002-2015), was designed to take further advantage of the 
scientifically and clinically valuable cohort of DPP volunteers and the large volume of data 
collected during the study to address the issues above.  The highly compliant DPP cohort, 
including 45% minorities, is the largest IGT population ever studied.  Moreover, the large 
number of patients with new onset T2DM, carefully followed from near the time of their true 
onset, provides an unparalleled opportunity to study the clinical course of type 2 diabetes. 
More than 87% of the original surviving DPP cohort joined DPPOS. As of December, 
2014 and after 12 years of DPPOS and a mean of 16 years of combined DPP/DPPOS, 84% of 
the surviving DPPOS cohort continue to attend annual follow-up visits. Analyses performed 
after 11 years of DPPOS demonstrated a durable effect of diabetes prevention associated with 
the lifestyle and metformin interventions with 27 and 18% reductions in diabetes incidence, 
respectively, compared with the placebo group. Analyses through the first 6 years of DPPOS 
(Phase 1) revealed significant reductions from baseline in CVD risk factors in the lifestyle 
intervention group, with decreased utilization of glucose-lowering and lipid-lowering 
medications. Analyses following year 11 of DPPOS Phase 2 (2013) revealed no significant 
differences in the prevalence of the aggregate microvascular outcome, comprised of fundus 
photography measured retinopathy, nephropathy based on estimated glomerular filtration rate 
(eGFR) or increased albuminuria (≥30 mg albumin/g creatinine), or neuropathy detected by 
abnormal monofilament sensation, among the treatment groups; however, in a pre-specified 
analysis by sex, women had a 21 and 22% reduced risk of this outcome in the lifestyle group 
compared with the placebo and metformin groups, respectively. Moreover, among the 
participants who had not developed diabetes during DPP/DPPOS, the prevalence of the 
aggregate microvascular outcome was 28% lower compared with those who had developed 
diabetes. Protocol version 3.4 described the DPPOS including the revisions incorporated to 
complete the second phase of DPPOS, from 2009 to 2015 (Figure 1). 
The DPPOS Phase 3 (2015-2025) is a 10-year study divided into two 5-year funding 
periods as required by the NIH, and will focus primarily on the effects of randomized 
metformin therapy on CVD and cancer; the continued, even longer term effects of the original 
randomized therapies during DPP and DPPOS on selected microvascular complications; and on 
the clinical course of pre-diabetes and new onset diabetes. Since protocol version 3.4 only 
covers participant visits through DPPOS study year 13 (ending October 2015), version 4.0 adds 

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DPPOS study year 14-18 visits (through 2021), which will commence on July 1, 2015. Version 
4.0 covers the first 5-year period of DPPOS Phase 3.   
 
 
Figure 1. Timeline for DPP and DPPOS 
 
 

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1.2. 
 Objectives 
 
The primary objectives of DPPOS Phases 1 & 2 were to evaluate the long-term effects of 
active DPP interventions on the further development of diabetes and composite diabetes-related 
microvascular complications. DPPOS Phase 3 will evaluate the long-term effects of the original 
DPP/DPPOS interventions on cancer (first 5 years) and cardiovascular disease (second 5 years), 
with a particular focus on the effects of the metformin intervention. 
The secondary objectives of DPPOS Phase 3 are to evaluate the long-term effects of 
DPP interventions on the further development of diabetes, microvascular and selected health 
outcomes, the established and putative risk factors for those outcomes, and the costs and cost-
utility associated with delay or prevention of diabetes.  
Other research objectives include examining and comparing the incidence and 
determinants of these health outcomes in participants with new-onset diabetes and IGT, i.e. the 
clinical course of dysglycemia, as well as assessing subgroups of participants in order to evaluate 
the effect of race/ethnicity, age, and sex on health outcomes.  
1.3. 
 Study Population 
 
All surviving DPP participants, assigned to the original intensive lifestyle, metformin, 
troglitazone, and placebo groups, whether or not they developed diabetes during the DPP, were 
eligible and were invited to join DPPOS.  The former troglitazone participants were followed 
during Phase 1 of DPPOS, but no longer participate as research volunteers in the study.  At the 
time that DPPOS was initiated in September 2002, the mean age of the study population 
(including the former troglitazone participants) was 55 years, with 68% being women.  Fifty-five 
percent were Caucasian, 20% African-American, 16% Hispanic American, 5% American Indian, 
and 4% Asian or Pacific Islander-American.  A total of 2776 participants consented to participate 
in DPPOS (86.8% of the 3124 surviving participants).  Among intensive lifestyle, metformin, 
and placebo participants who joined DPPOS, 770 DPPOS participants had been diagnosed as 
having diabetes as of September, 2002. Through January 2015, an additional 824 DPPOS 
participants have developed diabetes, for a total of 1594 (56%) of DPPOS participants having 
developed diabetes. The mean age of the cohort as of January, 2015 was 66 years with 68% 
women, the same sex distribution as at DPP baseline.  
All surviving DPPOS participants will be invited to continue their participation in 
DPPOS Phase 3. For participants who can no longer sign informed consent owing to infirmity, 
alternate informed consent processes will be put into place according to local practice and 
institutional permission.  
 
1.4. 
 Study Interventions 
 
Quarterly lifestyle group sessions were held for all participants through summer 2014. 
These focused on lifestyle lectures as well as other topics of interest to participants with IGT or 
diabetes.  Additional group lifestyle boost sessions were offered to the group originally assigned 
to intensive lifestyle intervention through spring 2014.  During DPPOS Phase 3, an annual 
lifestyle check-up will be offered to the original lifestyle group. Open label metformin therapy 
(850 mg twice per day) will continue to be provided to the participants originally assigned to 
metformin.  An annual group lifestyle session will be held for all participants. 

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1.5. 
 Outcomes 
DPP 
The DPP was originally designed to examine the effects of lifestyle or metformin on 
diabetes development compared with placebo.  DPPOS was designed to assess the longer-term 
effects of the original DPP interventions on diabetes development and on diabetes complications 
and cost-effectiveness.  
 
DPPOS Phase 1 
The primary outcome for DPPOS Phase 1 was the same as the primary outcome during 
the DPP, i.e. development of diabetes according to American Diabetes Association criteria 
(fasting plasma glucose level ≥ 126 mg/dL [7.0 mmol/L] or 2-hour plasma glucose ≥ 200 mg/dL 
[11.1 mmol/L], after a 75 gram OGTT, and confirmed with a repeat test).   
 
DPPOS Phase 2 
The primary outcome for DPPOS Phase 2 was the prevalence of microvascular and 
neuropathic disease, defined as a composite of the following at the year 11 visit, or if the 
participant was deceased or lost to follow-up before year 11, as of his/her last assessment: 
a. Nephropathy: increased albuminuria (≥30 mg/gram creatinine, confirmed), or renal 
dysfunction (end-stage renal disease, dialysis or renal transplant) or eGFR < 45 ml 
per min based on serum creatinine, using the CKD-EPI equation or another validated 
algorithm; the qualifying criteria confirmed), or 
b. Retinopathy: retinopathy by fundus photography (ETDRS grade of 20 or greater) or 
adjudicated history of laser or other treatment for retinopathy, or 
c. Neuropathy: reduction or absence of light touch sensation to monofilament (Semmes-
Weinstein 10 gram) in either foot (< 8 of 10 applications detected). 
 
If a participant was taking antihypertensive drugs at the last assessment and did not meet 
the ACR or eGFR criteria at that time, he or she was considered to have reached the 
nephropathy outcome if the nephropathy criteria were met at 2 consecutive past visits. 
This substitutes for the occurrence of nephropathy at year 11. 
 
DPPOS Phase 3 
The primary outcome for DPPOS Phase 3 is time to the development of cancer and of 
major atherosclerotic cardiovascular events (MACE).  The cancer outcome includes the first 
occurrence of a new cancer diagnosed since DPP randomization and is the primary outcome 
during the first 5 years of DPPOS Phase 3, while MACE includes any of the following: nonfatal 
or fatal myocardial infarction or stroke or any cardiovascular death occurring since DPP 
randomization. The first occurrence of a new MACE event since DPP randomization is the 
primary outcome during the second 5 years of DPPOS Phase 3.  The occurrence of cancer and 
MACE events are collected at every visit using a standard medical history questionnaire and 
adjudicated by reviewers who are blinded to treatment assignment. 
 
SECONDARY OUTCOMES (outcomes assessed in Phases 1 & 2 but discontinued in DPPOS 
Phase 3 are shown in brackets) 
• Further development of diabetes  
• Diabetic retinopathy  

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• Diabetic neuropathy 
• Diabetic nephropathy  
• Cardiovascular disease events 
• [Subclinical atherosclerosis]  
• Risk factors for cardiovascular disease 
• Amputation in a lower extremity not resulting from major trauma 
• Hospitalizations  
• [Nutrition], Physical activity, body weight and obesity 
• [Dietary and exercise behaviors] 
• Physical functioning 
• Quality of life indices 
• Health care costs 
• Cognitive performance 
• Urinary incontinence 
• Sexual function 
• Pulmonary function 
• Bone density, whole body composition and vertebral fractures 
• Healthy Aging Index  
 
1.6. 
 Design and Power 
 
The power analysis at entry to DPPOS Phase 2 was as follows: based on the high rate of 
adherence during DPP and enrollment in DPPOS Phase 1, we estimated that 85% of all current 
(at the time) DPPOS participants would elect to continue in DPPOS Phase 2.  The global test 
provided 91% power for detecting a 25% reduction in microvascular complications due to 
intervention, from a projected placebo group average prevalence of 12.1% (each of 2 pair-wise 
comparisons, 2-sided, =0.025), and 74% power for a 20% reduction1,2. 
 
For DPPOS Phase 3, the analysis of cancer will take place at end of the first 5 years and 
of MACE after 10 years, using the log rank test.  To detect 28% risk reduction in total cancer 
associated with metformin, the study requires 170 events in the placebo group using a log-rank 
test with 85% power and 2-sided significance level of 0.05.  Assuming an increasing annual 
incidence rate of 1.86% by 2020 and an annual loss to follow-up of 1.04%, the projected 199 
cancer events in the placebo group will provide 89% power to detect a 28% hazard risk reduction 
at the end of the first 5-year period.  For MACE, we estimate an age related 2.1 fold increase in 
annual incidence rate in the next 10 years. This conservative increase is used to project events in 
the placebo participants of 116 and 156 after 5 and 10 additional years of DPPOS Phase 3 
assuming a 1.04% loss to follow-up per year. To detect a 30% hazard risk reduction in MACE 
incidence in the primary comparison of metformin and placebo with 85% power and a 2-sided 
significance level of 0.05 using a log-rank test, we require 145 placebo events. With the expected 
156 events in the placebo group by 2025, the study will have 89% power to detect a 30% hazard 
risk reduction.  This protocol represents 5 years of study although some of the goals described 
will require 10 total years of study. We hope to extend this protocol for an additional 5 years 
once the first 5-year period is completed.  
 

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1.7. 
 Analyses 
 
The primary outcome analysis in DPPOS Phase 1 compared the three intervention groups 
with regard to the cumulative incidence of diabetes. DPPOS Phase 2 compared the three 
intervention groups with respect to the DPPOS year 11 assessment of the components of the 
microangiopathy outcome using the global test1  The global test, which gives the component 
outcomes equal weight, is interpreted as testing for a consistent difference between groups across 
the component outcomes. 
The primary analysis for DPPOS Phase 3 will focus on the effects of metformin 
compared with placebo on the development of a number of diabetes related complications, 
including cancer and MACE. The primary and secondary outcome analyses will follow the 
“intention to treat” principle. The time to event analysis uses the date of event or first occurrence 
for composite outcomes.  A participant is considered “administratively censored” if he/she 
completes the full duration of follow-up without an event. Participants who died or prematurely 
discontinued follow-up visits prior to any event are “censored” as of their last follow-up visit or 
contact – hence, participants who did not enroll into DPPOS are censored as of their last contact 
during DPP. Separate Kaplan-Meier estimates of cumulative incidence curves are calculated for 
the three treatment groups and are compared using the log rank test3.  

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2. 
OBJECTIVES 
 
2.1. 
Primary  
 
The primary objective of DPPOS Phase 1 was to evaluate the long-term effects of active 
DPP interventions on the further development of diabetes. The primary objective of the DPPOS 
Phase 2 was to evaluate the long-term effects of the DPP interventions (Intensive Lifestyle and 
Metformin) on the prevalence of the composite diabetes-related microangiopathic and 
neuropathic outcome.   
The primary objective of the DPPOS Phase 3 is to evaluate the long-term effects of 
metformin compared with placebo on the incidence of cancer and of major atherosclerotic 
cardiovascular events (MACE: fatal and nonfatal myocardial infarction or stroke, and other 
cardiovascular deaths), with the comparisons of lifestyle compared with placebo, and lifestyle 
compared with metformin, important secondary objectives.  Major secondary comparisons will 
be lifestyle vs. placebo and metformin vs. lifestyle. 
 
2.2. 
Secondary 
 
The secondary objective of the DPPOS (DPPOS outcomes assessed in Phases 1 & 2 but 
discontinued in Phase 3 are shown in brackets) is to evaluate the long-term effects of DPP 
interventions on selected health outcomes including: 
• Further development of diabetes  
• Diabetic retinopathy 
• Diabetic neuropathy 
• Diabetic nephropathy  
• Cardiovascular disease events 
• [Subclinical atherosclerosis]  
• Risk factors for cardiovascular disease 
• Amputation in a lower extremity not resulting from major trauma 
• Hospitalizations  
• [Nutrition], Physical activity, body weight and obesity 
• [Dietary and exercise behaviors] 
• Physical functioning 
• Quality of life indices 
• Health care costs 
• Cognitive performance  
• Urinary incontinence 
• Sexual functioning  
• Pulmonary function  
• Bone density, whole body composition and vertebral fractures 
• Healthy Aging Index  
 
The outcomes chosen as secondary objectives were selected based on their clinical 
importance, demonstrated association with diabetes, and the possibility that they would be 
responsive to the DPP interventions. 

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2.3. 
Other Objectives 
 
Other research questions of the DPPOS Phase 3 include examining and comparing the 
incidence and determinants of these health outcomes in participants with new-onset diabetes and 
IGT, as well as assessing subgroups of participants in order to evaluate the effect of age, 
race/ethnicity, and sex on health outcomes.  
 
 

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3. 
BACKGROUND AND RATIONALE 
 
3.1. 
The Diabetes Prevention Program (1996-2001) 
 
3.1.1. DPP Study Rationale and Design 
 
The Diabetes Prevention Program (DPP) was a multicenter controlled clinical trial 
examining the efficacy of an intensive lifestyle intervention or metformin vs. placebo to prevent 
or delay the development of diabetes in a population selected to be at high risk due to the 
presence of impaired glucose tolerance (IGT)4-6.  Development of diabetes, defined by 1997 
ADA criteria, was the primary outcome while cardiovascular disease (CVD) and its risk factors 
were important secondary outcomes.  The original study design included four treatment arms: 
intensive lifestyle (ILS) intervention, troglitazone (TRO) treatment (400 mg/day), metformin 
(MET) treatment (850 mg twice per day), or placebo (PLB).  All medication-treated subjects 
received identical appearing coded medications, and treatment was double blind.  Troglitazone 
treatment was stopped in June 1998, owing to the accumulating evidence that troglitazone was 
responsible for rare, but potentially severe idiosyncratic liver toxicity.  The volunteers assigned 
to troglitazone therapy were offered a modified lifestyle intervention and continue to be followed 
as a separate group in the DPP. 
The original rationale for a study to prevent or delay diabetes was the following: 1. 
Diabetes mellitus, and in particular Type 2 diabetes (T2DM), had become epidemic in the US, 
currently affecting >9% of the adult population and with almost 1,700,000 new cases per year7. 
2. The consequences of T2DM including diabetes-specific complications, such as retinopathy, 
nephropathy, and neuropathy, and cardiovascular disease, cause severe morbidity and mortality 
with enormous human and financial costs8. 3. Although therapies to treat diabetes once it 
develops were available, the complex medical regimens required were difficult and costly to 
apply and many patients failed to achieve the glycemic levels and other treatment goals required 
to prevent or delay the long-term complications6.  4. A pre-diabetic state was well recognized, 
and could be identified with relatively simple screening methods, providing the opportunity of 
identifying persons at high risk for diabetes9, and, finally, 5. Potentially modifiable 
environmental factors, such as overweight and a sedentary lifestyle, that were known to increase 
risk for diabetes10-12, and medications that ameliorate hyperglycemia had been identified.  In 
concert, these factors suggested that interventions with the potential to prevent or delay the 
development of diabetes could be applied in persons identified at high risk to develop diabetes 
mellitus, a common chronic disease with grave long-term consequences. 
The DPP was designed with the expectation that prevention or delay of diabetes would 
ultimately prevent or delay the development of long-term, duration dependent diabetes-specific 
complications.  In addition, prevention or amelioration of CVD and/or CVD risk factors was 
predicted to manifest as a benefit of diabetes prevention interventions.  Accomplishing either of 
these aims would provide a major benefit with regard to long-term health by virtue of decreasing 
morbidity and mortality.  However, the duration of the DPP, planned as a 3-6 year study, did not 
allow an examination of whether “prevention” or delay of diabetes would translate into a 
reduction of clinical outcomes that usually require a longer period of time to develop.  Thus, the 
DPP was designed on the basis of power calculations directed at diabetes prevention4.  The 
ability to demonstrate a reduction in microvascular complications or “hard” CVD outcomes was 

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acknowledged from the outset to be limited.  Instead, changes in CVD risk factors and measures 
of atherosclerosis, such as ankle/brachial index, were collected. 
 
3.1.2. DPP Study Cohort  
 
The DPP recruited its study cohort between June 1996 and 1999, screening more than 
150,000 self-referred individuals.  Oral glucose tolerance testing (75 grams) was performed in 
approximately 20,000 persons to select high-risk individuals with impaired glucose tolerance 
(IGT) with two-hour plasma glucose values 140-199 mg/dL.  The eligibility criteria also required 
a fasting glucose level of 95-125 mg/dL, representing approximately the upper half of the IGT 
population.  Based on previous epidemiological studies, this population was projected to have a 
rate of progressing to diabetes of 7.5% per year4,9. The baseline characteristics of the study 
population have been described in detail5. (Table 1)  
At the time of the analysis of study end data (visits completed as of April 1, 2001), total 
study exposure was a mean of 2.8 years (range 1.8 to 4.6) with a total of ≈10,000 patient years in 
the 3,234 volunteers in the 3-arm study.  (See Table 1 for Baseline Characteristics of DPP 
Cohort)  An additional ≈2,000 years of follow-up data had been collected in the approximately 
550 volunteers in the ex-troglitazone treated group.  Finally, 623 members of the DPP cohort 
developed diabetes during the course of DPP, with the expectation that more would develop 
diabetes over time9. The date of diabetes onset is known within 6 months of its actual 
occurrence, due to repeat glucose testing throughout the trial. 
 
Table 1. Baseline Characteristics of DPP Cohort  
 
 
Overall 
Lifestyle 
Metformin 
Placebo 
N 
3234 
1079 
1073 
1082 
Age (yr) 
51 ± 11 
51 ± 11 
51 ± 10 
51 ± 10 
Sex: 
 
 
 
 
       Male 
1043 (32%) 
345 (32%) 
363 (34%) 
335 (31%) 
       Female 
2191 (68%) 
734 (68%) 
710 (66%) 
747 (69%) 
Race/ethnicity: 
 
 
 
 
     Caucasian 
1768 (55%) 
580 (54%) 
602 (56%) 
586 (54%) 
     African American                   
645 (20%) 
204 (19%) 
221 (21%) 
221 (20%) 
     Hispanic 
508 (16%) 
178 (17%) 
162 (15%) 
168 (16%) 
     American Indian 
171 (5%) 
60 (6%) 
52 (5%) 
59 (6%) 
     Asian American 
142 (4%) 
57 (5%) 
36 (3%) 
49 (5%) 
Fasting glucose (mmo1/L) 
5.9 ± 0.5 
5.9 ± 0. 5 
5.9 ± 0. 5 
5.9 ± 0. 5 
BMI (kg/m²) 
34 ± 7 
34 ± 7 
34 ± 7 
34 ± 7 
Blood pressure (mmHg) 
 
 
 
 
     Systolic 
124 ± 15 
124 ± 15 
124 ± 15 
124 ± 14 
     Diastolic 
78 ± 9 
79 ± 9 
78 ± 10 
78 ± 9 
From Diabetes Care 2000; 23:1619-29 (3). Data are means ± SD or n (%) unless otherwise stated.  Percentages may not add up to 100 because of 
rounding. 
 
 
3.1.3. DPP Outcome Data  
 
Study data included: measurements of glycemia, including mid-year or annual fasting and 
OGTT glucose values and HbA1c levels; measurements of insulin and proinsulin to help 
determine underlying causes of decline in glucose tolerance and as putative risk factors for CVD; 

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demographic and clinical variables that reflect risk for diabetes and/or CVD such as body mass 
index, weight distribution, direct measures of fat mass/distribution (CT scans on a sample), blood 
pressure, lipids; biochemical measures that are established or putative risk factors for the 
development of CVD including hemorheological factors; clinical CVD events categorized and 
adjudicated in a similar fashion to other interventional and epidemiological studies; and 
measures of atherosclerosis such as ankle/brachial index measured by Doppler and carotid 
intimal-medial thickness (IMT) measured by B-mode ultrasonography.  Finally, the DPP has 
stored samples that are suitable for analysis of other putative risk factors or mediators of diabetes 
or CVD that were not known or could not be afforded during the study.  Samples suitable for 
genetic analysis have also been collected, and have been analyzed as part of a separately funded 
affiliated project. In addition, samples have been kept in long-term storage for participants who 
consented to this.  All data collected include standardized measurements using uniform methods 
and central analysis/reading/grading with easily accessible stored data. Data and samples have 
been provided to the NIDDK repository and thereby made available to the broader scientific 
community. 
 
 
Figure 2: Life-table Analysis of Cumulative Incidence of Diabetes 
Development During DPP 
 
 
 
0   
0.5    
1 
1.5     
2  
2.5        3  
3.5        4   
Years from randomization
40
30
20
10
0
Cumulative incidence (%)
Placebo
Metformin
Lifestyle
Time to diabetes

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3.1.4. DPP Study Results 
 
After approximately 2.8 years of mean study time, the external Data Monitoring Board and 
sponsoring institute, the NIDDK, concluded that the DPP had convincingly demonstrated that the 
intensive lifestyle intervention and metformin therapy decreased the development of diabetes.  
Compared with placebo, intensive lifestyle and metformin reduced the development of diabetes 
by 58% and 31% risk reduction, respectively (Table 2, Figure 2).  Both results were significant 
and lifestyle was significantly more effective than metformin6. The therapies were effective 
across all ethnic and racial groups and in men and women.  The intensive lifestyle intervention 
cohort achieved the target goal of 7% mean weight loss and at least 150 min of activity per week 
at year 1.  The DPP cohort proved to be remarkably compliant, with 94% retention of volunteers 
over time, and completion of > 90% of study requirements.  Adherence (>80% of assigned 
medication) to metformin was 72%.  
 
Table 2. Summary of Outcomes During DPP 
 
*Values are mean percent weight loss (standard error) 
3.1.5. Bridge Period Between End of Masked Intervention and Initiation of DPPOS (2002) 
 
The DPP Research Group decided before the study results were known, to offer effective 
therapy to the cohort at study end, should one of the study interventions prove to be effective.  
This decision was made not from any scientific imperative, but based on the sense of the DPP 
Research Group and NIDDK that initiating effective therapy was consistent with our obligation 
to the participants who had made the DPP possible.  During the final six months of the DPP 
(January – June 2002), under a “bridge” protocol, all participants were offered an intensive 
Lifestyle program with the same goals used in the DPP, but offered in a group setting, rather than 
an individual setting.  In addition, during this period, the former ILS group was offered 
continued ILS, albeit with a less frequent contact than during the DPP.  Placebo therapy was 
stopped after individual unmasking took place between August and November 2001.  Metformin 
was continued during this period, with participants and staff unmasked to treatment assignment. 
 
 
Placebo 
Metformin 
Lifestyle 
Development of diabetes (percent per 
year) 
11 
7.8 
4.8 
Reduction of diabetes compared with 
placebo (%) 
 
31 
58 
Number needed to treat to prevent 1 
case in 3 years 
 
13.9 
6.9 
Weight loss (%)* 
 
 
 
Year 1 
0.43 (0.5) 
2.72 (2.9) 
6.7 ( 7.2) 
Year 2 
0.06 (0.1) 
2.07 (2.2) 
5.4 (5.7) 
Year 3 
-0.37 (0.4) 
1.18 (1.3) 
4.7 (5.0) 
Leisure Activity (Met-hours /wk) 
 
 
 
1 year 
4.46 
4.92 
5.57 
2 year 
4.61 
4.37 
5.27 
3 year 
4.95 
4.29 
5.08 

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3.2. 
The Diabetes Prevention Program Outcomes Study Phases 1&2 (DPPOS) (2002 – 
2015) 
 
3.2.1. DPPOS Study Rationale and Design 
 
The DPP was designed to ascertain whether metformin treatment and/or intensive 
lifestyle modification reduced the development of diabetes, compared with placebo, in subjects 
with IGT during a period of intervention averaging 4 years. Owing to the large and statistically 
significant reduction in development of diabetes in the lifestyle intervention group (58%) and in 
the metformin-treated group (31%), compared with placebo treatment, the DPP was ended, by 
consensus of the external Data Monitoring Board, NIDDK, and the Study Group, approximately 
one year earlier than planned (Figure 2).  The prevention – or delay - of diabetes should be 
associated over time with a reduced rate of diabetes-related clinical events, namely diabetic 
microangiopathy and neuropathy and cardiovascular disease (CVD).  The relatively brief study 
period of the DPP, with a mean follow-up of 2.8 years (range 1.8-4.8 years), precluded an 
examination of the long-term clinical impact of diabetes prevention.  An appreciation of the 
long-term clinical impact of diabetes prevention is critical in order to understand the role of the 
DPP interventions in improving health.  Moreover, the long-term epidemiological follow-up of 
the DPP cohort would increase our understanding of the clinical course of IGT and new-onset 
type 2 diabetes. 
 
3.2.2. DPPOS Study Cohort 
All surviving participants from DPP were invited to join DPPOS.  Of the 3,234 three-arm 
participants randomized to DPP, 68 withdrew during DPP, and 39 died before they could enroll 
in DPPOS.  Of the remaining 3,127 DPP participants, 351 did not enroll in DPPOS or could not 
be contacted, and 2,776 (88.8%) enrolled.  The characteristics of the DPPOS cohort at 
randomization, DPP end, and at DPPOS Phase 2 end (2013), which will serve as baseline for 
DPPOS Phase 3, are shown in Table 3.  
 
 
Table 3 Characteristics (means) of DPPOS Cohort at randomization, DPP end and DPPOS Phase 2 end 
 
DPP 
DPP End (2001)* 
DPPOS Phase 2 End (2013)** 
 
Total- 
2776 
PLB- 
935 
MET-
926 
ILS-915 
PLB - 
780 
MET - 
772 
ILS - 
751 
Non-DM-
1226 
DM-1550 
Age (yr) 
51 
54 
54 
54 
65 
66† 
66 
67 
65§ 
Sex (% women) 
68 
69 
67 
68 
69 
68 
68 
68 
68 
Diabetes (%) 
0 
30 
21 
14 
60 
55 
52 
0 
100 
BMI (kg/m2) 
34 
34 
33† 
32†‡ 
33 
32† 
32† 
31 
33§ 
HbA1c (%) 
5.9 
6.1 
6.0† 
5.9†‡ 
6.3 
6.1† 
6.2‡ 
5.6 
6.6§ 
SBP (mmHg) 
124 
123 
123 
120†‡ 
121 
122 
121 
121 
122 
DBP (mmHg) 
78 
76 
76 
74†‡ 
71 
71 
71 
71 
71 
LDL-C (mg/dL) 
125 
124 
123 
124 
96 
95 
98 
102 
92§ 
HDL-C (mg/dL) 
46 
45 
47† 
47† 
53 
55† 
54 
56 
52§ 
Triglycerides (mg/dL) 
162 
157 
153 
138†‡ 
137 
137 
130 
118 
147§ 
Baseline characteristics did not differ across treatment groups except for HDL. Treatment group differences († significant vs PLB, ‡ significant vs MET) in means; at 
study end by glycemic status with significant glycemic differences noted (§significant vs non-DM) *Final DPP annual visit during masked phase; **DPPOS year 11 
annual visit. 
 
 
 
 

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3.2.3. DPPOS Phase 1 Results: Diabetes Prevention 
 
The first question addressed in the DPPOS was the long-term impact of the DPP interventions on 
the development of diabetes. This effect of the DPP interventions was evaluated in two ~6-year 
phases during DPPOS. After ~6 years of DPPOS (DPPOS Phase 1, ~10 years after 
randomization), weight regain was evident in the group originally assigned to ILS and a 
persistent modest weight loss was seen in the group originally assigned to MET. In the cohort 
followed into the DPPOS, diabetes incidence rates during DPP were 4.8 (95% CI 4.1, 5.7) cases 
per 100 person-years (P-Y) in ILS, 7.8 (6.8, 8.8) in MET and 11.0 (9.8, 12.3) in PLB (Figure 3). 
Although the rates of diabetes development in the DPPOS period became similar across 
treatment groups: 5.9 (5.1, 6.8) per 100 P-Y in ILS, 4.9 (4.2, 5.7) in MET, and 5.6 (4.8, 6.5) in 
PLB, the between-group differences established during the DPP interval produced persistent 
treatment-related differences in diabetes incidence at 10 years (35% reduced ILS vs PLB and 
18% reduced MET vs PLB)13. This pattern persisted into the second phase of DPPOS (Phase 2, 
years 10-15 following randomization). At year 15 (the end of DPPOS Phase 2), cumulative 
diabetes incidence was 52% of those originally assigned to ILS, 55% of those originally assigned 
to MET and 60% of those originally assigned to PLB. (Figure 3) 
 
Figure 3. Diabetes outcomes in the DPP and DPPOS 
 
Of note, the diabetes ascertainment methods employed in the DPP/DPPOS identify the 
transition to diabetes at an earlier stage than is seen in traditional clinical care. The mean fasting 

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glucose in the study groups at Year 15 was 122 (ILS), 118 (MET) and 123 mg/dl (PLB), and the 
mean HbA1c was 6.2% (ILS), 6.1% (MET) and 6.3% (PLB). This indicates that the magnitude 
and duration of exposure to dysglycemia, and to overtly diabetic levels of elevated glucose, are 
less than would be predicted despite the majority of each group having made the transition to 
biochemically diagnosed diabetes.  
 
3.2.4. DPPOS Phase 2 Results: Impact of DPP Interventions on Microvascular Disease 
 
The second question addressed in DPPOS Phase 2 was the long-term clinical impact of 
having prevented or delayed the onset of diabetes, specifically the effects of DPP interventions 
on diabetes-related complications.  The ultimate health care benefit of diabetes “prevention” was 
expected to be a function of the time period during which diabetes is delayed, and whether and to 
what extent organ damage can be prevented or delayed.  Epidemiological data suggest that 
prevention or delay of diabetes should result in less disease over time, but very few studies have 
been able to address this critical public health question directly.   
The development of diabetic retinopathy, nephropathy and neuropathy is believed to 
require chronic exposure to levels of glycemia at or above the diagnostic limits for diabetes14. 
Thus, based on conventional thinking, the appearance of these complications in DPP participants 
was expected to be restricted to those who develop diabetes, and was expected to occur only 
some years after biochemical conversion.  The decreased development of diabetes with intensive 
lifestyle and metformin was therefore expected to reduce the frequency and extent of these 
disease entities compared with their occurrence in the former placebo-treated group.  
For this set of analyses the pre-specified primary outcome was an aggregate of 
microvascular diseases, defined as the presence of one or more of nephropathy, retinopathy or 
neuropathy. Nephropathy was defined as albuminuria ≥30 mg/g creatinine in a spot urine 
collection on 2 consecutive tests or an estimated eGFR <45 ml/min/1.73 m2, based on annual 
serum creatinine using the CKD-EPI equation15 on 2 consecutive tests, or renal failure (end-stage 
renal disease, dialysis or transplantation). Participants taking antihypertensive drugs at the final 
assessment who did not meet albuminuria or eGFR criteria at that time were considered to have 
reached the nephropathy outcome if the nephropathy criteria were met at 2 consecutive past 
visits. Retinopathy was diagnosed on 7-field stereoscopic fundus photography as an ETDRS 
grade 20 or greater16 in either eye or treatment of retinopathy with laser or intravitreal injections.  
The presence of neuropathy was based on loss of light touch sensation (<8 of 10 applications 
detected on the dorsum of the great toe) measured with a 10-gram Semmes-Weinstein 
monofilament17.  Kidney function and neuropathy were measured annually during DPPOS, while 
retinopathy was measured during the final year of DPPOS (2012-13). The study was powered 
based on the global test1 at 91% power to detect a 25% reduction in microvascular complications 
due to an intervention, from a projected placebo group average prevalence of 12.1% (powered 
for each pair-wise comparison, 2-sided, α=0.025)2. 
Despite the group differences in diabetes incidence, the average prevalence of the 
microvascular outcomes at DPPOS Phase 2 end did not differ significantly among the three 
treatment groups (Figure 4)18. We did observe some differences in complication prevalence in 
subgroup analyses. The prevalence of the microvascular outcome was approximately 50% higher 
in men than women, and increased with increasing age, but was similar across racial/ethnic 
groups.  The pre-specified sex-specific analysis showed a significant sex-by-lifestyle vs. placebo 
treatment interaction (P=0.047). In women but not in men, lifestyle intervention reduced 

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microvascular disease by 21% compared with placebo (P=0.03) and 22% (P=0.02) compared 
with metformin.  Participants who did not develop diabetes during DPP/DPPOS had a 28% 
lower aggregate microvascular disease prevalence at year 15 than those who did develop 
diabetes (P<0.001) for all treatment groups combined, with similar patterns in each treatment 
group (P=0.20 comparing treatment groups).   
 
 
Figure 4. The left panel presents the results for the prespecified aggregate result, and for 
the treatment effects within each type of microvascular complication. The right panel 
presents the results for the aggregate result, divided by major groupings. 
 
We observed the expected relationship of duration of diabetes, and exposure to 
hyperglycemia, with retinopathy and nephropathy, but not with neuropathy. Even 15 years after 
original randomization in the DPP, the differences in magnitude of hyperglycemia and duration 
of diabetes between treatment groups were modest. Further follow-up is needed to identify 
whether DPP treatments that prevent/delay the progression to diabetes, and the early and 
continuing glycemic separation of treatment groups, will produce a measurable beneficial effect 
on microvascular disease. 
 
3.2.5. DPPOS Phase 1 & 2 Results: Impact of DPP Interventions on Cardiovascular 
Disease (CVD) Risk 
 
Diabetes is estimated to account for as much as 25% of all cases of CVD19. With the 
T2DM epidemic, the absolute number of cases and the fraction attributable to T2DM will only 
grow. A decreased incidence of T2DM would be expected to decrease subsequent CVD; 
however, whether T2DM prevention reduces CVD is unknown.  Similarly, whether ILS or MET 
has direct preventive effects on the development of CVD in addition to, or independent of, their 
beneficial effects on T2DM development is unknown.  
Metformin has been beneficial in several small prevention trials of CVD in persons with 
diabetes20-23. In addition, metformin reduces myocardial infarct size, prevents heart failure and 
improves cardiac function in animal models24,25.  Evidence of beneficial effects on CVD risk 
factors and cardiac function independent of its antihyperglycemic action26, combined with the 
DPP-based recommendation for its use in prediabetes27,28, has led to recent CVD prevention 
studies with metformin in non-diabetic cohorts. The first of such studies found no benefit of 
metformin on carotid intimal media thickness change in patients with coronary heart disease 
(CHD)29.  Another showed no effects on left ventricular function30. A larger trial with clinical 
outcomes is in progress31.    

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The only published data on the long-term effects on CVD events of lifestyle interventions 
that target T2DM prevention come from the Da Qing study which recently reported a significant 
reduction in mortality, largely cardiovascular in origin, after 23 years of total follow-up, between 
their original control and lifestyle intervention groups32. These findings, although intriguing, 
must be viewed with skepticism because of the cluster (clinic-based) randomization, asymmetric 
loss-to-follow-up, and differences in age and smoking patterns in the two intervention groups. 
The recently completed Look AHEAD study, which used the DPP ILS in patients with ~ 8 years 
T2DM duration, showed no significant effects on the primary CVD outcome over ~12 years of 
follow-up33. The differences between Da Qing and Look AHEAD results suggest that lifestyle 
interventions may need to be started early in the course of dysglycemia. 
 
Table 4. CVD Risk Factors during DPP-Mean Change from Baseline 
 
CVD Risk Factors 
Placebo 
Metformin 
Lifestyle 
Blood pressure (mmHg) 
 
 
 
    Systolic 
-0.77 
-1.12 
-3.26 
    Diastolic 
-0.74 
-0.86 
-3.27 
Lipoproteins (mg/dL) 
 
 
 
    Total cholesterol 
-3.26 
-4.72 
-8.14 
    Triglycerides 
-3.39 
-3.04 
-21.98 
    LDL-cholesterol 
-1.37 
-4.00 
-4.37 
    HDL-cholesterol 
-.27 
0.39 
0.69 
Insulin level (U/ml) 
 
 
 
    Fasting 
0.74 
-2.93 
-4.52 
    30 min Post-OGTT 
1.45 
-6.92 
-13.49 
 
 
The DPP and DPPOS Phases 1 & 2 had insufficient power to detect an effect of the two 
active DPP interventions on CVD events owing to the relatively low rate of CVD events during 
the study.  Although the low event rates of major CVD precluded demonstrating a difference in 
event rates between the treatment groups, CVD risk factors were variably affected by the 
different DPP interventions.  (Table 4)  Blood pressure was significantly lower, lipid levels were 
less atherogenic, and insulin levels were lower in the Lifestyle treatment group, and to a lesser 
extent with metformin therapy, than in the placebo group. Longer follow-up of the DPP cohort 
will be highly informative regarding the effects of therapy on clinical outcomes that are likely to 
take longer to observe than the initial ~15 years of the DPP/DPPOS Phases 1 & 2. Continuation 
of the study in DPPOS Phase 3 presents the unique opportunity to evaluate the effects of MET 
begun during pre-diabetes vs PLB or ILS on CVD, the effects of ILS on CVD, and associations 
between T2DM prevention and CVD.  
 
3.3. 
DPPOS Phase 3 (2015-2025)  
 
 
There is a strong rationale for continued follow-up of the DPP/DPPOS cohort. The 
randomized study assignments at baseline provide a unique opportunity to evaluate metformin’s 
putative effects on CVD and cancer outcomes, which have been proposed in recent years. More 
generally, the random assignments allow long-term prospective intention-to-treat analyses.  The 
population has been highly adherent to study procedures and study therapies, and between-group 
differences in glycemia persist over time prompting projections of between-group differences in 
outcomes based on diabetes status and on total glycemic exposure. 

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Long-term follow-up of randomized controlled clinical trials has been highly informative 
in several completed clinical trials; e.g., the DCCT (EDIC)34, the Coronary Drug Project35,36 and 
4S37. This approach is predicated on the notion that the study intervention influences certain 
chronic disease processes in a manner that takes more time to manifest than the duration of the 
treatment being studied.  One of the best examples of such a study was the Coronary Drug 
Project, in which coronary and all-cause mortality were not altered at the completion of a 6-year 
period of niacin therapy even though cholesterol levels were significantly lowered35.  However, 
these clinical outcomes were significantly reduced after 9 years of further observational follow-
up38. The ongoing EDIC follow-up of the DCCT cohort demonstrated widening differences in 
outcomes as early as 4 years after the termination of assigned therapies34.  In addition, longer 
follow-up demonstrated differences in more advanced and costly complications, including the 
need for laser therapy for proliferative retinopathy, atherosclerosis and CVD events, between the 
treatment groups that were not apparent at the end of the DCCT11,34,39,40. Lastly, evaluation of the 
United Kingdom Prospective Diabetes Study (UKPDS) cohort 10 years following completion of 
the intervention phase of the study demonstrated significant differences in a number of outcomes 
in subjects previously randomized to the intensive and conventional treatment arms20.  Notably, 
despite glucose control not differing between the subjects following completion of the 
intervention, in those who had received the intensive glucose-lowering regimen, continued 
significant reductions in risk were observed in any diabetes-related outcome and microvascular 
complications and a significant reduction in risk became apparent for myocardial infarction and 
all-cause mortality. 
 
3.3.1. DPPOS Phase 3: Effects of metformin on CVD 
In DPP/DPPOS, intensive lifestyle and metformin reduced body weight and improved 
insulin resistance, glycemia and cardiometabolic vascular risk factors13,41-44.  However, whether 
T2DM prevention reduces CVD has not been shown.  More specifically, whether metformin has 
direct preventive effects on the development of CVD in addition to, or independent of, the 
beneficial effects on T2DM development is unknown. In DPPOS Phase 3 we will study the 
comparative effectiveness of the early initiation of metformin during pre-diabetes vs treatment 
only after the development of T2DM on CVD prevention. 
Metformin has been beneficial in several small prevention trials of CVD in T2DM, 
including in the UKPDS22,45. In addition, metformin reduces myocardial infarct size, prevents 
heart failure and improves cardiac function in animal models and human studies24,25.  Evidence 
of beneficial effects on CVD risk factors and cardiac function independent of its 
antihyperglycemic action26, combined with the DPP-based recommendation for its use in pre-
diabetes28, has led to recent studies with metformin for CVD prevention in non-diabetic cohorts. 
The first of such studies found no benefit of metformin on carotid intimal media thickness 
change in patients with CHD29 and a recent trial of metformin in non-diabetic patients showed no 
effects on left ventricular function30.   
DPPOS is by far the largest of the diabetes prevention studies with a cohort randomly 
assigned to metformin. Further, the long-term exposure to metformin beginning in pre-diabetes is 
a unique strength of this study. Although subjects in the other treatment groups can initiate 
metformin treatment once diagnosed with diabetes, the mean cumulative metformin exposure is 
currently 10.9, 2.4 and 1.8 y in MET, PLB and ILS. Further, 70% of the MET group subjects 
who have not developed T2DM continue to take study-related metformin. Projected cumulative 
metformin exposure will remain considerably greater in MET by virtue of its early randomized 

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use. DPPOS Phase 3 will also ascertain whether total years of metformin exposure, much of it 
during the period of prediabetes, reduces CVD risk.   
Although this phase of the study is focused on comparisons of metformin versus placebo 
treatment groups, we remain interested in the effects of diabetes prevention via the intensive 
lifestyle intervention. As noted above, the apparent differences between Da Qing and Look 
AHEAD results using lifestyle interventions to reduce the incidence of CVD suggest that 
lifestyle interventions may need to be started early in the course of dysglycemia to reduce long-
term CVD. This is a question we will be able to address in DPPOS Phase 3. 
In summary, further follow-up of DPPOS presents the unique opportunity to evaluate the 
effects of metformin begun during pre-diabetes vs PLB or ILS on CVD, the effects of ILS on 
CVD, and associations between T2DM prevention and CVD.  
 
3.3.2. DPPOS Phase 3: Impact of DPP Interventions on Cancer  
 
A focus on cancer is new for DPPOS Phase 3. The randomized metformin exposure 
beginning at DPP enrollment presents an unparalleled opportunity to address the putative 
beneficial effects of metformin on cancer in obese dysglycemic individuals. Accumulating 
epidemiologic evidence suggests that cancer risk is increased in overweight and obese 
individuals, with excess body weight accounting for 25-50% of cases of some common cancers 
(breast, colorectal, endometrial, renal cell, esophageal)46 The underlying mechanisms are 
unclear, but may involve obesity-associated hyperinsulinemia or increased IGF-147,48.  T2DM 
also increases the risk of several common cancers (hazard ratios 1.2 to 2.1), although it is not 
clearly established if this risk is independent of obesity49-51.  Little is known about whether 
lifestyle change (in particular, dietary weight loss interventions) for obesity or T2DM prevention 
can reduce cancer incidence.  Metformin has recently received attention as a potential anti-cancer 
agent, based on promising experimental and epidemiologic data52,53.  A recent meta-analysis of 
11 observational studies showed a 33% reduction in cancer incidence in patients taking 
metformin compared with other anti-diabetic drugs, and a 34% reduction in cancer mortality54.  
However, whether metformin has direct preventive effects on the development of cancer in 
addition to, or independent of, the beneficial effects on T2DM development is unknown. In 
DPPOS Phase 3 we will study the comparative effectiveness of the early initiation of metformin 
during pre-diabetes vs treatment only after the development of T2DM on cancer incidence. 
Potential mechanisms for metformin’s anticancer actions include a direct insulin-
independent anti-tumor effect via activation of the cellular energy signal AMPK55,56 and 
inhibition of mitochondrial oxidative phosphorylation57.  In addition, since insulin has mitogenic 
effects and tumor cells often express high levels of insulin receptor, metformin’s insulin 
lowering effects may also help reduce tumor development and growth. Benefits of metformin 
against breast, colorectal, pancreas, endometrial and prostate cancer have been suggested, but to 
date evaluations in clinical trials have focused largely on biomarkers and surrogate in vitro 
outcome58.  Definitive trials with randomized exposure and sufficient sample size, duration of 
exposure and follow up are needed to address the critical public health question of whether 
metformin reduces cancer risk.   
With continued differences in metformin exposure among the original treatment groups, 
and more cancer cases developing, DPPOS Phase 3 can examine the effect of randomized MET 
on cancer risk in an initially pre-diabetic population.  A pilot DPPOS project with NCI began in 

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2012 to lay the groundwork for this project, including providing an estimate of between group 
differences in cancer rates. 
As with the CVD outcomes, we are also interested in whether diabetes prevention via 
intensive lifestyle treatment is associated with reduction in cancer incidence, and whether any 
such effects are related to weight and weight loss with DPP interventions. DPPOS Phase 3 will 
also allow us to address these important potential public health impacts of DPP/DPPOS. 
 
3.3.3. DPPOS Phase 3: Diabetes Outcomes 
 
 
We plan to continue to ascertain diabetes development through ongoing testing of fasting 
glucose and 75g oral glucose tolerance testing. This outcome is no longer primary but the long-
term effects of the randomized therapies on diabetes and glycemia-related outcomes remain of 
interest, and this information will be needed for evaluation of the relationships of glycemia with 
other outcomes of interest.  
 
3.3.4. DPPOS Phase 3: Effects of Interventions on Microvascular Disease 
 
In DPPOS Phase 3 we will continue to ascertain microvascular disease components, 
including retinopathy and nephropathy as a prespecified combined outcome, and neuropathy 
alone and in combination with the others as secondary outcomes of interest. Some modifications 
to the measurements will be implemented, explained in detail below (Section 4.1.2). Effects of 
randomized treatments on progression to early and later microvascular disease will be evaluated, 
as well as the association with diabetes prevention, and in relationship to glycemia and glycemic 
exposure and to other outcomes of interest (for example blood pressure and weight changes). 
 
3.3.5. DPPOS Phase 3: Epidemiology of Microvascular Disease and Neuropathy in IGT 
and New-onset Type 2 Diabetes 
 
Epidemiologic59,60 and interventional studies, such as the DCCT61 and the UKPDS62 have 
contributed to our understanding of the relationship between glycemia and complications by 
performing secondary analyses that plot the development (or risk for progression) of retinopathy 
against mean HbA1c over time.  These studies have had to extrapolate to the non-diabetic range; 
there were too few patients with “normal” HbA1c results to provide reliable estimates of risk in 
the low diabetic or high normal levels of HbA1c.   
Better understanding of the clinical course of IGT and T2DM from the time of onset is 
critical for several reasons.  Establishing the precise relationship between glycemic levels and 
the occurrence of “diabetic” complications plays a significant role in determining the level(s) of 
glycemia at which diabetes is diagnosed and therapy is considered.  Moreover, such knowledge 
will contribute to our understanding of the pathogenesis of diabetic complications.  Among the 
major hypotheses to explain the pathophysiology of diabetic complications, the “glycation” 
hypothesis is probably the most in vogue and has the most mechanistic data associated with 
it63,64.  Since glycation occurs not only in red blood cells and hemoglobin, but also in all tissues 
and circulating proteins exposed to glucose, it should come as no surprise that there may be no 
specific threshold where one finds diabetic complications; rather, there may be a continuum of 
risk associated with glycemia, including in the sub-diabetic range. Through studies of pre-

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diabetic patients, i.e., IGT, and new onset diabetes, will we have the opportunity to explore the 
pathophysiology of diabetic complications.  
In the DPPOS Phase 3 we hypothesize that continued exposure to treatment-related 
differences in glycemia, owing to differences across the entire course of time since initiation of 
the DPP, will manifest as differences in microvascular disease prevalence.  
 
3.3.6. DPPOS Phase 3: Epidemiology of CVD in IGT and New-onset Type 2 Diabetes 
 
In addition to examining potential differential effects of the randomized interventions on 
CVD, atherosclerosis and CVD risk factors, further follow-up of the DPP cohort, with its IGT 
and newly diagnosed T2DM subjects, should shed light on the clinical course of CVD, 
atherosclerosis, and CVD risk factors in various states of glucose intolerance and during the 
transition from IGT to diabetes. This remains of interest with the transition to DPPOS Phase 3, 
which provides an opportunity for extended evaluations of these relationships into the period 
when clinically evident CVD will manifest.    
Numerous studies have demonstrated that subjects with diabetes have a 2-4 fold 
increased likelihood of developing CVD65. It is generally believed that this increased risk for 
atherosclerotic vascular disease is driven by multiple risk factors, including dyslipidemia, 
hypertension, a procoagulant state and hyperglycemia itself, which frequently cluster in these 
individuals, linked together by insulin resistance and decompensating beta cell function66-68.  The 
natural history of atherosclerotic vascular disease in IGT and diabetic subjects is not well 
understood. An increased risk for CVD in T2DM subjects is clearly present at the time of clinical 
diagnosis of diabetes69. Moreover, CVD risk factors associated with insulin resistance, such as 
higher blood pressure, and triglyceride levels, fibrinogen and PAI-1, and reduced HDL-
cholesterol levels, are found in normoglycemic adult subjects who go on to develop diabetes 8 
years later, compared with those who do not, suggesting that the substrate for the increased risk 
for atherosclerosis is present many years prior to the development of diabetes.  Atherogenic risk 
profiles accompany increasing glycemia in the sub diabetic range67,68.  However, little is known 
about the subclinical and clinical course of atherosclerosis during the period when glucose 
tolerance becomes impaired, followed by development of diabetes.   
Most reported studies suggest that the risk for CHD in IGT is intermediate between that 
in the general population and that in diabetic individuals66.  However, some studies have not 
detected any difference in CHD frequency between normal glucose tolerance (NGT) populations 
and those with IGT, and others have found differences in men or women only70,71.  Most of these 
studies were cross-sectional and many of the older surveys did not utilize the WHO diagnostic 
criteria to define IGT and are therefore difficult to interpret.  Among prospective studies in 
subjects categorized into NGT and IGT groups according to WHO criteria, a Finnish 
investigation found no difference in CHD incidence72. 
In addition to differences in the demographics, categorization of subjects, and study 
design influencing the apparent risk of CVD, the prognostic and metabolic heterogeneity of 
individuals with IGT inevitably must influence the intrinsic natural history of CVD in these 
subjects.  Although there is little disagreement that T2DM is associated with a higher risk of 
CVD than is IGT, the reason(s) for these differences are not known.  It is likely that those 
individuals with IGT who develop diabetes within a given period have a greater risk than those 
who do not; however, this has not been studied.  Furthermore, there is no information about the 
risk factor profile or CVD incidence in newly converted diabetic subjects relative to those with 

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IGT, or with longer duration diabetes.  Finally, the relationships between established and newer 
CVD risk factors to subclinical and clinical CVD measures in subjects with IGT and newly 
diagnosed T2DM diabetes, and whether they differ between these two entities has not been 
studied.  Of particular interest is whether glycemia per se is a determinant of increased CVD risk 
in subjects who convert from IGT to diabetes.  Thus, a long-term prospective follow-up study of 
CVD risk factors, and subclinical and clinical measurements of CVD in a population with IGT, 
some of whom develop diabetes within the study period and continue to be studied, will provide 
critical information on the evolution of cardiovascular disease and the factors that influence it, in 
the preclinical phase of diabetes. 
DPPOS Phases 1 & 2 provided the opportunity to examine CVD, atherosclerosis, and 
CVD risk factors in a large, demographically diverse, prospectively studied population with IGT 
and newly diagnosed diabetes. Repeated measures of glycemia and CVD risk factors during and 
after the DPP made possible a large number of analyses that have never been possible before. 
We have observed significant treatment-related differences in CVD risk factors42 (Figure 5) with 
major between-group differences seen in the 3-5 years after randomization. Also, we have 
analyzed a collection of CVD biomarkers and identified treatment-related differences in C-
reactive protein and tissue plasminogen activator43, as well as adiponectin73, which suggest 
graded beneficial effects on CVD risk. By extending this assessment for a further 5-10 years into 
DPPOS Phase 3, there should be a sizable group of diabetic subjects who will have been studied 
through a phase of IGT and into a phase of diabetes, each lasting several years.  Since the date of 
development of diabetic hyperglycemia is known within 6 to 12 months, it will be possible for 
the first time to track CVD risk factors, and subclinical and clinical outcomes as a function of 
this transition.   
 
 
Figure 5. Changes in major CVD risk factors in the DPP cohort 
 

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The DPPOS cannot strictly be viewed as a natural history study of IGT, nor of 
“undiagnosed diabetes” since both of these groups of subjects will have received more study- as 
well as non-study-based treatment in DPP and in the post-DPP period of follow-up than would 
occur naturally in the population.  However, it is entirely possible that the most important 
determinant of CVD incidence in our entire study population may be whether participants 
develop diabetes or not, regardless of the interventions they have received.  Such a finding would 
be of great importance to the conception of diabetes prevention.  In addition, the relationships 
found to exist in this study between CVD risk factors and CVD subclinical and clinical outcomes 
will be informative, independent of interventions. We will carefully assess concurrent 
medication use during the follow-up study, since several effective medications for hypertension, 
dyslipidemia, and renoprotection are now available and will increase in use over time.  Since 
there is evidence that blockade of the angiotensin system may slow progression to diabetes, use 
of these agents will also be assessed25,74.    
 
 
3.4. 
Other important DPP/DPPOS Analyses 
 
3.4.1. Economic Implications 
 
The economic impact of the DPP treatments will be a function of any significant 
differences in health outcomes over time.  Diabetic patients experience higher health care costs 
than do non-diabetic persons75.  During DPPOS, an “in trial” health economic analysis was 
performed, using the actual data regarding health care utilization (e.g., medications, 
hospitalizations) and the calculated costs of the interventions over time. The results76 
demonstrated that metformin therapy was cost-savings and both the life-style intervention and 
metformin were cost effective, with improved QALYs in ILS and MET compared with PLB.  
These analyses have not considered the potential long-term effects of the DPP on complications. 
In order to understand the true costs and benefits of DPP interventions, we must delineate the 
long-term clinical outcomes associated with the interventions.  Reduced long-term health care 
costs associated with the DPP interventions that delay diabetes and, presumably, diabetes-
associated complications, would offset the costs of the interventions and therefore favorably 
affect the cost-effectiveness and cost-utility ratios. 
In DPPOS Phase 3 we will be able to extend these analyses to the effects of prevention 
of diabetes-related complications, incorporating the costs of screening and long-term treatment in 
order to produce the anticipated prevention effect. These analyses will be considerably 
strengthened by quantifying the true prevention effect as it relates to micro- and macrovascular 
disease, as well as any effects on cancer and effects on age-related infirmity. 
 
3.5. 
Effects of Race-ethnicity and Sex 
 
Over 45% of the DPP participants belong to a US minority racial or ethnic group: at 
baseline, 19.9% were African American, 15.7% Hispanic American, 5.3% American Indian, and 
4.4% were Asian American.  A very similar distribution by race-ethnicity has continued during 
DPPOS. The majority of clinics enrolled >25% of participants from at least one non-Caucasian 
group.  The major DPP study results suggested that the active interventions were effective across 
all racial-ethnic groups in the study, based on a negative test for heterogeneity6.  However, the 
same questions posed for the entire DPP cohort in DPPOS are highly relevant in the individual 

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ethnic-racial groups. The long-term effects of DPP interventions on clinical outcomes and the 
clinical course of IGT and new-onset T2DM are especially important in the minority populations 
because of the increased prevalence of T2DM in these groups, compared with the general 
population77-81, and the suggestion, based on limited data, that the clinical expression of diabetes 
with regard to complications may be different between ethnic-racial groups.  The long-term 
follow-up may shed light on ethnic-specific contribution of vascular risk factors for the 
development of micro- and macrovascular complications associated with diabetes or IGT.  
Similarly, there are limited data regarding the impact of sex on the development of diabetes and 
its complications.  Finally, though epidemiological studies have characterized the prevalence of 
diabetes in minority racial/ethnic populations, such studies have generally not provided ethnic, 
age, or sex-specific incidence rates.  The highly compliant and motivated DPP cohort represents 
an excellent opportunity to examine these issues. 
 
3.5.1. Risk Factors for Type 2 Diabetes and Diabetes-related Complications in Minority 
Populations 
 
Risk factors for diabetes and its vascular complications such as IGT, decreased insulin 
sensitivity, hyperinsulinemia, central obesity, overweight, hypertension and gestational diabetes 
are more prevalent in African Americans82. Diabetic retinopathy also appears to be more 
common in African Americans with T2DM83. In the cross-sectional Baltimore Eye Study, there 
were equal rates of blindness secondary to diabetic retinopathy in Blacks and Whites84.  Other 
studies have reported the prevalence of blindness to be twice in Black compared with White 
individuals and of severe visual impairment to be 40% higher among African Americans85.   The 
prevalence of retinopathy in Blacks with T2DM in the 1988-1991 phase of NHANES III was 
higher than the rate in non-Hispanic Whites (NHW) but similar to that in Mexican Americans, 
though these data may reflect the higher rates of hypertension and poor diabetes control85. 
Similar confounders complicate the interpretation of the 2.6 to 5.6 fold higher rates of 
end-stage renal disease (ESRD) in Black compared with White Americans with diabetes86. 
Complications of diabetes including retinopathy, nephropathy, ESRD, lower extremity 
amputation (LEA), heart disease and stroke are all more prevalent among American Indians than 
among Whites79.  Complications of diabetes among Hispanics have largely been studied in 
Mexican Americans. The San Antonio Heart Study and NHANES III reported a greater 
prevalence of microvascular complications with 4.5 to 6.6 fold higher rates of ESRD than the 
general diabetic population and diabetic retinopathy being ~2 times more frequent in Mexican 
Americans, though this has not been confirmed in all studies86-88.  These data regarding ESRD 
cannot be easily extrapolated to milder degrees of nephropathy.  
Diabetic neuropathy is inherently difficult to study since measurement of nerve 
dysfunction has not been commonly performed in large epidemiological cohorts.  While lower 
extremity amputations may be a robust marker for severe peripheral sensory neuropathy, it 
represents a late stage of disease, frequently coincident with peripheral vascular disease and is 
relatively infrequent. 
Cardiovascular disease is the major factor underlying the high mortality rates observed in 
T2DM.  It is generally accepted that CVD rates in African Americans with diabetes are lower 
than the rates in NHWs89. Lower rates of heart disease have been reported in Mexican American 
men, compared with NHW men, but not in Mexican American women compared with NHW 
women90. 

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In none of these cross-sectional reports are minorities and NHW as well matched for 
demographic characteristics, risk factors, and comorbidities as in the DPP.  The longitudinal 
follow-up and careful characterization of the DPP cohort should help to delineate the risks of 
developing diabetes and its long-term complications in men and women and in the ethnic-varied 
groups represented in the study. 
In the DPPOS Phase 3 we will continue to perform pre-specified analyses comparing the 
sex and race/ethnicity subgroups, as these outcomes carry important implications for the entire 
population and benefits may differ among these groups. 
 

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4. 
DEFINITION OF OUTCOMES 
The outcomes for DPPOS Phase 3 are similar to those from DPPOS Phases 1 & 2, 
except as noted specifically below. 
 
4.1. 
Primary Outcomes during DPP and DPPOS  
 
4.1.1. Diabetes and Glycemia: OGTT and FPG  
 
The primary outcome for DPP, DPPOS Phase 1 and a secondary outcome for DPPOS 
Phase 2 and Phase 3 is progression of oral glucose tolerance test (OGTT) results to confirmed 
diabetes, by ADA criteria14.  To assess progression to this outcome, an OGTT will be performed 
routinely on an annual basis through DPPOS visit year 12 and biennially thereafter under 
conditions described in the Manual of Operations. All biochemical laboratory outcomes will be 
measured at the DPPOS Central Biochemistry Laboratory.  If the OGTT result meets ADA 
criteria for diabetes of fasting plasma glucose ≥ 126 mg/dl or 2 hour plasma glucose ≥ 200 
mg/dl, the participant will be called back for a repeat OGTT within 6 weeks.  In order to 
minimize the unmasking of participants and investigators to a positive but unconfirmed OGTT 
result, a subset of participants who do not have OGTT results positive for diabetes will be chosen 
by the Coordinating Center for repeat OGTT.  If two sequential OGTTs, performed within a goal 
of 6 weeks of each other, are positive for diabetes, the clinic and the participant will be notified 
of the results and the participant will be considered as having reached the diabetes outcome.  If 
the second test does not meet ADA criteria for diabetes (unconfirmed status), no such 
notification will be made and the participant will continue on the assigned treatment. In addition, 
as a safety measure, participants will be monitored with a fasting plasma glucose (FPG) semi-
annually through DPPOS year 12 and annually beginning in year 13 or at any time symptoms 
suggestive of decompensated diabetes are noted.  If this FPG is ≥126 mg/dL [7.0 mmol/L], the 
participant will be called back for a repeat FPG within 6 weeks.  If the repeat is also ≥ 126 
mg/dL [7.0 mmol/L], the participant will be considered as having reached the primary outcome, 
the participant and treatment team will be informed (see section 7.5.6).  Again, to maintain 
masking, the Coordinating Center will ask for a random repeat FPG on a subset of non-diabetic 
participants with FPG < 126 mg/dL [7.0 mmol/L]. In years without a scheduled OGTT, if 
HbA1c ≥6.5% and fasting glucose is <126 mg/dl, a confirmatory OGTT will be performed.  If 
the OGTT meets the diagnostic criteria for diabetes, the participant will be notified of the results 
and the participant will be considered as having diabetes. Otherwise, the participant will have not 
met the criteria for diabetes. 
Finally, any participants who develop symptoms consistent with hyperglycemia will be 
encouraged to contact the clinic as soon as possible so that an FPG can be measured.  If the FPG 
is ≥126 [7.0 mmol/L], the testing strategy outlined above will be followed. 
Criteria for the diabetes outcome: 
1 FPG ≥126 mg/dL confirmed within a goal of 42 day interval 
2 2 hour OGTT sample ≥200 mg/dL confirmed within a goal of 42 day interval 
3 FPG ≥ 126 mg/dL or 2 hour OGTT sample ≥ 200 mg/dL confirmed on two separate visits 
within a goal of 42 day interval. 
4 HbA1c ≥ 6.5 mg/dL and FPG<126 mg/dl when OGTT sample not collected and 
confirmation by FPG or 2 hour OGTT within a goal of 42 day interval. 

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The scheduled OGTT will be postponed for up to six weeks if a temporary concomitant 
condition exists that would affect glucose tolerance. When a participant has been in a "time-out" 
(other than for pregnancy), such as for a concomitant disease known to affect glucose tolerance, 
the fasting glucose assessment or OGTT will not be assessed at the scheduled visit.  Cases of 
diabetes diagnosed outside the study will be adjudicated by the study’s Outcomes Committee. 
For DPPOS Phase 2 and Phase 3, the further development of diabetes, and the effects of 
the original interventions on the development of diabetes over the entire course of the 
DPP/DPPOS, remain important secondary outcomes.  
 
4.1.2. Composite Diabetes-related Microangiopathic and Neuropathic Outcome 
 
The diabetes-related microangiopathic primary outcome for DPPOS Phase 2 was defined 
as a composite of the following at the year 11 visit, or if the participant is deceased or lost to 
follow-up before year 11, as of his/her last assessment: 
 
a. Nephropathy: increased albuminuria (≥30 mg/gram creatinine, confirmed), or renal 
dysfunction (end-stage renal disease, dialysis or renal transplant) or eGFR < 45  ml 
per min based on serum creatinine,  using the CKD-EPI equation; the qualifying 
criteria confirmed) 
b. Retinopathy: retinopathy by fundus photography (ETDRS grade of 20 or greater) or 
adjudicated history of laser or other treatment for retinopathy or 
c. Neuropathy: reduction or absence of light touch sensation to monofilament (Semmes-
Weinstein 10 gram) in either foot (< 8 of 10 applications detected). 
 
If a participant took antihypertensive drugs at the last assessment and did not meet 
the ACR or eGFR criteria at that time, he or she was considered to have reached the 
nephropathy outcome if the nephropathy criteria were met at 2 consecutive past visits. 
This substituted for the occurrence of nephropathy at year 11. 
 
For DPPOS Phase 3, the main composite diabetes-related microangiopathic outcome, 
now a secondary outcome, is defined as time to first occurrence of nephropathy or retinopathy, 
the two microvascular disease components that are most objectively measured microvascular 
complications. Nephropathy is adapted from KDIGO91 for categories of moderately increased 
albuminuria or moderately to severely decreased eGFR and defined as development of any of the 
following: (1) confirmed elevated albuminuria (≥30 mg/g creatinine) based on annual spot urine; 
(2) confirmed eGFR by CKD-epi15 <45 ml/min; (3) kidney transplant; or (4) dialysis for end-
stage renal disease. The definition of the retinopathy outcome will change from microaneurysms 
(ETDRS≥20) as used in DPPOS Phase 2 to mild diabetic retinopathy (ETDRS≥35)16 or 
adjudicated treatment for retinopathy. Macular edema by optical coherence tomography 
(OCT)92,93 will be a secondary outcome. The ETDRS grade was modified in recognition of the 
expected increase in time and level of hyperglycemia that will result in more diabetes-specific 
lesions and to minimize noise from aging related retinal findings. Spectral domain OCT is a 
noninvasive imaging technology that uses principles of light interferometry and Fourier analysis 
to generate a voxel (3-dimensional) rendering of the retinal architecture. OCT has become 
widely used in medical ophthalmology practice and in clinical research and is the standard of 
care imaging modality for diagnosis and management of diabetic macular edema. Analyses will 
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(DSPN) will be measured with the symptom questionnaire from the Michigan Neuropathy 
Screening Instrument used in previous years and, beginning in 2018, signs of neuropathy will be 
detected using quantitative measurements of vibration, light touch and sharp (pin prick) 
sensation, as recommended in the 2017 ADA Position statement94. The MNSI questionnaire and 
the monofilament test will be continued, as in past examinations, to allow longitudinal analyses. 
The principal outcome for DSPN in DPPOS Phase 3 will be defined as the presence of DSPN 
symptoms (score ≥4 on the MNSI questionnaire)95 or any signs of bilateral DSPN. The signs of 
bilateral DSPN require abnormal finding on both toes for pinprick testing (score ≥5)96, for 
vibration testing (score≥5)96, or for light touch sensing (<8 detected from 10 monofilament 
applications on each toe). Secondary analyses will include the presence separately of DSPN by 
symptoms or by signs, the presence of symptomatic DSPN confirmed by signs, and the 
individual elements of the neurologic sensory examination.  
 
4.1.3. Cardiovascular Disease  
  
The primary outcome of the second 5-years of DPPOS Phase 3 is the incidence of major 
cardiovascular disease (MACE).  MACE is defined as the time to first occurrence after DPP 
randomization of one or more of the following: fatal and non-fatal myocardial infarction and 
stroke or other cardiovascular death.   
 The composite diabetes-related cardiovascular disease secondary outcome is defined as 
the time to first occurrence of one or more of the following: a) cardiovascular disease (CVD) 
events (CVD death, fatal and non-fatal myocardial infarction and stroke), b) silent myocardial 
infarction on EKG97, c) coronary artery stenosis ≥ 50% documented by angiography, d) coronary 
revascularization, e) hospitalized CHF, f) hospitalized unstable angina/acute coronary syndrome, 
or g) revascularization or amputation in lower extremity not caused by major trauma. Secondary 
outcomes will also consider each of these components separately as well as arrhythmias.  
All CVD events are determined at the time of their report using a standardized medical 
history questionnaire and adjudicated after medical records are available by an outcomes 
committee whose members are blinded to treatment group. 
 
4.1.4. Cancer  
 
The primary outcome of the first 5-years of DPPOS Phase 3 is the incidence of new 
primary cancer (excluding non-melanoma skin cancer) with pre-defined obesity-related cancers 
and cancer mortality as secondary outcomes.  Obesity-related cancers will be defined prior to 
analysis of this outcome by investigators masked to the cancer outcome results.  Due to sex-
specific differences in cancer types, stratified analyses by sex are also planned.  A recurrence or 
metastasis of a cancer previously diagnosed prior to DPP randomization does not count towards 
this outcome.  Relevant medical records for all DPP participants with a history of cancer 
diagnoses or reported cancer deaths are included, even from participants who did not enroll in 
DPPOS.  Medical records are obtained and include pathology reports, notes from biopsy 
procedures or surgeries, hospital discharge summaries, radiology reports cancer staging forms, 
and ER/PR/Her2 (breast cancer only). Records are de-identified and redacted to obscure 
metformin exposure. Cancer events are adjudicated by a trained National Cancer Institute 
physician. 
 

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4.1.5. Determining Vital Status and Cause of Death for Participants 
 
The National Death Index (NDI) or an external people-search service will be used to 
search for DPP and DPPOS participants who have not been seen at their local center and have 
not been able to be contacted for more than 1 year, as well for deceased participants. The NDI is 
a central computerized index of death record information from State vital statistics offices 
nationwide. Each center will submit their cases to the NDI or people-search service. Coding that 
includes cause of death will be obtained. Records will be searched for all years for which vital 
status cannot be confirmed.  If permitted by the local IRB, follow-back investigations will be 
undertaken to obtain medical records and next-of-kin interviews as required. Central review of 
cause-of-death will be adjudicated by an outcomes committee whose members are blinded to 
treatment assignment. 
 
4.1.6. Medicare database 
 
The DPPOS may undertake a search of the Centers for Medicare and Medicaid Services 
(CMS) database for the purpose of determining diagnosis codes and dates for health care 
utilization to supplement medical records. 
 
4.2. 
 Other Secondary Outcomes 
 
The DPPOS secondary outcomes were selected for their importance to the clinical and 
scientific interpretation of the study.  They might help explain the mechanism of the primary 
outcome results, or shed light on how the interventions affect secondary outcomes and their risk 
factors.  Secondary outcomes may be assessed in the study population as a whole or in subsets, 
depending on feasibility, cost and the likelihood of deriving significant results from a subset.  All 
biochemical laboratory outcomes will be measured at the DPPOS Central Biochemistry 
Laboratory.  Clinical center staff and study participants are notified if a secondary outcome result 
falls outside a clinically acceptable range for that participant, constituting a concomitant 
condition.  The timing of outcome assessments is described in Chapter 12. 
Following is a brief summary of secondary outcomes that will be measured at specified 
intervals (see Chapter 12 for schedule) in all participants. Outcomes measured in DPPOS Phase 
1 and/or Phase 2 but not in DPPOS Phase 3 are noted in brackets: 
 
4.2.1. Glycemia and insulin secretion: 
 
• HbA1c: Hemoglobin A1c will be assessed to reflect recent average glycemia, to test 
its relationship to OGTT results and its utility as an indicator of glucose intolerance 
for the purposes of diabetes prevention, and as a predictor of microvascular and 
macrovascular outcomes. 
• Insulin and glucose measurements during the OGTT. 
 
4.2.2. Cardiovascular disease and risks, assessed by: 
 
• Electrocardiogram 
• Cardiovascular symptom and disease assessment 

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• History of serious cardiovascular disease events 
• Arm blood pressure 
• [Ankle/arm systolic blood pressure: Ankle-brachial index] 
• [Coronary artery calcium]  
• [Fibrinolysis and clotting factors: Fibrinogen, tissue plasminogen activator and C-
reactive protein] 
• Lipoproteins:  Lipid profile (total cholesterol, total triglyceride, HDL-cholesterol and 
derived LDL-cholesterol), or beta quantification in the setting of hypertriglyceridemia  
(specifically measuring LDL-cholesterol), [LDL particle size and sub fractions] 
• Cardiovascular risk profile 
 
4.2.3. Retinopathy, assessed by: 
 
• Fundus photography  
• History of documented laser surgery for diabetic retinopathy 
• Macular edema by OCT 
  
4.2.4. Nephropathy, assessed by: 
 
• Albumin excretion: Urinary albumin and creatinine concentrations for albumin 
excretion, using a spot collection. 
• Serum cystatin  
• Serum creatinine 
• History of end-stage kidney disease treated with dialysis or transplantation 
 
4.2.5. Neuropathy, assessed by:  
 
• Semmes Weinstein 10 gram monofilament examination 
• Examination of vibration sensation 
• Examination of pinprick sensation 
• Michigan Neuropathy Screening Instrument Questionnaire 
• EKG rhythm strip:  to measure heart rate variability 
 
4.2.6. Physical activity, nutrition, behavioral measurements, and body weight and obesity, 
assessed by: 
 
• Physical measurements: Height, weight, waist circumference, BMI   
• DXA: Measures of bone density, whole body composition and vertebral fractures in a 
sample of participants 
• Physical activity: Standardized questionnaire assessment  
• [Nutrient intake: A semi-quantitative food frequency questionnaire.] 
• [Behavioral:  Dietary restraint, Exercise Self-Efficacy, Low Fat Diet Self-Efficacy] 
 
4.2.7. Health related quality of life, assessed by: 
 

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• Psychosocial: Beck [Anxiety and] Depression Inventories and the MOS SF-36, to 
assess mood and general adjustment and health related quality of life 
• Cognitive performance  
• Physical functioning 
• Healthy Aging Index98  
• Urinary incontinence 
• Activities of Daily Living and Instrumental Activities of Daily Living  
• Sexual function (by standardized questionnaires) 
• Pulmonary function by spirometry   
• Cardiorespiratory fitness measured by the 6-minute walk test 
• Fractures (hospitalized spine, hip or appendicular fracture, adjudicated) 
• Infections (hospitalized, self report) 
 
4.2.8. Resource Utilization, Costs, Health Utilities, and Effectiveness of treatments 
The study will continue to collect information on resource utilization and costs associated 
with the interventions and with medical care received outside of the study, as well as 
information on health-related quality-of-life and survival.  From these data, medical costs 
of the interventions and medical care outside of the study will be computed, and 
compared among the treatment groups.  Differences in quality-adjusted life-years gained 
will be compared by treatment group.  The information used in the health economics 
analyses will be obtained with: 
• Quality of Well-Being Scale: A preference-based measure for overall health used for 
quality-adjusted life year’s computations. 
• Resource utilization instruments: Questionnaires to capture resource utilization from 
the perspectives of the participant, and of the DPPOS staff. 
• Hospitalizations 
 
4.2.9. Safety tests: 
• Routine chemistry testing: Serum creatinine  
• Serious adverse medical events and symptoms: Queries for serious adverse events.  
Medical records will be gathered in the case of significant cardiovascular intercurrent 
medical events, reports of cancer diagnosis, and hospitalizations for infection or for 
spine, hip or appendicular fractures.   
• Pregnancy testing: As needed for metformin-treated participants, based on symptoms 
and menstrual history. 
• [CBC: for metformin-treated participants, measured locally] 
• Vitamin B12: for metformin-treated participants 
 
4.2.10. Serologic evidence of type 1 diabetes, assessed by: 
• [Samples for IA2 and GAD antibodies at time of diabetes conversion] 
 
4.2.11. Stored specimens: 
• Sample storage: Samples of plasma, serum and urine will be stored for possible future 
analyses related to IGT and Type 2 Diabetes, and their complications.  Samples for 
DNA were collected during the DPP. 

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4.2.12. Other chemistries: 
• [Relevant biological markers related to the pathogenesis of diabetes and its 
complications] 

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5. 
STUDY DESIGN 
 
5.1. 
 Overall Design 
 
The DPPOS is a prospective study of the effects of DPP interventions on continued 
prevention or delay of diabetes, and on preventing or ameliorating its complications, specifically 
diabetic microangiopathy, neuropathy, cancer and cardiovascular disease.  The rationale for the 
overall design is to provide maintenance of therapies found to be effective in DPP to assess the 
long-term impacts on diabetes prevention and complications. 
All DPP participants were offered the opportunity to participate in the group lifestyle 
intervention protocol during the Bridge period, January through June 2002.  They were offered 
the opportunity to continue a long-term maintenance of the lifestyle intervention program, 
consisting of quarterly Healthy Lifestyle Program (HELP) meetings through spring 2014.  In 
addition, DPP intensive lifestyle participants were offered 4 weekly or bi-weekly behavior boost 
sessions in groups twice yearly through 2014, and DPP metformin participants were provided 
open label metformin (850 mg bid).  During DPPOS Phase 3, participants will remain in their 
originally randomized treatment groups, except that those in the original troglitazone group are 
no longer being followed.  All participants will be offered a single Group Lifestyle (HELP) 
session annually.  Participants in the original metformin group will continue to receive study 
metformin per protocol.  Participants in the original ILS group will receive an additional 
“lifestyle check-up” during their annual visit.  These interventions are summarized below: 
 
DPP 
DPPOS Phases 1 & 2 
DPPOS Phase 3* 
Intensive lifestyle (ILS) 
Blinded Metformin + standard LS (MET) 
Blinded Placebo + standard LS (PLB) 
Troglitazone + standard LS (stopped in 1998) 
(TRO) 
Boost LS + HELP 
Open label metformin + HELP 
Group lifestyle (HELP only) 
Group lifestyle (until 2008) 
HELP plus annual lifestyle check-up 
HELP plus open label metformin 
HELP 
N/A 
*Single group lifestyle session offered annually to all participants 
 
During DPPOS Phases 1 & 2, participants had twice-yearly scheduled visits.  During 
DPPOS Phase 3, participants will have an annual in-person visit. The mid-year assessment will 
be conducted by telephone, unless an in-person visit is required or is requested by the participant. 
Study outcomes, including health outcomes assessments , a brief medical history, fasting and 
OGTT blood draws, questionnaires, anthropometric measures, fundus, and neurologic 
examinations, and measures of subclinical atherosclerosis are performed as stipulated in Section 
12. 
Assessment of microangiopathic, cancer, and cardiovascular outcomes will be performed 
in both diabetic and non-diabetic DPP participants during all years of the DPPOS.  Both 
individual and composite outcomes will be assessed.  The long-term effects and cost-
effectiveness of interventions on the incidence and determinants of these outcomes will be 
assessed based on the original randomly assigned interventions during DPP.   
In addition to the primary and secondary objectives, separate analyses will be performed 
to assess the importance of development of diabetes and other determinants on the development 
of microangiopathic, cancer and cardiovascular outcomes. Subgroup analysis will be performed 
based on sex, age and race/ethnicity. 
 

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5.2. 
 Participation Criteria 
 
All DPP participants are eligible to participate in the DPPOS, except for those originally 
randomized to troglitazone.  Inability to attend group sessions for logistical or heath reasons will 
not be a criterion for exclusion.   
 
5.3. 
 Procedures for obtaining surrogate consent  
 
The following surrogate consent issues will require approval by local IRBs. Some IRBs 
may require different procedures for following participants who do not have the capacity to 
consent. Each clinical center will follow procedures approved by its IRB. Participants who have 
the capacity to consent will be given the opportunity to decide in advance whether they do or do 
not want a surrogate to make decisions for them to continue their participation in the study 
should they lose capacity to consent in the future. This will be documented on the procedures 
consent note in their research chart. For those participants who choose not to have a surrogate 
make enrollment decisions for them in the future and lose the capacity to consent, this will be 
documented and the participant will be excluded from further participation after losing the 
capacity to consent. 
• Staff persons will discuss with the participant who they have chosen as a surrogate or 
who they would like to serve as a surrogate decision maker. 
• Staff persons will ascertain that the following can serve as a surrogate:  first-degree 
family members (sibling, spouse, or an adult son or daughter), health care proxy, legally 
appointed guardian, or participant-chosen surrogate, in accordance with local, state and 
IRB regulations. 
• Participants will be encouraged to discuss their future research participation with the 
surrogate. 
 
 
Participants may also provide consent to have a surrogate provide health information 
including the assessment of cognitive ability. 
 
5.4. 
 Principles Guiding the Selection of a Study-wide Group Lifestyle Intervention 
 
The decision to offer effective therapy to the DPP cohort at study end was based on the 
sense of the DPP Research Group and NIDDK that initiating effective therapy was consistent 
with our obligation to the participants who had made the DPP possible.  Although this decision 
was not based on any scientific imperative, the Research Group did not think that it would 
interfere with the follow-up study as designed.  Continuing to apply the DPP interventions 
during DPPOS was based on the expectation that a positive effect of DPP interventions on long-
term health outcomes would more likely be obtained if the interventions that were effective in 
DPP were maintained to some degree in the DPPOS, recognizing that the DPP placebo group 
would now receive lifestyle intervention as well.  This design for DPPOS was thought more 
likely to minimize confounding of the effects of the past DPP interventions through the 
introduction of non-standardized therapies by participants and their health care providers. 
During the final six months of the DPP (January – June 2002) all participants in the 
original MET, PLB, and TRO groups were offered the Healthy Lifestyle Program (HELP), an 

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intensive program with the same goals used in the DPP, but provided in a group, rather than an 
individual setting (DPP Bridge Protocol, version 4.5). During this period, the former ILS group 
continued with the DPP ILS program, albeit with less frequent contact than during the DPP, 
owing to resource limitations, and attended the HELP sessions if they desired.  In DPPOS Phases 
1 & 2 all participants were offered quarterly group sessions to encourage the maintenance of 
their lifestyle interventions until June 2014.  These meetings helped to encourage continued 
participation in the DPPOS.  The use of twice yearly behavior boost groups for the DPP ILS 
participants was intended during DPPOS years 1-12 to reinvigorate their previous efforts at 
achieving weight reduction and increased physical activity in a manner that requires only modest 
staff involvement.  Beginning in year 13 and continuing in DPPOS Phase 3, lifestyle messages 
will be reinforced during regularly-scheduled outcomes visits and at one annual HELP lifestyle 
class offered to all participants. During DPPOS Phases 1 & 2, and Phase 3, metformin was and 
will be provided to all participants who were receiving metformin treatment in DPP, assuming 
that HbA1c is <7.0% and the participant has not developed a contraindication or intolerance to 
metformin, in order to maintain long-term intervention with this agent.  (See section 7.2.2 
regarding HbA1c ≥ 7.0%.)  The provision of lifestyle training to the DPP PLB group during 
years 1-12 may reduce differences in long-term outcomes between intervention groups.  The 
potential benefits of the active interventions during DPP on long-term outcomes, combined with 
efforts to boost the earlier impact of intensive lifestyle management, and continuing with 
metformin treatment, provide the opportunity to examine and compare the long-term effects of 
these interventions on an intention-to-treat basis. 
 
5.5. 
Masking 
 
There will be no masking of participants to OGTT or lipid results, other than in the case 
where confirmation of a positive test for diabetes is pending (or during a random repeat fasting 
glucose or OGTT). Metformin is dispensed as open label. 

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6. 
PARTICIPANT MANAGEMENT PROTOCOLS 
 
Each participant continues follow-up according to his or her original DPP randomized 
assignment.  Metformin will continue to be provided to the original Metformin participants 
throughout DPPOS. The HELP program will be held once annually and Boost programs were 
discontinued beginning with DPPOS year 13. 
 
6.1. 
 Schedule of Follow-up Visits 
 
During DPPOS Phases 1 & 2, follow-up visits for outcome assessments were scheduled 
at 6-month intervals. Annual visits were targeted for the anniversary of the participant’s original 
DPP randomization date.  HELP group meetings were offered four times per year, at several 
different times at each clinic in order to make convenient meeting times available for a large 
number of participants for years 1-12 and annually thereafter.  Boost sessions were offered twice 
per year, and similarly scheduled multiple times for purposes of convenience for years 1-12. 
Except for participants from the original Troglitazone group, who ceased study participation 
beginning with protocol version 3.0, all participants will continue their scheduled follow-up 
visits for the duration of DPPOS regardless of their level of compliance with the assigned 
treatment.  Outcome and safety assessments will be conducted according to the schedule in 
section 12. 
Beginning in study year 13 and continuing in DPPOS Phase 3, in-person annual visits 
will continue with reduced intensity of outcome measurements according to the outcomes 
schedule (See section 12). Mid-year visits will be brief, and held primarily by phone or in person 
as needed. The original DPP ILS participants may participate in a brief annual lifestyle check-up 
to reinforce lifestyle goals.  Participants originally assigned to metformin who have not 
developed diabetes, or who have developed diabetes but have continuously maintained HbA1c 
<7% at (based on results from their annual visit) will continue to be provided study metformin. 
(See section 7.7.2 regarding HbA1c ≥ 7.0%.)   
 
6.1.1. Interim Visits 
 
An interim visit refers to all visits other than scheduled follow-up visits.  Interim visits 
may be required for the monitoring or management of an emerging or existing medical 
condition, or to repeat procedures that were found to be deficient at a previous visit.  Such visits 
may be held as frequently as deemed necessary. 
 
6.1.2. Confirmation (CON) Visits 
 
In order to confirm selected outcomes, confirmation (CON) visits are required whenever 
a participant has an elevated fasting (≥126 mg/dl), stimulated (≥200 mg/dl) glucose, or for 
annual visits without a scheduled OGTT collection, an HbA1c ≥6.5%.  If urine albumin level 
≥30 mg/gm creatinine or eGFR < 45 is first demonstrated in DPPOS year 11 and 16 visits, 
participants will be asked to return so that a repeat urine or blood sample can be obtained for 
confirmation. 
 
 
6.1.3. Suspension of Follow-up Visits 

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The occurrence or presence of the following will constitute suspension of the scheduled 
follow-up protocol:  Voluntary withdrawal by the participant, or a condition that, in the opinion 
of the principal investigator, makes it unsafe for the participant to continue.  Efforts to return 
participants to an active status will be made regularly, as appropriate. 
 
6.1.4. Home or Telephone Visits  
 
A home visit is any visit outside the DPPOS clinical center. Home visits will be used as 
needed and should not be used regularly to take the place of a clinic visit unless the participant is 
permanently unable to attend the clinical center. Local IRB issues should be addressed 
concerning off-site blood draws. All guidelines regarding the collection of outcome measures 
(such as fasting glucose) must be followed.  A study staff person who is certified to perform the 
listed outcomes will perform the home visit. The purpose of a home visit is to retain and /or 
reactivate participants and to collect important outcome data on participants who are having 
difficulty attending a clinic visit. Information on Serious Adverse Events will be collected at a 
home visit.  In rare cases, the home visit may also be utilized to perform a safety blood draw 
when a medication participant is unable to attend a clinic visit.  Home visits should only be 
conducted for participants who live relatively near the clinical center.  Clinic staff are not 
expected to travel great distances to visit any inactive participant. Clinics will decide whether or 
not a specific home visit is feasible, taking into account time, cost and risk.   
For those individuals who cannot travel and for whom a home visit is not possible, a 
telephone visit may be conducted to collect updated health history, Serious Adverse Events, 
CVD and cancer event information. 
 
6.1.5. Remote Visits  
 
For participants who have moved far away from any DPPOS clinic or have physical 
limitations that make them unable to come to a DPPOS clinic, a remote visit might be performed 
by a non-DPPOS staff person trained and certified in DPPOS procedures. The purpose of a 
remote visit is to retain participants and to collect important outcome data. Clinical center staff 
will arrange for the visits, and provide clear instructions to participants about what to expect. 
Weight and blood pressure will be measured, and routine annual visit blood and urine samples 
and safety specimens will be obtained at remote visits. Samples will be sent to the DPPOS 
laboratory identified by only the participant study number and data will be returned to the 
clinical center.  
 
6.1.6. Retention Monitoring and Recovery of Inactive Participants 
 
Retention of participants throughout the study period is key to both the power and 
generalizability of DPPOS findings.  Retention of DPPOS participants will be encouraged 
through the provision of social support from DPPOS staff during clinic visits, group meetings, 
and other incentives.  All participants receive an honorarium, at scheduled visits, in recognition 
of the time and effort spent in the DPPOS. 

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Monitoring activities that track participants’ attendance at scheduled clinic visits guide 
efforts to maximize retention.  Missing semi-annual and annual data collection visits triggers a 
graded hierarchy of recovery efforts designed to maintain participants’ involvement in DPPOS. 
 
6.2. 
Lifestyle Program in DPPOS Phases 1 & 2  
 
Recognizing that long term adherence to healthy eating and exercise behaviors and 
maintenance of moderate weight loss and physical activity require ongoing support and 
intervention, lifestyle intervention efforts were continued during the DPPOS for all previously 
randomized participants until the end of Phase 1, and for all but the former Troglitazone 
participants, who did not participate in DPPOS research beginning with protocol version 3.0. To 
maximize the chances of all participants achieving and/or maintaining the 7% weight loss goal 
and 150 minute weekly physical activity goal which was the cornerstone of the lifestyle 
intervention during DPP and the DPP Bridge, Healthy Lifestyle Program (HELP) maintenance 
sessions were provided quarterly to all DPPOS participants through spring 2014. In addition, 
participants who were previously randomized to the intensive lifestyle arm in DPP were given 
Boost Lifestyle Sessions in a group format, two times each year through spring 2014.  The goals 
of lifestyle treatment for all DPPOS participants was the same as for the lifestyle group during 
DPP: 
• Achieve a weight reduction of at least 7% of initial (at DPP baseline) weight and 
maintain this weight reduction  
• Achieve at least 150 min/week of moderate intensity exercise (such as walking 
and bicycling), and maintain this level of physical activity  
 
6.2.1. Lifestyle Resource Core and Lifestyle Advisory Group 
 
During DPPOS Phases 1 & 2, the Lifestyle Resource Core (LRC) and the Lifestyle 
Advisory Group (LAG) comprised of co-investigators and staff representing several DPPOS 
centers developed the materials for the HELP maintenance and Boost sessions and provide on-
going training and support for the lifestyle interventionists. All materials were reviewed and 
approved by the DPPOS Executive Committee prior to implementation. 
 
6.2.2. Staff for Lifestyle Interventions 
 
During DPPOS Phases 1 & 2, case managers, group lifestyle interventionists, and/or 
consultants at each clinical center carried out both arms of the lifestyle intervention.  
Interventionists were individuals with experience and/or training in nutrition, exercise, behavior 
modification, or group treatment.  Other staff (e.g. peer counselors and exercise leaders) were 
employed as appropriate at each center. 
 
6.2.3. HELP Program 
 
Following the delivery of the 16 session Healthy Lifestyle Program (HELP) that was 
offered to all previously randomized participants during the DPP Bridge, quarterly HELP 
maintenance sessions were offered to all participants during DPPOS Phases 1 & 2 (until the 
summer of 2014) . The purpose of the quarterly lifestyle sessions was to reinforce the basic 
content, as well as the weight loss and physical activity goals.  In addition, the quarterly sessions 

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served a participant retention purpose.  Small incentives, such as gift certificates and lifestyle-
relevant materials such as recipe books (gifts are valued in the range of $2-$10) were sometimes 
used to reward attendance and participation at these group education sessions.  Every effort was 
made to make the sessions topical, interesting, and fun (e.g. may involve doing cooking 
demonstrations, muscle resistance training, stress management and relaxation training etc.)  The 
quarterly sessions rotated annually through the following content areas: 
• Nutrition 
• Physical activity 
• Stress management/motivation/behavioral self-management 
• Diabetes prevention research updates 
• Diabetes research and management updates 
Each of the four sessions was offered up to 5 times in the quarter at each clinical center 
with approximately 20-40 DPPOS participants attending any one-class session.  Topics and 
lesson materials, handouts, and homework assignments were developed by the Lifestyle 
Resource Core and outlined in detail in the Lifestyle Intervention Manual of Operations for 
DPPOS.  The first quarterly session began within 2-3 months after DPPOS began.   
Annual HELP sessions will continue to be offered to all participants, regardless of 
randomized treatment group, during DPPOS Phase 3. 
 
6.2.4. Boost Lifestyle  
 
During the DPP Bridge period, DPP intensive lifestyle participants either attended the 
HELP group sessions and/or were encouraged to be seen individually by their lifestyle case 
managers at least every 8 weeks. During DPPOS Phases 1 & 2, these participants were offered 
Boost Lifestyle sessions in addition to Group Lifestyle sessions.  The purpose of Boost was to 
offer periodic, structured “restarts” for lifestyle arm participants who had already received 
intensive, long-term, individual lifestyle intervention.  The Boost sessions were intended to 
reinforce specific behavioral self-management activities (e.g., self-monitoring of fat, calories, 
and/or physical activity minutes as well as weight checks), which are important for weight loss 
and physical activity adherence and/or maintenance.  An additional focus of the Boost was to 
promote home-based behavioral self-management of weight and physical activity through the 
use of motivational campaigns.  In addition to reinforcing attendance at group sessions, 
incentives (valued at $5 - $20) were also be used to reward lifestyle behavior change such as 
designated weight loss goals, activity goals, self-monitoring of diet and other healthy lifestyle 
changes.  The Boost sequences for each clinical center was characterized as follows: 
• The four session restart program was offered over a period of 4-8 weeks 
• A new sequence was offered in the Spring and Fall of each year 
• The program was conducted in groups of approximately 10-20 participants 
• Approximately 1-3 groups were conducted during each Spring and Fall sequence, 
as necessary at each clinic to accommodate the former ILS participants 
Centers were encouraged to help participants who have been working primarily in 
intensive, individual lifestyle treatment to make the transition to the group Boost sessions.  

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However, if staff were available, they were permitted to conduct individual visits, mailings, 
and/or phone calls to support lifestyle participants in making this transition to group intervention.  
Topics and lesson materials, handouts, and homework assignments to be utilized in Boost were 
developed by the Lifestyle Resource Core and are in the Lifestyle Intervention Manual of 
Operations for DPPOS.  The first Boost session began within 2-3 months after DPPOS began.   
Boost sessions will not continue in DPPOS Phase 3, but will be replaced, in the former 
lifestyle intervention group only, with a brief, annual lifestyle checkup, a 10-15 minute review of 
lifestyle goals and success. 
 
6.2.5. Indices of Adherence 
 
Adherence to the HELP program and Boost were assessed in the following manner: 
• Group contacts were recorded primarily to assess attendance at both HELP 
sessions and Boost visits  
• Adherence to the 7% weight loss goal was determined from measured body 
weight at mid-year and annual clinic visits for all participants  
• Weight data and self-reported physical activity minutes were collected at the 
Boost sessions  
• Performance of physical activity was determined from interviewer administered 
questionnaires that assess physical activity at annual clinic visits for all 
participants 
6.3. 
Lifestyle Program in DPPOS Phase 3  
 
The lifestyle program for DPPOS Phase 3 for visit years 13-18 will consist of an annual 
lifestyle check-up for participants originally randomized to the intensive lifestyle group, a 10-15 
minute review of lifestyle goals and success, and an annual HELP session for all participants to 
promote retention and reinforce healthy lifestyle lessons. 
 
6.4. 
Metformin Pharmacological Treatment 
 
6.4.1. Description of Intervention 
 
The pharmacological intervention is metformin 850 mg bid, as tolerated.  DPP 
participants who had been randomized to active metformin and are still eligible to take 
metformin will remain in the metformin arm of the follow up study.  This will allow the longest 
possible period of continued exposure to metformin to determine its longer-term effects.  
Participants who are not eligible to continue study-supplied metformin are those who 
cannot tolerate metformin, whose eGFR is below 30 mL/minute/1.73 m2, who reached the 
fasting hyperglycemia (≥140 mg/dL) outcome during DPP, who have been taken off metformin 
for other medical reasons, and/or those who have diabetes and whose HbAlc was measured ≥7% 
by the DPPOS Central Biochemistry Laboratory.  Metformin is an investigational drug used 
under an Investigational New Drug application with the Food and Drug Administration (FDA) 
(IND #142797).  

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6.4.2. Mechanism of Metformin Action 
 
Metformin is an antihyperglycemic drug of the biguanide class used in the management 
of Type 2 diabetes worldwide for over 50 years.  It was approved for use in the U.S. in 1995 and 
is distributed by Bristol Myers-Squibb under the trade name Glucophage, and manufactured and 
provided to DPPOS by Merck KGaA, Darmstadt, Germany.  Generic products are now available 
as well. 
Metformin reduces the excess hepatic glucose production that characterizes Type 2 
diabetes without increasing insulin secretion.  With reduced hyperglycemia, glucose uptake by 
muscle and other insulin sensitive tissues is enhanced while insulin levels remain stable or 
decline.  In addition to its antihyperglycemic action, metformin also has antihyperlipidemic 
effects; particularly the lowering of serum triglyceride levels and is associated with weight loss. 
  Metformin has been found to cause lactic acidosis rarely (about 0.03 cases per 1,000 
person years) and then only when used in persons with renal or hepatic insufficiency or during 
episodes of hypoxia or circulatory failure. 
Before its 1995 release in the U.S., and after review of extensive metformin use in 
Canada, Europe and other parts of the world, Bristol-Myers Squibb issued an FDA approved 
package insert providing detailed contraindications, precautions and safety monitoring 
recommendations for its use in T2DM.  During the DPP all of these recommendations (including 
periodic assessment of serum creatinine) were strictly adhered to and the maximum dosage used 
(1.7 gm/day) was less than the maximum recommended (2.55 gm/day). 
Metformin is not currently approved for use as a preventive medication for the 
development of T2DM.  However, the DPP demonstrated that metformin is effective in persons 
with impaired glucose tolerance, reducing the development of diabetes by 31%. 
The most common side effects associated with metformin are gastrointestinal.  As many 
as 30% of persons report diarrhea, nausea, metallic taste, abdominal bloating, flatulence or 
anorexia.  These symptoms are generally transient, resolve spontaneously and can be avoided by 
gradual escalation of dosage.  Metformin is not associated with hypoglycemia unless used in 
conjunction with other glucose-lowering medications (sulfonylurea or insulin).  About 4% of 
participants were unable to continue metformin in U.S. clinical trials. 
About 6-9% of persons on metformin develop reduced vitamin B12 levels.  However, 
megaloblastic anemia is rare and metformin use has not been reported to cause peripheral 
neuropathy. 
 
6.4.3. Dosing Schedule and Restarts 
 
Administration of metformin will be 850 mg twice each day, taken with food, and with 
doses recommended to be at least eight hours apart.  
If a participant has a lapse in treatment due to illness, hospitalization or other cause and is 
eligible to restart the medication, then a plan for restart and titration should be considered.  This 
plan should be based on clinical judgment taking into account the amount of time off metformin 
and the individual’s history of side effects.   
 
6.4.4. Safety Monitoring and Measures to Reduce and Manage Potentially Drug related 
side Effects 

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A. 
Laboratory Safety Monitoring 
During DPPOS Phases 1 & 2, all participants assigned to open label metformin had an 
annual CBC with differential count and serum creatinine.  During DPPOS Phase 3, serum 
creatinine will be measured annually and eGFR calculated, and, in years 14 and 16, vitamin B12 
levels will be measured, in participants taking study metformin. Women in the metformin 
treatment group will be asked to get immediate pregnancy testing if their menstrual cycles are 
more than one week overdue or they otherwise suspect they are pregnant.   
B. 
Potential Non-Gastrointestinal Side Effects 
Potential non-gastrointestinal side effects include, but are not limited to: headache, mild 
edema, leg cramps, arthralgia, myalgias, dizziness, mild rashes, and dysmenorrhea.  If non-
gastrointestinal side effects considered likely to be due to metformin occur and require cessation 
of metformin, it will be stopped for four weeks.  If the non-gastrointestinal symptoms disappear, 
a second attempt to introduce medications is made after the four weeks.  If symptoms re-occur, 
the metformin will again be discontinued.  Clinical judgment should be used to decide 
continuing attempts.  The plan for restart and titration of metformin is based on clinical judgment 
taking into account the amount of time off metformin and the individual’s history of side effects.  
The Manual of Operations includes required steps for restart.   
C. 
Discontinuation of Metformin Use During Hospitalizations 
Metformin should not be used in patients with hypoxia or circulatory failure and should 
be discontinued before the administration of contrast dyes and surgery requiring general 
anesthesia.  To avoid having metformin administered inadvertently to hospitalized participants in 
whom it may be contraindicated, medication will be discontinued during hospitalizations. 
Testing of glucose tolerance for DPPOS will be delayed until medication has been resumed for at 
least two weeks.  However, glucose tolerance testing will be performed within 6 weeks even if 
medication has not been restarted, assuming that the subject does not have a concomitant 
condition that substantially interferes with glucose tolerance.  If the participant has a serious 
condition (e.g., recovering from major surgery, on high doses of steroids, ongoing febrile 
illnesses) known to affect the glucose tolerance adversely, the testing will be postponed until the 
next regularly scheduled testing of glucose tolerance.  Participants will have an OGTT or FPG at 
least annually. 
D. 
Gastrointestinal Symptoms 
These symptoms include diarrhea, abdominal pain, vomiting, nausea, a metallic taste, 
bloating, flatulence and anorexia. If these symptoms are mild and tolerable, medications will be 
continued.  If they are moderate or difficult to tolerate, they will be presumed initially to be due 
to metformin and metformin will be withheld, at least temporarily.  In the event that diarrhea, 
abdominal pain or vomiting becomes severe enough to cause dehydration or volume depletion, 
metformin will be discontinued immediately and the participant will be evaluated and treated 
appropriately.   
E. 
Renal Insufficiency 
Serum creatinine safety measurements will be made yearly and eGFR calculated in 
participants in the metformin arm who are taking study metformin.  Metformin is not known to 
cause renal insufficiency.  However, it is associated with an increased risk for lactic acidosis if 
used in persons with reduced kidney function. Metformin is contraindicated in those with eGFR 
<30 mL/minute/1.73 m2, and should be used with caution and reviewed in those with eGFR ≥30 
and <45 mL/minute/1.73 m2.  If eGFR levels are <30 mL/minute/1.73 m2, study-supplied 

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metformin will be discontinued permanently.  For participants who have an eGFR ≥30 and <45 
mL/minute/1.73 m2, the local PI can elect to continue metformin or stop it based on clinical 
judgment that takes into account the cause of renal dysfunction, anticipated clinical course and 
other factors. An interim serum creatinine measurement and calculated eGFR can be requested 
for safety monitoring.   
F. 
Anemia 
During DPPOS Phases 1 & 2, a CBC was measured for safety reasons at yearly intervals 
in participants in the metformin treatment group who were taking study metformin.  If anemia 
(defined as a hematocrit < 36.0% in men and < 33.0% in women) or significant macrocytosis 
develop, or if the hematocrit decreases by 4 or more points from the level at study entry (e.g., 
from 44% to 40%) the participant and primary care provider will be notified.  Medication may be 
continued if the cause of the anemia is identified and treated.  This includes the administration of 
vitamin B12 when indicated.  The annual CBC will be replaced by B12 measured in years 14 and 
16 for those taking study metformin. 
G. 
Pregnancy and Nursing 
Female DPPOS participants of childbearing age who are fertile have been informed of 
the potential risks to a pregnancy conceived while on metformin treatment.  These women will 
be asked to practice reliable birth control including systemic hormones, intrauterine devices or 
barrier methods (diaphragm, male or female condom, cervical cap) with concomitant 
intravaginal spermicide. 
Women in the metformin treatment group will be asked to get immediate pregnancy 
testing if their menstrual cycles are more than one week overdue or they otherwise suspect they 
are pregnant.  If a woman plans to become pregnant or becomes pregnant, metformin will be 
discontinued.  Following the pregnancy and nursing, metformin will be restarted with 
consideration of titration from one 850 mg tablet to two tablets over four weeks.  See the 
Protocol Section 7.1 for more details about metformin use following pregnancy. 
H. 
Radiological Studies Using Contrast Dyes 
Because of the potential danger of contrast induced renal insufficiency and lactic acidosis 
associated with metformin, under these conditions, the last dose of medication will be 
administered on the day prior to administration of contrast dyes.  Serum creatinine level will be 
checked 48 hours or more after dye administration. Metformin will be re-started if the eGFR is in 
the acceptable range (≥30 mL/minute/1.73 m2).  A wallet ID will be given to all participants and 
a warning letter will be sent to all primary care providers to alert them to the fact that participants 
are taking metformin and that metformin needs to be discontinued prior to any radiological 
studies involving contrast dyes. 
I. 
Lactic Acidosis 
Metformin may rarely be associated with the development of lactic acidosis, defined as a 
metabolic acidosis with lactate ≥ 5.0 mM.  If hospitalization or an unexplained metabolic 
acidosis occurs, metformin will be discontinued immediately and not restarted.  The participant 
will be evaluated and treated appropriately. 
J. 
Hypoxic States - Congestive Heart Failure 
States of hypoxia or hypo perfusion, including acute congestive heart failure and acute 
myocardial infarction, may lead to lactic acidosis and require discontinuation of metformin and 
treatment of the underlying condition.  If the underlying hypoxic state is corrected or if CHF is 
transient (for example, after an acute MI), reinstitution of medication may be considered.  
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should have their metformin stopped.  Medication arm participants who develop NYHA 
Functional Class 2 and require a loop diuretic or digitalis should have their metformin stopped. 
K. 
Surgical Procedures 
Because of the risk of metabolic acidosis during general anesthesia and major surgical 
procedures, medication will be suspended prior to such anticipated surgical procedures, with the 
last dose administered on the day prior to surgery. Metformin will obviously be held while 
participants are NPO for procedures.  As part of usual clinical care, serum creatinine should be 
checked 48 hours or more after such procedures and before study metformin is restarted if the 
eGFR is in the acceptable range (>30 mL/minute/1.73 m2). If the clinic is notified of a scheduled 
outpatient surgical procedure, the participant will be instructed to discontinue metformin the day 
prior to the procedure.   
L. 
Dermatological Reactions 
In the event of major dermatological reactions such as generalized urticaria, bullous 
rashes, exfoliative dermatitis or Stevens Johnson Syndrome, medication will be discontinued 
immediately and not restarted.  For localized skin reactions, medication may be discontinued if 
the skin reactions are potentially drug related.  If the rashes clear, medication may be restarted 
after four weeks, starting at the Step I dosage level and then progressing to Step II after another 
four weeks.  If localized skin reactions recur with restarting the metformin, metformin should be 
discontinued.  
M. 
Headaches 
Metformin has sometimes been associated with transient headaches, although not more 
frequently than placebo.  However, headache is not a reason to decrease or discontinue the 
metformin unless severe and no other causes are found. 
 
6.4.5. Indices of Adherence 
 
The goal of the pharmacological treatment is to optimize adherence to the 
pharmacological regimen, while maximizing retention of participants in the DPPOS.  
Assessment of adherence to the prescribed medication will provide clinic staff a means to 
identify participants having problems with adherence. 
The following will assess adherence to the pharmacological treatment: 
• Visual inspection of participant's returned pill containers including a pill count 
estimating the percent of prescribed medication taken.  
• A brief, structured interview, during which the case manager will assist 
participants to identify problems with adherence to metformin and to develop 
strategies to promote adherence, as needed. 

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7. 
DEFINITION AND MANAGEMENT OF CONCOMITANT CONDITIONS 
 
Clinical centers are neither sufficiently staffed nor funded to provide primary care or 
ancillary care to participants involved in DPPOS.  The study recommends that participant health 
issues be followed by a primary care provider. Treatments for concomitant conditions can 
potentially affect either the primary or secondary study outcomes and therefore are carefully 
tracked by the study.  If the participant consents, clinically relevant laboratory and medical 
results are communicated in writing to the primary care provider.  The annual HELP session 
provided to all participants will include reinforcement of healthy behaviors, including smoking 
cessation. 
 
7.1. 
Pregnancy and Contraception 
 
Women with a history of gestational diabetes (GDM) are a substantial subgroup of the 
DPP.  Some of these women, together with other participants in DPP, will be of childbearing 
potential during the course of the DPPOS. Data from available cohorts suggest that about 6 
percent of women of childbearing age may be expected to get pregnant each year. 
Female DPPOS participants of childbearing age who are fertile have been informed of 
the potential risks to a pregnancy conceived while on metformin treatment.  These women will 
be asked to practice reliable birth control including systemic hormones, intrauterine devices or 
barrier methods (diaphragm, male or female condom, cervical cap) with concomitant 
intravaginal spermicide. 
 
7.1.1. Safety Monitoring 
 
Women in the metformin treatment group will be asked to get immediate pregnancy 
testing if their menstrual cycles are more than one week overdue or they otherwise suspect they 
are pregnant. 
 
7.1.2. Use of Study Metformin During Pregnancy and Breast-feeding 
 
Metformin is contra-indicated in pregnancy although data on adverse effects on the fetus 
or the mother are scant.  The embryo toxic effects of biguanides have been evaluated in the in 
vitro cultured mouse embryo model99.  Because of the lack of teratogenicity of metformin in the 
few available studies, this drug is classified by the FDA as pregnancy category B (no evidence of 
risk in humans, animal findings negative).  In recently reported studies, metformin has been 
shown to increase fertility in women with PCOS and some practitioners are investigating 
potential benefits of continuing its use during gestation. In the absence of definitive evidence 
indicating the safety of this practice, we will continue to recommend that during pregnancy and 
for the duration of breast-feeding; metformin should be discontinued in DPPOS participants. 
 
7.1.3. Outcomes Assessment Following Pregnancy 
 
Participants who become pregnant during the DPPOS are likely to develop gestational 
diabetes, and many of these women will require insulin. The standard of care for follow-up after 
gestational diabetes is to assess glucose tolerance at six to eight weeks post-partum. Women who 

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become pregnant during the DPPOS will have outcome assessments suspended until 6-8 weeks 
following delivery. This outcome measure following pregnancy will always be an OGTT.  They 
will then attend the next regularly scheduled outcome assessment visit based on their original 
DPPOS follow-up schedule.  Women meeting ADA criteria for diabetes will have reached the 
DPPOS outcome. 
For those DPPOS participants who require insulin during pregnancy, assessing the 
ongoing need for insulin should begin in the hospital immediately post-partum. Women 
discharged on insulin should be evaluated with home glucose monitoring, followed by their 
providers of obstetrical care, to determine the ongoing need for insulin.  Based upon post-partum 
monitoring, some women may remain on insulin or be started on oral hypoglycemic agents by 
their obstetrical/primary care provider(s).  Participants treated with insulin or oral agents will not 
be re-started on their metformin unless and until their need for therapy resolves. 
There may be some women who are still being treated by their primary care provider(s) 
with insulin or oral agents at the time of their first outcome assessment following pregnancy (i.e., 
6-8 weeks following delivery).  To ensure standardized assessment of outcomes, therapy must be 
stopped for the OGTT.  If cessation of therapy is not possible, two elevated fasting plasma 
glucose determinations may be used to define an outcome of diabetes in place of the OGTT. 
 
7.2. 
Diabetes 
 
7.2.1. Interim Visits for Symptoms 
 
Following enrollment and randomization in the DPPOS, participants will be evaluated on 
a semi-annual basis for assessment of adverse events.  If a participant develops symptoms 
consistent with uncontrolled hyperglycemia, he or she will be instructed to come to the clinical 
center for assessment of an adverse event and undergo a fasting plasma glucose determination.  
This test may be performed locally if needed for safety reasons; however, a sample must be sent 
to the CBL for outcome assessment.  If the centrally read fasting glucose is ≥ 126 mg/dL, a 
repeat test will be performed within 6 weeks to confirm the diagnosis.  The participant will have 
reached the DPPOS diabetes outcome if fasting glucose ≥ 126 mg/dL persists. 
 
7.2.2. Intervention and Follow-up for Participants with Diabetes 
 
Participants, investigators, and primary care providers will be unmasked to the diagnosis 
of diabetes.  The participant and the primary care provider will be informed of the diagnosis and 
the significance will be explained.  Participants will be instructed to follow up with their PCP 
following diagnosis. DPPOS participants will continue to be seen at six monthly intervals during 
years 1-12 and annually beginning in DPPOS year 13 for clinical assessment, and fasting glucose 
and HbA1c determinations will be obtained and sent to the CBL.  Secondary outcome 
measurements will continue to be performed as scheduled. 
All participants will be encouraged to attend the group HELP sessions (annual during 
DPPOS Phase 3) to reinforce the intervention that they have received.  Subsequent individual 
reinforcement of standard lifestyle recommendations will occur at the scheduled annual visits.   
For persons taking study assigned metformin, the investigator, in conjunction with the primary 
care provider, will endeavor to maintain the participant on assigned metformin as long as the 
HbA1c remains <7%.  In the event that a participant progresses to an HbA1c ≥7%, study 

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metformin will be discontinued.  In all participants with diabetes, when the HbA1c is ≥7%, a 
stepped care protocol for treatment of diabetes mellitus, as recommended by the American 
Diabetes Association, will be recommended to the primary care provider.   
 
 
 

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8. 
ADVERSE EVENT REPORTING  
 
8.1. 
Definitions 
 
Only adverse events meeting the criteria for serious will be ascertained and reported to 
the DSMB following FDA guidelines.  Serious adverse events have been defined to include any 
adverse experience that results in any of the following outcomes: 
* Death 
* A life-threatening adverse experience 
* Overdose to any medication 
* Inpatient hospitalization or prolongation of existing hospitalization 
* A permanent or severe disability 
* A congenital anomaly/birth defect 
* Important medical events that do not result in death, are not life-
threatening, and/or do not require hospitalization will be considered as 
serious if, based on appropriate medical judgment, they jeopardize the 
participant and would require medical or surgical intervention to prevent a 
serious adverse event. 
 
8.2. 
Eliciting and Recording Serious Adverse Events 
 
Reporting of serious adverse events will be accomplished by collecting information on 
these adverse experiences during annual, semi-annual and interim follow-up visits. In order to 
avoid bias in eliciting serious adverse events, these adverse events will be assessed using a 
standardized checklist based on study outcomes and total body system assessment. 
For all participants, serious adverse events will be assessed semi-annually, as well as 
collected during the interim, as reported.  Serious adverse events will be reported to the 
Coordinating Center as they occur through routine data entry (within 2-3 days), with the 
exception of death or other life threatening and unexpected adverse events.  All deaths or other 
life threatening and unexpected adverse events, regardless of intervention assignment, must be 
reported to the Coordinating Center within 24 hours of clinic notification. The Coordinating 
Center will transmit the death report to the NIDDK Program Official. 
For participants assigned to the metformin treatment group, the NIH-NIDDK must 
provide a written report of all serious and unexpected adverse events to the Food and Drug 
Administration (FDA) in their annual IND report.  In addition, the NIDDK must notify the FDA 
of all life-threatening or fatal SUSARs (Serious Unexpected Suspected Adverse Reaction) within 
seven calendar days; NIDDK must notify the FDA of all other SUSARs by 15 calendar days.  
 
All serious adverse events will be reported to local IRBs by the clinic following 
individual institutional guidelines. 

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9. 
DATA PROCESSING 
 
9.1. 
Data Forms 
 
DPPOS data forms are completed to document protocol performance and to collect 
participant data relevant to the research questions.  The section that follows outlines each type of 
data form that is used to collect participant data and is contained in the master database 
maintained by the Coordinating Center (CoC).  Chapter 12 is the schedule of outcomes 
collection.  The list of DPPOS data forms appears in the study Manual of Operations, and 
includes administrative as well as data collection instruments. 
The CoC creates the DPPOS data form templates.  At each clinic, the clinic staff, directed 
by the program coordinator, reviews completed data forms prior to data entry.  Completed forms 
are edited as they are entered into the data management system, and then again via the central 
data management system at the CoC. 
• Follow-up visit inventories: 
Completed according to the schedule in Chapter 12: serious adverse event assessment, 
diabetes management, current concomitant prescription medications, interval medical history 
and interval cardiovascular history, neuropathy screening, and physical measures; and for the 
metformin treatment participants, pregnancy questions, and medication compliance and 
dispensing.  In addition, outcomes outlined in Chapter 4 are completed according to the 
schedule in Chapter 12.  
• Interim follow-up visit inventory: 
Reason for interim visit, serious adverse event assessment, interval history, pregnancy 
questions, and for metformin treatment participants, medication compliance and dispensing. 
• Missed follow-up visit report: 
Completed anytime a participant misses a scheduled follow-up visit: reason for missed visit 
and inactive follow-up status. 
• Home and phone visit report; 
Completed for outcome visits: serious adverse event assessment, interval history, current 
concomitant prescription medications, and physical measures (as appropriate); and for the 
metformin treatment participants, pregnancy questions, and medication compliance and 
dispensing. 
 
9.1.1. Other Forms 
 
The following instruments were completed during DPPOS Phases 1 & 2, or will be 
completed during DPPOS Phase 3, according to the schedule in Chapter 12: 
 
 Beck Questionnaire 
 MOS SF-36 Health Survey Questionnaire 
 Modifiable Activity Questionnaire 
 Nutrition Interview 
 Resource utilization for participants 
 Interval History Questionnaire 
 Quality of Well-Being Scale 
 Urinary Incontinence Questionnaire 

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 Neuropathy Questionnaire 
 Dietary Restraint, Exercise Self-Efficacy, Low Fat Diet Self-Efficacy 
 Cognition questionnaires  
 Physical functioning:  Grip strength, Gait Speed, Chair Stand, Balance 
 Cancer history and risk factor questionnaire 
 Activities of Daily Living (ADL) and Instrumental Activities of Daily Living 
(IADL) 
 Sexual Function Questionnaires  
 6-Minute Walk Test Questionnaire  
 
The following event data forms are completed as needed: 
 
 Adverse event reports 
 Diabetes confirmation report  
 Pregnancy confirmation and outcomes reports 
 Mortality report 
 
The following procedure worksheets collect participant status or physical 
information (see Chapter 12 for timing and frequency of procedures): 
 
 OGTT procedures 
 Urine collection procedures 
 ECG procedures 
 Fundus photography and Optical Coherence Tomography (OCT) procedures 
 Coronary artery calcium procedures  
 DXA procedures  
 Spirometry procedures 
 
The following report data forms are completed as needed: 
 
 CHD Risk Status Report 
 Consent and specimen status 
 
9.2. 
Data Entry and Management System 
 
9.2.1. Clinical Centers 
 
A secure, web-based password protected data entry and management software 
corresponding to the data forms completed at a clinical center is developed and maintained by 
the staff at the Coordinating Center (CoC).  Reports are developed for use at the clinical centers 
to assist clinical center staff in participant management, data collection and study management.  
DPPOS computers are kept in a safe location in a site that is locked when not attended.   
 
 
 
 

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9.2.2. Central Biochemistry Laboratory 
 
The Central Biochemistry Laboratory (CBL) uses a relational database to manage 
analyses performed within the laboratory using a custom-developed Laboratory Information 
Management System (LIMS).  Automated analyzers are connected to the database via 
communication interfaces developed and maintained by the CBL staff.  Reports to the CoC are 
transmitted via secure FTP to the CoC with the original reports stored in the relational database 
as well as on a file server.  All storage media containing clinical data in use at the laboratory 
utilize hardware fault redundancy and the data are backed up daily to a secure and remote data 
storage facility.          
                                                          
9.3. 
Centralized Data Management System 
 
 
Data entered via the web-based electronic data collection system is securely transmitted 
and stored on the CoC’s server.  Data are converted to SAS data sets after being uploaded to the 
CoC’s server.  All new data are edited for unavailable, out of range, or inconsistent values.  
Weekly audit programs produce more detailed edits across forms for an individual participant.  
Summaries are prepared for reports to the Steering Committee and Protocol Oversight Program. 
The CoC maintains confidentiality of patient data and emerging results per a confidentiality 
policy, which every staff member is required to sign. 
The CoC adheres to the Biostatistics Center’s data backup and security policies to ensure 
the safety and confidentiality of the data.  Backup procedures include: twice-weekly system 
backup, daily incremental back-up, and off-site disaster recovery backup.  Security procedures 
include: logon and link password protection, and for internet access, separate Web servers which 
use SSL and encryption algorithms.  Virus and malware protection software is used on all 
computers and is updated on an hourly basis. All portable computers employ full disk 
encryption. University computing facilities provide support in the event of a disaster.  Access to 
the server and databases is secured by use of login user accounts and passwords.  Remote access 
is granted only to authorized users and is accomplished using a secure virtual private network 
(VPN).  Appropriate filtering/firewall setup is used to prevent unauthorized access. 
 
9.4. 
Performance Monitoring 
 
9.4.1. Training Workshop and Site Visits 
 
The CoC, and Central Units, with appropriate investigator subcommittee members, have 
established procedures to train and certify clinical investigators in the protocol, manual of 
operations, and data processing procedures.  Workshops are held for training personnel from the 
clinical centers to address the appropriate DPPOS procedures including the use of the DPPOS 
data forms and data processing systems.  CBL personnel instruct the program coordinators on 
proper collection, packaging and mailing of specimens for analysis by the CBL.  Central units 
also instruct, train and certify the program coordinators and technicians (as needed) to promote 
standard assessments. The CoC will maintain close contact with the program coordinators and 
will provide additional training or review as needed. 
Based on clinic performance monitoring, appropriate representatives from the CoC, the 
NIDDK, and clinic investigators will visit the clinical centers virtually or in person, as required.  

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These site visits will review procedures with the program coordinators/technicians, assess 
proficiency in executing the DPPOS protocol, review deficiencies detected in monitoring the 
performance of the clinical centers, review the utilization of personnel relative to the amounts 
budgeted, and receive feedback on the adequacy of the centralized support operations. 
 
9.4.1.1. Periodic Performance Reports 
 
During the DPPOS, the CoC will monitor the performance of the clinical centers and 
produce periodic reports summarizing protocol performance for the Protocol Oversight Program 
(POP) committee. 
 
9.4.1.2.  Retention 
 
The CoC and the POP will monitor the performance of the clinical centers in retaining 
participants.  The CoC will also prepare monthly reports on participant compliance with the 
DPPOS protocol and participants on inactive follow-up. 
 
9.4.1.3.  DPPOS Data Form Completion 
 
The CoC will prepare periodic reports presenting tabulations for data completion and 
quality.  Missing data, particularly on outcome variables, will effectively reduce the power of 
analyses.  In fact, systematic patterns of missing data could bias the study results.  Therefore, 
many of the procedural details outlined in the Manual of Operations are designed to minimize 
the amount of missing data. 
 
9.4.1.4.  Other Reports 
 
Other reports will be developed, as needed, based on requests from the Steering 
Committee and associated subcommittees. 
 
9.5. 
 Interim Statistical Reports 
 
Interim reports to the Data and Safety Monitoring Board (DSMB) will include adverse 
events by treatment group, study progress, major issues considered and decided by the Steering 
Committee, protocol modifications, ancillary studies approved, protocol compliance, and data 
quality.  Highlights of completed analyses related to study papers will be presented as they 
become available.  During DPPOS Phase 2, there were two formal interim analyses of safety and 
efficacy pertaining to macrovascular events for purposes of possible "early stopping" of an 
intervention. The DSMB will develop a safety monitoring plan for DPPOS Phase 3 to include a 
futility assessment. 
 
 

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10. 
STUDY ADMINISTRATION 
 
10.1. Organizational Units 
 
10.1.1. Clinical Centers 
 
Each of the participating clinical centers has agreed to implement the DPPOS Protocol.  
The clinical centers will follow participants according to protocol; assume responsibility for the 
completion of the protocol for each participant enrolled in the study; record participant data 
related to the above; review and enter information from data forms using the data entry and 
management system; and respond to edit queries from the Coordinating Center (CoC).  Each 
clinical center has a Principal Investigator, a Program Coordinator, and additional staff to carry 
out the protocol. 
 
10.1.2. Coordinating Center 
 
The Coordinating Center (CoC) is responsible for all aspects of biostatistical design, 
analysis, data processing and study communications of the DPPOS.  In collaboration with the 
Steering Committee, the CoC is responsible for editing and document processing of the protocol 
and Manual of Operations and data collection forms development and testing.  The CoC provides 
protocol performance monitoring data, and conducts the interim and final statistical analyses.  
The CoC collaborates with the Steering Committee members in the preparation of publications 
based on study results. 
Central resource units include the Central Biochemistry Laboratory (CBL), Nutrition 
Coding Center (NCC), ECG Grading Center (ECG), Fundus Photo Reading Center (FPRC), 
Quality of Well Being Coding Center (QWB), Coronary Artery Calcium Reading Center, 
Cognition Center, DXA Reading Center and DPPOS Central Genetics Core.  Other than the 
Genetics Core and the Cognition Center, these units function as subcontracts to the CoC.  Each is 
required to be in compliance with its IRB and institutional requirements for human subjects 
protection and HIPAA.  They establish and provide baseline and/or repeated measures of study 
outcomes as described in Chapters 5 and 12.  Quality control systems are established for these 
centrally performed assessments and reports will be furnished periodically to the Research 
Group.  In addition, the units will lend expertise to help formulate the protocol and detailed 
procedures for participant preparation, specimen and record labeling, handling and shipping.  
Secure communication systems are maintained for data transfer to the Coordinating Center. 
 
10.2. Funding Mechanism/Study Resources 
 
The DPPOS is supported by the National Institutes of Health through the National 
Institute of Diabetes and Digestive and Kidney Diseases, other co-funding NIH Institutes and 
Centers, and other DHHS co-funding Agencies.  All support to the clinical centers and the 
Coordinating Center will be provided through the NIDDK using the mechanism of the 
Cooperative Agreement. 
The NIDDK program official and project scientist will provide program involvement as a 
participant in the scientific efforts of the DPP Research Group through development of protocols 
and assistance in the conduct of the DPPOS. 

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10.3. Working Committees 
 
10.3.1. Steering Committee and Subcommittees 
 
The Steering Committee (SC) is the representative body of the research group.  The 
Committee consists of the Principal Investigator from each clinical center, CBL and the CoC, 
and the NIDDK Project Scientist.  This committee is the policy and decision making group, and 
will oversee the administrative aspects of the DPPOS Research Group.  It provides overall 
scientific direction through consideration of recommendations from the subcommittees and 
Executive Committee.  The committee will approve the details of study design and all procedure 
manuals and participant management policies.  The SC will monitor protocol adherence at the 
clinical centers including proper data generation, recording and transmittal.  Members unable to 
attend a meeting may designate an alternate to act on their behalf.  The members of the Steering 
Committee select the Study Chairperson and Vice-Chairperson. 
Steering Committee recommendations for changes in the Protocol require prior 
consideration by the appropriate subcommittee or Planning Committee, and an affirmative vote 
by two-thirds of the Steering Committee members present and voting. 
Although the Steering Committee is the decision and policy-making group of the 
DPPOS, a smaller group has been appointed to direct day-to-day activities.  This Executive 
Committee consists of the Chair of the Steering Committee, the Vice-Chair of the Steering 
Committee, the Chair of the Publications and Presentations Committee, 1 or 2 Principal 
Investigators from the clinical centers, representatives of the Study Coordinators, the NIDDK 
Project Scientist and Program Official, and the Principal Investigator(s) and Project Coordinator 
of the CoC.  The committee meets by telephone conference, as necessary, and generally on a 
weekly basis.  Other members of the Steering Committee, such as chairs of Sub-Committees, are 
asked to attend the weekly conference call on a regular basis and as needed to address specific 
issues.  
Subcommittees comprise members of the research group.  Their function is to develop 
detailed policies and procedures and make recommendations to the Steering Committee.  During 
DPPOS the subcommittees will be reformed and new subcommittees and working groups 
formed, as necessary to address different tasks and functions. 
Standing DPPOS Subcommittees: 
* Ancillary Studies 
* Economic Evaluation Workgroup 
* Outcomes Classification 
* Program Coordinator 
* Protocol Oversight Program 
* Publications and Presentations 
* Quality Control 
 
10.3.2. Data and Safety Monitoring Board 
 
The Data and Safety Monitoring Board (DSMB) members serve as external reviewers 
and advisors to the NIDDK-NIH and the Steering Committee.  The DSMB consists of experts in 
relevant biomedical fields, Biostatistics and medical ethics.  Prior to the initiation of the DPPOS 

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and ongoing through all phases of DPPOS, the DSMB members review the protocol and study 
material to ensure the scientific validity of the study and safety of participants.  The DSMB also 
assesses the performance of the CoC and clinical centers.  Its principal responsibility is to 
monitor the emerging results to assess treatment effectiveness, or ineffectiveness, and participant 
safety according to the DSMB-approved interim monitoring plan.  Based on these 
considerations, the DSMB may recommend to the NIDDK that the protocol be modified or that 
the study be terminated. 
 
10.4. Policies 
 
10.4.1. Publications 
 
The Publications and Presentations Subcommittee (PPS) coordinates, monitors, reviews, 
and assumes responsibility for arranging the preparation of all study-wide communications 
(press releases, interviews, presentations, and publications) relating to the scientific aspects of 
the study.  There will be no publication or presentation of study plans or results which have not 
been reviewed and approved by a majority of the PPS, and for some types of communications, a 
majority of the Steering Committee. 
With respect to publications and presentations from the DPP, the goals of the PPS are to: 
1.  Ensure accurate, uniform, timely, and high quality reporting of the DPP activities and 
results; 
2.  Preserve the scientific integrity of the study; 
3.  Safeguard the rights and confidentiality of participants; 
4.  Assure that the timing of publications and presentations serves the right of the public 
to know the results of the program without jeopardizing its conduct. 
The PPS will organize a writing group for each publication or presentation proposed by 
the DPP investigators.  Members of the writing group will include volunteers from the DPP 
investigators at large, and will not be restricted to members of the PPS.  The PPS will coordinate 
the efforts of the writing group, establish priorities for data analysis by the Coordinating Center, 
and help edit the manuscripts produced by the writing groups. 
There will be several categories of publications and presentations, with different rules for 
authorship, ranging from publications of the main results of the study (with authorship by the 
entire research group) to other types of publications with named authors.  The authorship rules 
balance the need to recognize the contributions of all investigators and staff with the need to 
recognize individuals for specific contributions to certain types of publications and presentations.  
Detailed policies are found in the Manual of Operations. 
 
10.4.2. Ancillary Studies 
 
The Ancillary Studies Subcommittee evaluates all proposals for studies that involve 
DPPOS participants or stored samples and that are not a part of the protocol.  These studies may 
be done only on a subset of participants in the DPPOS.  However, studies that include all 
participants and studies that analyze study data in ways extracurricular to the Protocol must also 
be submitted to the Ancillary Studies Subcommittee.  Ancillary studies have to obtain funding 
from outside the study. 
Major factors in consideration of ancillary studies will include: 

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* Clinical importance and scientific validity 
* Compatibility of goals with those of DPPOS 
* Amount of burden on study subjects and staff 
 
Ancillary studies receive a primary, secondary and statistical review.  An outside 
reviewer may be used if there is no expertise within the study in a specific area.  Reviews are 
returned to the applicant and appeals from the decision of the Ancillary Studies Subcommittee 
may be made to the Steering Committee.   
Approved ancillary studies that involve participants are reviewed by the DSMB. 
Detailed policies are found in the Manual of Operations. 
 

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11. 
STATISTICAL CONSIDERATIONS 
 
11.1. Data Relevant to the Diabetes Outcome 
 
After approximately 2.8 years of mean study time, the DPP’s external Data and Safety 
Monitoring Board and sponsoring institute, the NIDDK, concluded that the DPP had 
convincingly demonstrated that the intensive lifestyle intervention and metformin therapy 
decreased the development of diabetes. Compared with placebo, intensive lifestyle and 
metformin reduced the development of diabetes by 58% and 31%, respectively.  Both results 
were highly significant and lifestyle was significantly more effective than placebo6. The 
therapies were effective across all ethnic and racial groups and in men and women. The intensive 
lifestyle intervention cohort achieved the target goal of 7% mean weight loss and at least 150 
min of activity per week at year 1. The hazard rates for development of diabetes were:  placebo 
11.0, metformin 7.8, and lifestyle 4.8 per 100 person-years. 
At the end of DPP, 99.6% of the study cohort was alive. The entire cohort proved to be 
remarkably compliant, with 94% retention of volunteers over time, and completion of > 90% of 
study requirements. Adherence (>80% of assigned medication) to metformin was 72%.  
 
11.2. Study Power 
 
11.2.1. Power for the Development of Diabetes  
 
The duration of follow-up in the first five years of DPPOS was extended by one year 
from 5 to 6 years, by NIDDK.  Power calculations were modified based on actual enrollment, 
and to correspond to the reordering of outcome measures.   
 
The following assumptions were used to make revised estimates of the power of the 
DPPOS for the Phase 1 primary outcome, development of diabetes: 
* The study will enroll approximately 900 participants per treatment group 
* The Phase 1 primary outcome is time to the confirmed development of diabetes assessed 
from DPP randomization through DPPOS Phase 1. 
* Type I error rate of 0.05 (two-sided) with a Bonferroni adjustment for two pair-wise 
comparisons of the intervention groups vs. “control”. 
* Control (formerly placebo) group’s time to the development of diabetes is exponentially 
distributed with a diabetes development hazard rate of at least 0.066 per year.   
* In the intervention groups (i.e., intensive lifestyle or metformin), the diabetes development 
hazard rate is reduced by at least 30%. 
* 84% participation of DPP participants in the follow-up study and a dropout rate of not more 
than 2%/year.   
For the comparison of lifestyle vs. control, assuming a type 1 error .025 and a 2-sided 
test, the study will have 84% power to detect a 35% reduction in the hazard rate for development 
of diabetes and 94% power to detect a 40% reduction.  For the comparison of metformin vs. 
control (type 1 error .025, 2 sided test), the study will have 82% power to detect a 35% reduction 
in hazards.   
 
 

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11.2.2. Power for the Microangiopathy Outcome, Year 11  
 
For the composite microangiopathic Phase 2 Primary outcome at year 11, assuming 
N=850 remaining participants per group and 1% per year dropout, and applying the resulting 
numbers of participants expected to develop diabetes during the follow-up study, we estimate the 
power of the study to be 91 percent or greater to detect 25% or greater reductions for each 
intervention from the control group proportion with the microangiopathic outcome, and 74% 
power to detect 20% reductions, using 2-sided pair-wise comparisons vs. placebo with  α=0 .025. 
 
11.2.3. Power for Cancer Development  
 
For the cancer outcome for DPPOS Phase 3, we estimated the number of cancer cases 
through the first 5 years of DPPOS Phase 3 using incidence rates based on both SEER100 and 
current DPPOS data.  To detect 28% risk reduction in cancer for the primary comparison of 
metformin vs placebo with 85% power for a 2-sided significance level of 0.05, the study requires 
170 events in the placebo group using a log-rank test.  Assuming an increasing annual incidence 
rate of 1.86% by 2020 and an annual loss to follow-up of 1.04%, the projected 199 events in the 
placebo group will provide 89% power to detect a 28% hazard risk reduction at the end of the 
first 5-year period.  Secondary analysis of the cancer incidence between metformin and placebo 
separately by men and women will be assessed in the second 5-years.  
 
11.2.4. Power for CVD (MACE) Development  
 
The lower rate of CVD events in pre-diabetes than in diabetes has been documented14. It 
is reasonable to assume that our placebo group, all of whom started with pre-diabetes and with 
~56% developing diabetes to date during the course of DPP/DPPOS, will have a CVD event rate 
that is a blend of pre-diabetes and diabetes.  Moreover, our study population has a similar rate of 
treatment of traditional CVD risk factors (e.g., through use of antihypertensive agent and 
statins)7 to that in the general population today. This trend emphasizes the need to use 
contemporaneous external data to project event rates.  
In this light, the most relevant rates of MACE in non-diabetic and diabetic populations, 
including age-specific rates, come from a recent report on 2010 national data8. These data were 
collected during a period when treatment of established CVD risk factors was widespread, and 
therefore represent the background rates expected in our cohort. For all persons surveyed, the 
rate of acute myocardial infarction fell from 8.5 per 10000 person-years in 1990 to 5.7 in 2010. 
Among those aged 45-64 with diabetes the rate in 2010 was 51.3 per 10000 person-years (or 
0.513 per 100 person-years), while those 65-74 had 66.4 and those over 75 had 143.5 events per 
10000 person-years (0.664 and 1.435 per 100 person-years, respectively). These rates are within 
the range of rates that we observed in the Placebo group by DPPOS end (Table 5).   
 
Table 5. MACE Event Rates and Numbers to Date in Placebo Group and Projections 
 
DPP start 
 1997-1998 
DPPOS start 
2002-2003 
DPPOS end 
2014 
5 yr projection 
2020-2021 
10yr projections 
2025 
Event Rate (% per yr) 
0.24 
0.50 
0.70 
1.17 
1.57 
Total number  
 
 
64 
116 
156 
 

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We estimated the age related 2.1 fold increase in annual incidence rates in the next 10 
years using Cox proportional hazards model using attained age as a time dependent covariate. 
This conservative increase is used to project events in the placebo participants of 116 and 156 
after 5 and 10 additional years of DPPOS Phase 3 assuming a 1.04% loss to follow-up per year. 
To detect a 30% hazard risk reduction in MACE incidence in the primary comparison of 
metformin and placebo with 85% power and a 2-sided significance level of 0.05 using a log-rank 
test, we require 145 placebo events.   With the expected 156 events in the placebo group by 
2025, the study will have 89% power to detect a 30% hazard risk reduction. Other important 
secondary comparisons will be lifestyle vs. placebo and metformin vs. lifestyle.  
 
11.3. Analysis 
 
11.3.1. Analysis of Development of Diabetes  
 
The primary objective for DPPOS Phase 1 was to compare the durability of the original 
effect during the DPP, i.e., estimation of the hazard rates for development of diabetes going 
forward among participants who had not developed diabetes during DPP among those who 
enrolled into DPPOS13.  The analysis was based on comparing the hazard rates between the two 
intervention groups (the Intensive Lifestyle and Metformin groups) and the placebo group. The 
primary null hypothesis was that among those who had not developed diabetes by the start of 
DPPOS, the intervention groups did not differ from the controls in the hazard rates for 
development of diabetes over the interval from the beginning of DPPOS.  Reasons for comparing 
across the interval from the start of DPPOS as the primary analysis rather than from the 
beginning of DPP were: 1) we had already published the comparison of the three groups over the 
DPP interval, and any subsequent comparison encompassing that interval would not be an 
independent analysis; and 2) since the interventions were indeed effective over the earlier DPP 
interval, the cumulative incidence curves may have had too much separation from the early DPP 
effects to be able come together again, even if the interventions were not effective over the 
longer term.  The primary analysis from DPPOS baseline did not preclude secondary analyses 
from the beginning of DPP. 
The cohort of participants for this analysis were a subset of the original DPP study 
population, and as such were no longer “randomized”, but rather selected by having survived 
DPP without developing diabetes.  Beyond that selection, each participant was included in the 
group to which s/he was randomly assigned, regardless of compliance with study treatment. The 
number of participants who had not developed diabetes at DPP study end was 870 in the 
metformin group, 951 in the ILS, and 809 in the placebo group.  The primary outcome analysis 
used an overall significance level of α = 0.05 (2-sided). Two pair-wise comparisons between the 
intervention groups and the former placebo group, set at the = 0.025 level, were performed if the 
overall comparison was statistically significant. 
The analysis compared the treatment groups vs. the former placebo group on DPP 
baseline characteristics, and any factors on which they differed were considered for inclusion as 
covariates in the analysis.  The primary analysis was a life-table analysis of the time to 
confirmed development of diabetes.  Modified product-limit life-table estimated cumulative 
incidence curves were calculated for each treatment group and the groups compared using a log 
rank test3.  Participants were considered “administratively censored” if they completed the full 
duration of follow-up without confirmed development of diabetes.  Participants who prematurely 

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discontinued their follow-up visits prior to confirmed development of diabetes were “censored” 
as of their last follow-up visit.  A proportional hazards regression model was used to evaluate 
potential covariates that may modify the time to development of diabetes.  Graphical procedures 
were used to assess the proportionality assumption.  If the proportionality assumption was found 
to be unreasonable then other models such as the accelerated failure time model101,102,102 or the 
proportional odds model103 was used to evaluate the covariates. 
The analysis was also conducted within subgroups (one-way stratification) based on the 
following characteristics: racial/ethnic origin, sex, and age (<45, 45-<60, 60+). 
The primary analyses that focused on the intention-to-treat assignment during DPP 
included all participants in the original DPP placebo, lifestyle and metformin intervention groups 
who enrolled in DPPOS. Since the participants originally assigned to troglitazone only had a 
limited exposure to that intervention, owing to the premature termination of the troglitazone arm, 
and were not included in the primary DPP outcome analyses, they were not included in the 
primary DPPOS analyses. 
 
11.3.2. Composite Outcomes of Microangiopathic and Neuropathic Disease 
 
The analysis of the composite primary microangiopathic outcome at year 11 for DPPOS 
Phase 2, and composite secondary cardiovascular disease outcome was performed in an intent-
to-treat fashion on the DPP groups, as randomized, including participants who have developed 
diabetes. 
For this composite outcome, the objective was to determine the effect of the interventions 
on the proportion of participants experiencing the outcome through follow-up visit year 11.  For 
the composite primary microangiopathic outcome, the groups were compared using the global 
test using general estimating equations (GEE) among DPPOS enrolled participants1. 
The year 11 data for each component was reviewed with respect to being "missing at 
random" before selecting the appropriate statistical methods for missing data.     
 
11.3.3. Analysis of Cancer and MACE Incidence 
 
The primary outcomes for DPPOS Phase 3 are time to the development of cancer (first 5 
years) and major cardiovascular disease (MACE, including non-fatal myocardial infarction and 
stroke, and fatal cardiovascular disease) (second 5 years).  The cohort of participants for these 
analyses includes all participants randomized to the original DPP study.  Each participant will be 
included in the group to which s/he was randomly assigned, regardless of compliance with study 
treatment. Since the participants originally assigned to troglitazone only had a limited exposure 
to that intervention, owing to the premature termination of the troglitazone arm, were not 
included in the primary DPP outcome analyses, and are no longer followed in DPPOS, they will 
not be included in the primary DPPOS Phase 3 analyses.  
The primary comparison will focus on the metformin vs. the placebo group.  The time to 
event analysis uses the date of the first occurrence of the outcomes.  Participants will be 
considered “administratively censored” if they complete the full duration of follow-up without 
confirmed disease.  Participants who died or prematurely discontinue their follow-up visits prior 
to developing the event will be “censored” as of their last follow-up visit – hence, participants 
who did not enroll in DPPOS will be censored as of their last contact during DPP. Separate 

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Kaplan-Meier estimates of cumulative incidence curves are calculated for the three treatment 
groups and will be compared using the log rank test.    
Mortality prior to the development of cancer or MACE is a competing risk event104,105,105. 
Regression models that censor on death provide an estimate of the coefficient effect on the 
underlying cause-specific hazard for the outcome event. If there is a difference between groups 
in overall mortality, we will examine the cumulative incidence functions within groups adjusting 
for death as a competing risk.  
The analysis will also be conducted using subgroups (one-way stratification) to assess 
treatment effect modification  based on the following characteristics: racial/ethnic origin, sex, 
and age at randomization (<45, 45-<60, 60+). 
A proportional hazards regression model will be used to evaluate potential covariates that 
may modify or mediate the time to development of the outcome106.  To allow for model 
misspecification, such as non-proportional hazards, all inferences will be conducted using the 
robust variance estimate107 that provides a valid inference in the presence of such 
misspecification. 
 
11.3.4. Secondary Research Questions 
 
Secondary objectives are to evaluate the long-term effects of DPP interventions on 
selected individual health outcomes.  These are: 
* Further development of diabetes  
* Diabetic retinopathy  
* Diabetic neuropathy 
* Albuminuria  
* Renal failure 
* Macrovascular disease 
* Cardiovascular disease events 
* Subclinical atherosclerosis outcomes 
* Risk factors for cardiovascular disease 
* Amputation in a lower extremity not resulting from major trauma 
* Hospitalizations 
* Physical activity, nutrition, body mass and obesity 
* Dietary and exercise behaviors 
* Physical function 
* Quality of life indices 
* Health care costs 
* Cognitive performance 
* Urinary incontinence 
* Sexual function 
* DXA-derived bone density, body composition and vertebral fractures 
* Pulmonary function 
* Healthy Aging Index 
* All-cause and cause-specific mortality  
 
Other Analyses. Other research questions will examine the clinical course of IGT and 
newly diagnosed diabetes with regard to the development of microvascular, neuropathic and 

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cardiovascular disease and their respective risk factors.  These “epidemiologic” analyses will 
largely be descriptive.  Appropriate statistical methods will be applied to analyze the interactions 
among putative and established risk factors and the development of different outcomes.  In these 
analyses, treatment assignment during the DPP will be considered a covariate. 
The former troglitazone participants who continue in the DPPOS through visit year 6 will 
be included in the "other" outcomes exploring the relationship between incident diabetes and 
determinants of long-term complications of new-onset diabetes and IGT. No research data will 
be collected in this group beginning with protocol version 3.0. 
 
11.4. Monitoring and Timing of Analyses 
 
An external Data and Safety Monitoring Board will review reports of study progress and 
safety regularly throughout the study.  They will alert the NIDDK and the Steering Committee if 
they believe the study should be stopped for reasons of patient safety.   
Because we have already shown both interventions to be effective in delaying or 
preventing diabetes over 3 years, there would be no compelling reason to stop DPPOS for having 
demonstrated further benefit.  The assessment of the composite microangiopathy occurred after 
the year 11 visits.  Therefore, we did not implement a formal statistical monitoring plan for either 
of these outcomes in DPPOS.  The DSMB reviewed two interim analyses of time to 
macrovascular event for safety during DPPOS Phase 2. 
Since the cohort size for DPPOS Phase 3 is fixed, power is driven by the number of 
placebo subjects with an outcome event and the projected effect size. Projections for the placebo 
events assumed an exponential increase in hazard rate for cancer and MACE expressed in terms 
of a growth factor (i.e. ~2-fold increase over 10 years) and based on accumulated DPP/DPPOS 
data and results from recent studies. Given our best estimate of the accumulation of events, and 
using effect sizes of 25 or 30%, we expect to reach the level of required cancer events in the 
placebo group during the first 5-years of DPPOS Phase 3, and the required MACE events in the 
placebo group during the second 5-years of DPPOS Phase 3.

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12. 
OUTCOMES SCHEDULE  
Outcomes Schedule, DPPOS Phase 1: Visit Years 1-6 
Participant DPPOS visit year  
Year 1 
Year 2 
Year 3 
Year 4 
Year 5 
Year 6 
Visit calendar year 
9/1/02-10/31/03 7/1/03-10/31/04 
7/1/04-10/31/05 
7/1/05-10/31/06 7/1/06-10/31/07 7/1/07-10/31/08 
DPPOS funding calendar year 
2/1/03-1/31/04 
2/1/04-1/31/05 
2/1/05-1/31/06 
2/1/06-1/31/07 
2/1/07-1/31/08 2/1/08-1/31/09 
Mid-year or Annual visit 
Mid 
Ann 
Mid 
Ann 
Mid 
Ann 
Mid 
Ann 
Mid 
Ann 
Mid 
Ann 
Glycemia 
 
 
 
 
 
 
 
 
 
 
 
 
Fasting glucose 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
30', 120' glucose++ 
 
X 
 
X 
 
X 
 
X 
 
X 
 
X 
HbA1c ++ 
 
X 
 
X 
 
X 
 
X 
 
X 
 
X 
Insulin Secretion and Sensitivity 
 
 
 
 
 
 
 
 
 
 
 
 
Fasting, 30’ insulin++ 
 
X 
 
X 
 
X 
 
X 
 
X 
 
X 
Inflammatory, clotting and fibrinolytic factors 
 
 
 
 
 
 
 
 
 
 
 
 
Fibrinogen 
 
X 
 
 
 
 
 
 
 
X 
 
 
TPA 
 
X 
 
 
 
 
 
 
 
X 
 
 
CRP 
 
X 
 
 
 
 
 
 
 
X 
 
 
Lipids 
 
 
 
 
 
 
 
 
 
 
 
 
Lipid profile 
 
X 
 
X 
 
X 
 
X 
 
X 
 
X 
Particle size and sub fractions 
 
X 
 
 
 
 
 
 
 
X 
 
 
Kidney Function 
 
 
 
 
 
 
 
 
 
 
 
 
Urine albumin & creatinine 
 
X 
 
X 
 
X 
 
X 
 
X 
 
X 
Serum Cystatin 
 
X 
 
 
 
 
 
 
 
X 
 
 
Serum Creatinine 
 
X 
 
X 
 
X 
 
X 
 
X 
 
X 
History 
 
 
 
 
 
 
 
 
 
 
 
 
Symptoms and Events 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
Physical 
 
 
 
 
 
 
 
 
 
 
 
 
Weight 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
Height 
 
X 
 
 
 
 
 
 
 
X 
 
 
Waist Circumference 
 
X 
 
X 
 
X 
 
X 
 
X 
 
X 
 

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Outcomes Schedule, DPPOS Phase 1: Visit Years 1-6, Continued 
Participant DPPOS visit year 
Year 1 
Year 2 
Year 3 
Year 4 
Year 5 
Year 6 
Visit calendar year 9/1/02-10/31/03 7/1/03-10/31/04 
7/1/04-10/31/05 
7/1/05-10/31/06 7/1/06-10/31/07 7/1/07-10/31/08 
DPPOS funding calendar year 2/1/03-1/31/04 
2/1/04-1/31/05 
2/1/05-1/31/06 
2/1/06-1/31/07 
2/1/07-1/31/08 2/1/08-1/31/09 
Mid-year or Annual visit 
Mid 
Ann 
Mid 
Ann 
Mid 
Ann 
Mid 
Ann 
Mid 
Ann 
Mid 
Ann 
Blood Pressure 
 
 
 
 
 
 
 
 
 
 
 
 
Arm BP 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
ABI 
 
X 
 
 
 
 
 
 
 
X 
 
 
Quality of Life 
 
 
 
 
 
 
 
 
 
 
 
 
Beck 
X 
 
X 
 
X 
 
X 
 
X 
 
X 
 
SF-36 
 
X 
 
 
 
 
 
 
 
X 
 
 
Urinary Incontinence 
 
X 
 
X 
 
X 
 
X 
 
X 
 
X 
Physical Activity and Nutrition 
 
 
 
 
 
 
 
 
 
 
 
MAQ 
 
X 
 
X 
 
X 
 
X 
 
X 
 
X 
Nutrition Intake 
 
X 
 
X 
 
 
 
 
 
X 
 
 
Cardiovascular 
 
 
 
 
 
 
 
 
 
 
 
 
ECG 
 
X 
 
X 
 
X 
 
X 
 
X 
 
X 
Carotid Ultrasound+ 
 
 
 
 
 
 
 
 
 
 
 
 
Eye 
 
 
 
 
 
 
 
 
 
 
 
 
Retinal photography# 
 
X 
 
 
 
 
 
 
 
X 
 
 
Neurologic 
 
 
 
 
 
 
 
 
 
 
 
 
Symptom Assessment 
 
X 
 
X 
 
X 
 
X 
 
X 
 
X 
MNSI with monofilament 
 
X 
 
X 
 
X 
 
X 
 
X 
 
X 
Heart rate variability 
 
X 
 
X 
 
X 
 
X 
 
X 
 
X 
Saved Specimens 
 
 
 
 
 
 
 
 
 
 
 
 
Fasting EDTA Plasma  
 
X 
 
X 
 
X 
 
X 
 
X 
 
X 
 

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Outcomes Schedule, DPPOS Phase 1: Visit Years 1-6, Continued 
Participant DPPOS visit year 
Year 1 
Year 2 
Year 3 
Year 4 
Year 5 
Year 6 
Visit calendar year 9/1/02-10/31/03 7/1/03-10/31/04 
7/1/04-10/31/05 
7/1/05-10/31/06 7/1/06-10/31/07 7/1/07-10/31/08 
DPPOS funding calendar year 2/1/03-1/31/04 
2/1/04-1/31/05 
2/1/05-1/31/06 
2/1/06-1/31/07 2/1/07-1/31/08 
2/1/08-1/31/09 
Mid-year or Annual visit 
Mid 
Ann 
Mid 
Ann 
Mid 
Ann 
Mid 
Ann 
Mid 
Ann 
Mid 
Ann 
Safety Measures 
 
 
 
 
 
 
 
 
 
 
 
 
Serum creatinine 
 
X 
 
X 
 
X 
 
X 
 
X 
 
X 
CBC* 
 
X 
 
X 
 
X 
 
X 
 
X 
 
X 
Serious Adverse event report** 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
Pregnancy## 
 
X 
 
X 
 
X 
 
X 
 
X 
 
X 
Serology 
 
 
 
 
 
 
 
 
 
 
 
 
IA2***, GAD*** 
 
 
 
 
 
 
 
 
 
 
 
 
Other Chemistries 
 
 
 
 
 
 
 
 
 
 
 
 
Relevant biological markers related to the 
pathogenesis of diabetes and its complications 
 
X 
 
 
 
 
 
 
 
X 
 
 
Economic Evaluation 
 
 
 
 
 
 
 
 
 
 
 
 
Resource Utilization 
 
 
 
 
 
 
 
X 
 
 
 
 
QWB 
 
X 
 
X 
 
X 
 
X 
 
X 
 
X 
 
# Fundus photos were obtained in Year 1 or 2 on a subset of diabetic and non-diabetic participants.  Year 5 photos were completed on all participants in the  
  lifestyle, metformin and placebo arms. 
## Pregnancy tests as needed for participants on metformin based on symptoms and menstrual history and measured locally. 
* In the Metformin treatment group on study metformin measured locally.   
**   Serious Adverse events will be collected at Annual, Mid-year and Interim follow-up visits. 
*** Specimen for IA2 and GAD antibodies will be collected at the time of confirmation and will be analyzed for those who converted. 
+ Carotid ultrasounds were collected during the DPP bridge period as a baseline for DPPOS 
++ For diabetic participants: HbA1c is collected at Mid-Year visits; the 30’ insulin and 30/120’ glucose collections are discontinued 
+++ The following outcomes are not obtained for participants in the former troglitazone arm: carotid ultrasound, fundus photographs, other chemistries 
 
 

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Outcomes Schedule, DPPOS Phase 2: Visit Years 7-12 
Participant DPPOS visit year 
Year 7 
Year 8 
Year 9 
Year 10 
Year 11 
Year 12 
Visit calendar year 9/1/08-10/31/09 
7/1/09-10/31/10 
7/1/10-10/31/11 
7/1/11-10/31/12 
7/1/12-10/31/13 
7/1/13-10/31/14 
DPPOS funding calendar year 
2/1/09-1/31/10 
2/1/10-1/31/11 
2/1/11-1/31/12 
2/1/12-1/31/13 
2/1/13-1/31/14 
2/1/14-1/31/15 
Mid-year or Annual visit
Mid 
Ann 
Mid 
Ann 
Mid 
Ann 
Mid 
Ann 
Mid 
Ann 
Mid 
Ann 
Glycemia 
 
 
 
 
 
 
 
 
 
 
 
 
Fasting glucose 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
30', 120' glucose+ 
 
X 
 
X 
 
X 
 
X 
 
X 
 
X 
HbA1c + 
 
X 
 
X 
 
X 
 
X 
 
X 
 
X 
Insulin Secretion and Sensitivity 
 
 
 
 
 
 
 
 
 
 
 
 
Fasting, 30’ insulin+ 
 
X 
 
X 
 
X 
 
X 
 
X 
 
X 
Inflammatory, clotting and fibrinolytic factors 
 
 
 
 
 
 
 
 
 
 
 
 
Fibrinogen 
 
 
 
 
 
 
 
 
 
X 
 
 
TPA 
 
 
 
 
 
 
 
 
 
X 
 
 
CRP 
 
 
 
 
 
 
 
 
 
X 
 
 
Lipids 
 
 
 
 
 
 
 
 
 
 
 
 
Lipid profile 
 
X 
 
X 
 
X 
 
X 
 
X 
 
X 
Particle size and subfractions 
 
 
 
 
 
 
 
 
 
X 
 
 
Kidney Function 
 
 
 
 
 
 
 
 
 
 
 
 
Urine Albumin & Creatinine 
 
X 
 
X 
 
X 
 
X 
 
X 
 
X 
Serum Cystatin 
 
 
 
X 
 
X 
 
X 
 
X 
 
X 
Serum Creatinine 
 
X 
 
X 
 
X 
 
X 
 
X 
 
X 
History 
 
 
 
 
 
 
 
 
 
 
 
 
Symptoms and Events 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
Cancer History and Risk Factors 
 
 
 
 
 
 
 
 
 
X 
 
 
Physical 
 
 
 
 
 
 
 
 
 
 
 
 
Weight 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
Height 
 
 
 
 
 
 
 
 
 
X 
 
 
Waist Circumference 
 
X 
 
X 
 
X 
 
X 
 
X 
 
X 
DXA (body composition measures)+++ 
 
 
 
 
 
 
 
 
 
 
 
X 
 

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Outcomes Schedule, DPPOS Phase 2: Visit Years 7-12, Continued 
Participant DPPOS visit year 
Year 7 
Year 8 
Year 9 
Year 10 
Year 11 
Year 12 
Visit calendar year 9/1/08-10/31/09 
7/1/09-10/31/10 
7/1/10-10/31/11 
7/1/11-10/31/12 
7/1/12-10/31/13 
7/1/13-10/31/14 
DPPOS funding calendar year 
2/1/09-1/31/10 
2/1/10-1/31/11 
2/1/11-1/31/12 
2/1/12-1/31/13 
2/1/13-1/31/14 
2/1/14-1/31/15 
Mid-year or Annual visit 
Mid 
Ann 
Mid 
Ann 
Mid 
Ann 
Mid 
Ann 
Mid 
Ann 
Mid 
Ann 
Blood Pressure 
 
 
 
 
 
 
 
 
 
 
Arm BP 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
ABI ++ 
 
 
 
 
 
 
 
X 
 
 
 
 
Quality of Life 
 
 
 
 
 
 
 
 
 
 
 
 
Beck 
X 
 
X 
 
X 
 
X 
 
X 
 
X 
 
SF-36 
 
 
X 
 
 
 
X 
 
X 
 
X 
 
Urinary Incontinence 
 
X 
 
X 
 
X 
 
X 
 
X 
 
X 
Physical Activity, Nutrition, Behavior, Functional 
 
 
 
 
 
 
 
 
 
 
 
 
MAQ 
 
X 
X 
 
X 
 
X 
 
X 
 
X 
 
Nutrition Intake 
 
 
 
 
 
 
 
 
 
X 
 
 
Dietary Restraint, Exercise Self-Efficacy, Low Fat 
Diet Self-Efficacy 
 
 
X 
 
X 
 
X 
 
X 
 
X 
 
Physical Function tests (Grip strength, CES-D 
Depression, Gait Speed, Chair Stand, Balance) 
 
 
X 
 
 
 
X 
 
 
 
 
 
Cognition 
 
 
 
 
 
 
 
 
 
 
 
 
Cognitive Function tests 
 
 
X 
 
 
 
X 
 
 
 
 
 
Cardiovascular 
 
 
 
 
 
 
 
 
 
 
 
 
ECG 
 
X 
 
X 
 
X 
 
X 
 
X 
 
X 
Coronary Artery Calcium ++ 
 
 
 
 
 
 
 
X 
 
 
 
 
Eye 
 
 
 
 
 
 
 
 
 
 
 
 
Retinal Photography ++ 
 
 
 
 
 
 
 
 
 
X 
 
 
Neurologic 
 
 
 
 
 
 
 
 
 
 
 
 
Symptom Assessment 
 
X 
 
X 
 
X 
 
X 
 
X 
 
X 
Modified MNSI including monofilament 
 
X 
 
X 
 
X 
 
X 
 
X 
 
X 
Heart rate variability 
 
X 
 
X 
 
X 
 
X 
 
X 
 
X 
 

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Outcomes Schedule, DPPOS Phase 2: Visit Years 7-12, Continued 
Participant DPPOS visit year 
Year 7 
Year 8 
Year 9 
Year 10 
Year 11 
Year 12 
Visit calendar year 9/1/08-10/31/09 
7/1/09-10/31/10 
7/1/10-10/31/11 
7/1/11-10/31/12 
7/1/12-10/31/13 
7/1/13-10/31/14 
DPPOS funding calendar year 
2/1/09-1/31/10 
2/1/10-1/31/11 
2/1/11-1/31/12 
2/1/12-1/31/13 
2/1/13-1/31/14 
2/1/14-1/31/15 
Mid-year or Annual visit 
Mid 
Ann 
Mid 
Ann 
Mid 
Ann 
Mid 
Ann 
Mid 
Ann 
Mid 
Ann 
Saved Specimens 
 
 
 
 
 
 
 
 
 
 
 
 
Fasting EDTA Plasma (no serum is stored) 
 
X 
 
X 
 
X 
 
X 
 
X 
 
X 
Safety Measures 
 
 
 
 
 
 
 
 
 
 
 
 
Serum creatinine 
 
X 
 
X 
 
X 
 
X 
 
X 
 
X 
CBC* 
 
X 
 
X 
 
X 
 
X 
 
X 
 
X 
Serious Adverse event report** 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
Pregnancy## 
 
X 
 
X 
 
X 
 
X 
 
X 
 
X 
Other Chemistries 
 
 
 
 
 
 
 
 
 
 
 
 
Relevant biological markers related to the 
pathogenesis of diabetes and its complications 
 
 
 
 
 
 
 
 
 
X 
 
 
Economic Evaluation 
 
 
 
 
 
 
 
 
 
 
 
 
Resource Utilization 
 
 
 
 
 
 
 
X 
 
 
 
 
QWB 
 
X 
X 
 
 
 
X 
 
 
 
X 
 
 
EOS = end of study 
# Pregnancy tests as needed for participants on metformin based on symptoms and menstrual history and measured locally. 
* Collected from participant of the metformin treatment group on study metformin measured locally.    
**   Serious Adverse events will be collected at Annual, Mid-year and Interim follow-up visits. 
*** Specimen for IA2 and GAD antibodies will be collected at the time of confirmation and will be analyzed for those who converted. 
+ For diabetic participants: HbA1c is collected at Mid-Year visits; the 30’ insulin and 30/120’ glucose collections are discontinued 
++ The following will be completed at study end: ABI, retinal photography, coronary artery calcium 
+++ DXA scans will be completed on a sample of participants during DPPOS Year 12 
 
 
 

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Outcomes Schedule, DPPOS Phase 3: Visit Years 13-18 
Participant DPPOS visit year 
Year 13 
Year 14 
Year 15 
Year 16 
Year 17 
Year 18 
Visit calendar year 7/1/14-10/31/15 
7/1/15-10/31/16 
7/1/16-10/31/17 
7/1/17-10/31/18 
7/1/18-10/31/19 
7/1/19-10/31/20 
DPPOS funding calendar year 
2/1/15-1/31/16 
2/1/16-1/31/17 
2/1/17-1/31/18 
2/1/18-1/31/19 
2/1/19-1/31/20 
2/1/20-1/31/21 
Mid-year or Annual visit 
Mid 
Ann 
Mid 
Ann 
Mid 
Ann 
Mid 
Ann 
Mid 
Ann 
Mid 
Ann 
Glycemia 
 
 
 
 
 
 
 
 
 
 
 
 
Fasting glucose 
 
X 
 
X 
 
X 
 
X 
 
X 
 
X 
120' glucose+ 
 
 
 
X 
 
 
 
X 
 
 
 
X 
HbA1c  
 
X 
 
X 
 
X 
 
X 
 
X 
 
X 
Insulin Secretion and Sensitivity 
 
 
 
 
 
 
 
 
 
 
 
 
Fasting insulin 
 
X 
 
X 
 
 
 
X 
 
 
 
X 
Lipids 
 
 
 
 
 
 
 
 
 
 
 
 
Lipid profile 
 
 
 
X 
 
 
 
X 
 
 
 
X 
Kidney Function 
 
 
 
 
 
 
 
 
 
 
 
 
Urine Albumin & Creatinine 
 
X 
 
X 
 
X 
 
X 
 
X 
 
X 
Serum Creatinine 
 
X 
 
X 
 
X 
 
X 
 
X 
 
X 
History 
 
 
 
 
 
 
 
 
 
 
 
 
Symptoms and Events (including CVD and Cancer) 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
Cancer Risk Factors 
 
X 
 
X 
 
X 
 
X 
 
X 
 
X 
Physical 
 
 
 
 
 
 
 
 
 
 
 
 
Weight 
 
X 
 
X 
 
X 
 
X 
 
X 
 
X 
Height 
 
 
 
 
 
X 
 
 
 
 
 
X 
Waist Circumference 
 
X 
 
X 
 
 
 
X 
 
 
 
 
DXA (bone and body composition measures)++ 
 
 
 
 
 
 
 
 
 
X 
 
 
Blood Pressure 
 
 
Arm BP 
 
X 
 
X 
 
X 
 
X 
 
X 
 
X 
Quality of Life 
 
 
Beck 
 
 
 
 
 
X 
 
 
 
 
 
 
SF-36 
 
 
 
 
 
X 
 
 
 
 
 
 
Urinary Incontinence 
 
 
 
 
 
X 
 
 
 
 
 
 

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Outcomes Schedule, DPPOS Phase 3: Visit Years 13-18, Continued 
Participant DPPOS visit year 
Year 13 
Year 14 
Year 15 
Year 16 
Year 17 
Year 18 
Visit calendar year 7/1/14-10/31/15 
7/1/15-10/31/16 
7/1/16-10/31/17 
7/1/17-10/31/18 
7/1/18-10/31/19 
7/1/19-10/31/20 
DPPOS funding calendar year 
2/1/15-1/31/16 
2/1/16-1/31/17 
2/1/17-1/31/18 
2/1/18-1/31/19 
2/1/19-1/31/20 
2/1/20-1/31/21 
Mid-year or Annual visit 
Mid 
Ann 
Mid 
Ann 
Mid 
Ann 
Mid 
Ann 
Mid 
Ann 
Mid 
Ann 
Physical Activity, Nutrition, Behavior, Functional 
 
 
 
 
 
 
 
 
 
 
 
 
ADL/IADL 
 
X 
 
 
 
X 
 
 
 
X 
 
 
Sexual Function 
 
 
 
 
 
X 
 
 
 
 
 
 
Physical Function including the 6-minute walk test 
 
 
 
 
 
X 
 
 
 
 
 
X 
Spirometry 
 
 
 
 
 
X 
 
 
 
 
 
X 
MAQ 
 
 
 
 
 
 
 
 
 
 
 
X 
Cognition 
 
 
 
 
 
 
 
 
 
 
 
 
Cognitive Function  
 
 
 
 
 
X 
 
 
 
 
X 
X 
Cardiovascular 
 
 
 
 
 
 
 
 
 
 
 
 
ECG 
 
 
 
X 
 
 
 
X 
 
 
 
 
Eye 
 
 
 
 
 
 
 
 
 
 
 
 
Retinal Photography and OCT 
 
 
 
 
 
 
 
X 
 
 
 
 
Neurologic 
 
 
 
 
 
 
 
 
 
 
 
 
Monofilament 
 
X 
 
X 
 
X 
 
X 
 
X 
 
X 
MNSI 
 
X 
 
 
 
 
 
 
 
 
 
MNSI questionnaire only  
 
 
 
 
 
 
 
 
X 
 
X 
Sensory exam (vibration and pinprick) 
 
 
 
 
 
 
 
 
 
X 
 
X 
Heart rate variability 
 
 
 
X 
 
 
 
X 
 
 
 
 
Saved Specimens 
 
 
 
 
 
 
 
 
 
 
 
 
Fasting Serum and EDTA Plasma 
 
X 
 
X 
 
X 
 
X 
 
X 
 
X 
Spot Urine 
 
X 
 
X 
 
X 
 
X 
 
X 
 
X 
Additional Safety Measures 
 
 
 
 
 
 
 
 
 
 
 
 
Serum Creatinine 
 
 
 
X 
 
 
 
X 
 
 
 
 
CBC* 
 
X 
 
 
 
 
 
 
 
 
 
 
Vitamin B12* 
 
 
 
X 
 
 
 
X 
 
 
 
 
Serious Adverse Event report** 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
Pregnancy# 
 
X 
 
X 
 
X 
 
X 
 
X 
 
X 

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Economic Evaluation 
 
 
 
 
 
 
 
 
 
 
 
 
Resource Utilization 
 
 
 
 
 
 
 
X 
 
 
 
X 
QWB 
 
 
 
 
 
 
 
X 
 
 
 
 
+ For diabetic participants: The OGTT with 120’ glucose collection is discontinued 
# Pregnancy tests as needed for participants on metformin based on symptoms and menstrual history and measured locally. 
* CBC and/or B12 for participants actively taking study metformin  
** Serious Adverse events will be collected at Annual, Mid-year and Interim follow-up visits. 
++ DXA scans will be completed on a sample of participants during DPPOS Year 17 

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12.1. Visit Schedule 
 
Annual visits will be targeted for the anniversary of the participant’s original DPP 
randomization date.  Mid-year visits will take place 6 months before and after annual visits.  

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77
13. 
STUDY TIMETABLE 
 
Diabetes Prevention Program 
 
Phase I 
July 1994 – June 1996 
Protocol Development and Implementation 
 
July 1994 – December 1995 
Protocol Development 
 
January 1996 – June 1996 
Protocol Implementation 
Phase II 
July 1996 – June 2002 
Participant Randomization and Follow-up 
 
July 1996 – June 1999 
Recruitment and Follow-up 
 
July 1999 – December 2001 
Participant Follow-up 
Phase III 
June 2001 
Initiate Study Close-out and Data Analysis 
Phase IV 
January 1, 2002 
Bridge Period Starts 
  
August 31, 2002 
Bridge Period Ends 
Diabetes Prevention Program Outcomes Study 
Planning 
January 2002 – August 31, 2002 
Protocol development 
Phase 1 
September 1, 2002 – January 31, 2009  Participant follow-up 
 
July 2006 – October, 2007 
Year 5 major visit 
 
February 1, 2008 – January 31, 2009 
Phase 1 Analysis 
 
June 2008 
Submit funding renewal 
Phase 2 
February 1, 2009 – October 2015 
Participant follow-up 
 
July 2012 – October 2013 
Year 11 major visit 
 
October 2013 
Begin Phase 2 Analysis 
 
May 2014 
Submit funding renewal 
 
March 2015 
Re-submit funding renewal 

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Phase 3 
February 1, 2015 – October 2020 
Participant follow-up 
 
February 1, 2015 – January 2016 
Bridge period funding awarded 
 
July 2017 – October 2018 
Year 16 major visit 
 
February 1, 2019 – January 31, 2021 
DPPOS Phase 3 (first 5 years) analysis 
 
May 2020 
Submit funding renewal 

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