Economic Evaluation of Combined Diet and Physical Activity Promotion Programs to Prevent Type 2 Diabetes Among Persons at Increased Risk: A Systematic Review for the Community Preventive Services Task Force

Diabetes is a highly prevalent, severe, and costly disease in the United States. Approximately 29 million Americans (9.3% of the U.S. population) had diabetes in 2012, and that number is projected to increase (1, 2). Diabetes is the leading cause of kidney failure, blindness, and amputation, as well as a major cause of heart disease and stroke (2). In the United States in 2012, the total medical cost of diagnosed diabetes was estimated at $176 billion, and the cost of productivity loss due to diabetes was another $69 billion (3). Type 2 diabetes accounts for 90% to 95% of all cases of diagnosed diabetes. Common risk factors for type 2 diabetes include obesity, family history of diabetes, physical inactivity, hypertension, hypercholesterolemia, and elevated glucose level. In addition, approximately 37% of the U.S. population aged 20 years or older and 51% of those aged 65 years or older had prediabetes in 2012, meaning that they were at increased risk for type 2 diabetes (2). However, only about 10% of at-risk persons knew their risk status (4). Randomized clinical trials around the world have shown that combined diet and physical activity promotion programs could prevent or delay progression to type 2 diabetes among persons at increased risk (58). Studies have also demonstrated the feasibility and effectiveness of such programs when they are implemented in primary care or community settings (9). In 2014, a systematic review done for the Community Preventive Services Task Force found that programs implemented in health care or community settings effectively reduced the risk for diabetes in persons at increased risk; increased the likelihood of reversion to normoglycemia; and reduced weight and other risk factors for cardiovascular disease, such as elevated blood pressure and lipid levels (10). Given the potentially large population that is eligible for diet and physical activity promotion programs and the resources needed for implementation, information on program cost and cost-effectiveness is critical for policy decisions, such as benefit coverage for payers, as well as planning for program design and implementation. As a companion to the aforementioned effectiveness review, we did this systematic economic review for the Community Preventive Services Task Force to estimate the cost associated with diet and physical activity promotion programs and the cost-effectiveness and costbenefit ratios of these programs. Methods Data Sources and Searches We searched the Cochrane Library, EMBASE, MEDLINE, PsycINFO, Sociological Abstracts, Web of Science, EconLit, and CINAHL for English-language articles published between January 1985 and 7 April 2015. Details of the search strategy are available on the Guide to Community Preventive Services (Community Guide) Web site (www.thecommunityguide.org) and in Appendix Table 1 (11). We also screened reference lists of relevant studies and reviews and considered studies identified by the parallel review of the effectiveness of diet and physical activity promotion programs (10). Appendix Table 1. Search Strategy: Combined Diet and Physical Activity Promotion Programs Among Persons at Increased RiskEconomic Review* Study Selection We included studies that provided information on program cost; costbenefit ratio; or incremental cost-effectiveness ratio (ICER), which is measured as dollars per life-year gained (LYG), quality-adjusted life-year (QALY) saved, or disability-adjusted life-year (DALY) averted. Included studies on program cost had to evaluate the actual program implementation cost. Included cost-effectiveness or costbenefit studies had to meet published criteria for conducting and reporting economic evaluation analysis (12). We used the same inclusion criteria as the aforementioned effectiveness review for study population, intervention, comparison population, and publication language (10). Criteria included a population at increased risk for type 2 diabetes, based on glycemic measures or risk scores for diabetes, presence of cardiovascular disease, or presence of the metabolic syndrome; intervention with both diet and physical activity components delivered in at least 2 contact sessions over at least 3 months; comparison with a similar population receiving either usual care (standard lifestyle advice) or no intervention for the cost-effectiveness studies; and publication in English. We further restricted our review to studies in high-income countries to provide economic estimates relevant to U.S. settings and populations. Data Extraction and Quality Assessment Two authors extracted data from each article according to the Cochrane systematic review protocol (13) and the Community Guide protocol for economic evaluations (14). Data Synthesis and Analysis Intervention costs are reported as program costs per participant, including costs to identify eligible participants (through recruitment in the community, referral from providers, or screening and referral in study settings) and to implement the diet and physical activity promotion program (staff time, training materials, and other costs). We also generated program costs per participant per session, calculated by dividing program costs per participant by the total number of core and maintenance sessions delivered. Medians and interquartile intervals (IQIs) of study estimates were reported as summary measures. If there were 4 data points, we reported the range; if there were 3 or fewer data points, all were reported. Subgroup analyses of intervention costs were done to explore potential factors affecting costs. For delivery setting, we grouped each study into those based on the U.S. DPP (Diabetes Prevention Program) study, in which the intervention was delivered in a clinical trial setting following rigorous procedures as described in study protocols (5), and those done in real-world settings, in which diet and physical activity promotion programs were translated to community or primary care settings, with (translational DPP programs) or without (translational non-DPP programs) explicit adaptation of DPP training materials. For delivery method, we categorized each study into 1 of the following groups: individual-based programs, in which a participant met 1-on-1 with the program provider at each core session; group-based programs, in which the participants met as a group with the program provider at each core session; or mixed programs, in which the core sessions included both individual and group sessions. For the type of personnel delivering the program, we grouped each study by whether the program was delivered by health professionals (such as medical staff, physicians, nurses, physiotherapists, case managers, or dietitians), trained laypersons (such as certified diabetes educators, lay health educators, trained community health workers, or trained volunteers with type 2 diabetes), or a mix of health professionals and trained laypersons. Cost-effectiveness estimates were measured as ICERs, with medians and IQIs provided as summary measures. To improve comparability of ICERs across the studies, we reported them separately by the outcome measures used in different studies: QALYs saved, LYGs, or DALYs averted. For studies found to be cost-saving, we calculated the negative net cost per QALY saved, LYG, or DALY averted whenever possible to calculate the median ICER. Two economic perspectives were considered: the health system perspective, in which only medical costs and benefits relevant to health systems were considered, and the societal perspective, in which direct nonmedical and indirect costs were also considered. When studies provided sufficient data, we calculated ICERs for perspectives beyond those reported. As with cost estimates, subgroup analysis of ICERs was done by delivery method. We examined cost-effectiveness estimates by type of analysis: within-trial analysis, in which ICERs were calculated from data on actual costs and benefits; modeling of a trial or extension of trials, in which studies used simulation models to estimate program cost and effectiveness during or beyond the trial period; or modeling of the national effect, in which studies estimated ICERs for programs delivered by scaling up programs to the entire country in which the study was conducted. Because time horizon is important in program planning and budget allocation, we reported ICERs by length of follow-up (short-term [<10 years] or long-term [10 years]). In addition, we reported ICERs stratified by country setting (U.S.- or nonU.S.-based) to better inform programs in the United States. All costs were adjusted to 2013 U.S. dollars by using the Consumer Price Index for medical care services (15) and annual foreign exchange rates from the Federal Reserve Bank for conversion of other currencies (16). If a study did not mention the year used in cost calculations, we assumed costs to be as of 1 year before the study publication year. Interventions were considered cost-effective if the ICER was less than $50000 per QALY saved, less than $50000 per LYG (17), or less than the per capita gross domestic product of the relevant country for cost per DALY averted, as recommended by the World Health Organization (18). Role of the Funding Source This study was done by employees of the U.S. government as part of their official duties and received no external funding. Results After screening, 28 studies met our inclusion criteria and were included in our final review (Figure 1) (1946). Of these, 6 cost-only studies (2023, 26, 27) and 6 cost-effectiveness studies (19, 24, 25, 2830) provided information on the actual cost of diet and physical activity promotion programs, and 22 contributed cost-effectiveness estimates of the programs (19, 24, 25, 2846). Fourteen studies were U.S.-based (1924, 26, 27, 31, 3538, 46). No costbenefit studies were identified. Figure 1. Summary of evidence search and selection. * Studies had abstracts only, were irrelevant, or did not me