Clinical trial NCT00784511: Vitamin D, Glucose Control and Insulin Sensitivity in African-Americans
Official title: Vitamin D, Glucose Control and Insulin Sensitivity in African-Americans
Study type: INTERVENTIONAL
Overall status: COMPLETED
Phase: PHASE2
Conditions: Type 2 Diabetes
Keywords: diabetes
vitamin D
African Americans
overweight
insulin sensitivity
glucose control
Lead sponsor: Tufts University
Sponsor class: OTHER
First posted: 2008-11-04
Enrollment: 100
Sex: ALL
Minimum age (years): 40
Standard ages: ADULT
OLDER_ADULT
Accepts healthy volunteers: yes
Allocation: RANDOMIZED
Intervention model: PARALLEL
Primary purpose: PREVENTION

Brief summary: North American blacks tend to have low blood levels of vitamin D because pigmentation blocks vitamin D production in the skin. They also have higher rates of developing type 2 diabetes and higher rates of complications from the disease compared with whites. Although there is compelling evidence that adequate vitamin D may reduce the risk for type 2 diabetes in whites, recent evidence from a national survey demonstrated an association of vitamin D with diabetes in whites but not in blacks. However, the central hypothesis of this study is that providing enough supplemental vitamin D to blacks (raising their blood levels higher than that of most participants in the survey) will improve blood measures related to diabetes risk. The proposed study is a 12-week randomized, double-blind, placebo-controlled experiment designed to examine the effect of vitamin D supplementation (100 μg/d ) on insulin secretion, insulin sensitivity and glucose control in pre-diabetic black men and women aged 40 and older.


Eligibility criteria: Inclusion Criteria:

* African-American by self designation
* Glucose intolerance defined as FPG ≥ 100 mg/dl or A1c ≥ 5.8%
* BMI 25.0-39.9
* Age 40 or older

Exclusion Criteria:

Medical Conditions

* Diabetes potentially requiring pharmacotherapy, defined as A1c \> 7%
* Uncontrolled thyroid disease
* Current parathyroid, liver or kidney disease
* Renal stone within 5 years
* Sarcoidosis, current pancreatitis, active tuberculosis, hemiplegia, gout
* Inflammatory bowel disease, colostomy, malabsorption
* Cancer other than basal cell skin cancer within 5 years
* Uncontrolled arrhythmia in past year
* Albinism or other condition associated with reduced skin pigmentation
* Pregnancy over the last 1 year
* Intent to become pregnant
* Menopause onset within 1 year
* Any other unstable medical condition Laboratory Tests
* Fasting plasma glucose \< 100
* Hemoglobin A1c \> 7%
* Laboratory evidence of liver disease (e.g. AST \> 70 U/L or ALT \> 72 IU/L)
* Laboratory evidence of kidney disease (e.g. estimated glomerular filtration rate \< 60 ml/min/1.73 m2).
* Elevated spot urine calcium to creatinine ratio \> 0.38 mg/dl\*
* Abnormal serum calcium (serum calcium \> 10.5 mg/dl)
* Anemia (Hematocrit \< 36% in men, \<33% in women) Medications (use in past three months)
* Estrogen or testosterone
* Prescription vitamin D
* Lithium
* Oral corticosteroids
* Anti-seizure medications
* Unstable doses of psychotropics or phenothiazines
* Cholestyramine Supplements (current use - may discontinue after screening)
* Vitamin D supplements, cod liver oil, calcium supplements Other
* Body mass index less \<25 or \> 39.9
* Consumption of more than 14 alcoholic drinks per week
* Inability to attend all three study visits as scheduled
* Inability to provide written informed consent
* age \< 40 years
* not African-American (by self-designation)
* Participation in another research intervention study

  * corresponds to a 24-hour urinary calcium excretion \> 400 mg

Primary outcomes:
measure: Insulin secretion rate
timeFrame: 12 weeks
measure: Insulin sensitivity index
timeFrame: 12 weeks
measure: 2-hr post load glucose
timeFrame: 12 weeks
Secondary outcomes:
Other outcomes:
Locations:
city: Boston
country: United States
facility: Jean Mayer USDA Human Nutrition Research Center on Aging at Tufts University
state: Massachusetts
Study officials:
References: