Vitamin D, Glucose Control and Insulin Sensitivity in African-Americans

Study Overview
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Brief Summary
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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.

Official Title
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Vitamin D, Glucose Control and Insulin Sensitivity in African-Americans

Conditions
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Type 2 Diabetes

Intervention / Treatment
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* Dietary Supplement: cholecalciferol
* Other: microcrystalline cellulose


Participation Criteria
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Eligibility Criteria
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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

Ages Eligible for Study
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Minimum Age: 40 Years

Sexes Eligible for Study
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All

Accepts Healthy Volunteers
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Accepts Healthy Volunteers

Study Plan
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How is the study designed?
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Design Details

Primary Purpose: Prevention
Allocation: Randomized
Intervention Model: Parallel Assignment
Masking: Quadruple


Arms and Interventions

| Participant Group/Arm | Intervention/Treatment |
| --- | --- |
| Experimental: 1 vitamin D3<br>vitamin D3, 4000 IU/d | Dietary Supplement: cholecalciferol<br>* 4000 IU/d<br>* Other names: vitamin D;|
| Placebo Comparator: 2<br>placebo | Other: microcrystalline cellulose<br>* 1/d<br>* Other names: placebo;|

What is the study measuring?
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Primary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Insulin secretion rate |  | 12 weeks | 
| Insulin sensitivity index |  | 12 weeks | 
| 2-hr post load glucose |  | 12 weeks | 

 Terms related to the study
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Keywords Provided by Centre Hospitalier Valida
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diabetes, vitamin D, African Americans, overweight, insulin sensitivity, glucose control