Type 2 Diabetes
Conditions
Keywords
diabetes, vitamin D, African Americans, overweight, insulin sensitivity, glucose control
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.
Interventions
DIETARY_SUPPLEMENTcholecalciferol
4000 IU/d
OTHERmicrocrystalline cellulose
1/d
Sponsors
Tufts University
Study design
Allocation
RANDOMIZED
Intervention model
PARALLEL
Primary purpose
PREVENTION
Masking
QUADRUPLE (Subject, Caregiver, Investigator, Outcomes Assessor)
Eligibility
Sex/Gender
ALL
Age
40 Years to No maximum
Healthy volunteers
Yes
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
Design outcomes
Primary
| Measure | Time frame |
|---|---|
| Insulin secretion rate | 12 weeks |
| Insulin sensitivity index | 12 weeks |
| 2-hr post load glucose | 12 weeks |
Countries
United States
Outcome results
None listed