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

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