Vitamin D supplementation in minority subjects with both pre-diabetes and low vitamin D levels will delay the development of diabetes.

Low vitamin D levels 1) are associated with abnormalities in insulin secretion and insulin action, 2) predict the development of diabetes in those without diabetes, and 3) are more common in people with diabetes. Minority populations (African-Americans and Latinos) are more likely to have both low levels of vitamin D and diabetes. This study will identify minority individuals who are at increased risk for diabetes (those with central obesity, family history of diabetes in first degree relatives and either with hypertension or being treated for hypertension), and determine if they have both pre-diabetes, ie, impaired fasting glucose and/or impaired glucose tolerance, and low levels of vitamin D. Those that have both will be randomized to either high doses of vitamin D or placebo and insulin secretion and action as well as changes in the oral glucose tolerance test (reversion to normal, maintenance of pre-diabetes or development of diabetes) will be monitored at 3 month intervals for one year. This study will test the hypothesis that the increased amount of diabetes in minority populations may be due in part to low levels of vitamin D and whether supplementing this vitamin may delay the development of diabetes.

Inclusion Criteria:

1. Age greater than 40.
2. Impaired fasting glucose (FPG level greater than 100 and less than 126 mg/dl); and/or
3. Impaired glucose tolerance (2-h plasma glucose concentration after 75 gram glucose load greater than 140 and less than 200 mg/dl)
4. Serum 25-OHD less than 30 ng/ml
5. Able and willing to provide informed consent

Exclusion Criteria:

1. FPG greater than 126 mg/dl or 2-hour-OGTT plasma glucose greater than 200 mg/dl
2. Major psychiatric disorder on medication (excluding successfully treated depression)
3. Diagnosed diabetes mellitus
4. HIV/AIDS
5. Major hematological, hepatic (AST/ALT levels greater than or equal to 2 times normal) or renal eGFR less than 60 ml/min) disorder
6. History of carcinoma, except skin basal cell or squamous cell skin carcinomas
7. Heart failure, unstable angina or history of a myocardial infarction
8. Alcohol or substance abuse
9. Current treatment with glucocorticoids
10. Current treatment with diabetes medications, including metformin
11. Cushing's syndrome
12. Primary hyperparathyroidism
13. Nephrolithiasis
14. Pregnancy or breast-feeding
15. Regular visits to a tanning salon (unlikely in this minority population)