Vitamin D and Type 2 Diabetes Study

The goal of the Vitamin D and type 2 diabetes (D2d) study is to determine if vitamin D supplementation works to delay the onset of type 2 diabetes in people at risk for the disease and to gain a better understand how vitamin D affects glucose (sugar) metabolism. Researchers at US sites will enroll people with pre-diabetes (people who have higher than normal blood glucose level but not high enough to meet the diagnosis of diabetes). The study will enroll participants over approximately 2 years and participants will be followed for approximately 3 years. Participants will receive either Vitamin D or a placebo by chance. Participants will take 1 pill a day for the duration of the study.