 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. 