In adults with pre-diabetes (hemoglobin A1C values between 5.8 and 6.9 %) and baseline vitamin D levels less than 30 ng/mL, following a mean weekly dose of 88,865 IUs of vitamin D (n=56), there was no change in insulin secretion, insulin sensitivity, or diabetes incidence compared to placebo (n=53) after one year. This evidence concerns the gene INS and diabetes mellitus.