Can Vitamin D Supplementation Prevent Type 2 Diabetes?

Animal experiments and observational studies in humans suggest that vitamin D deficiency might play a role in development of diabetes. To examine whether supplementation affects progression to diabetes, investigators in Norway randomized 511 adults with prediabetes (impaired fasting glucose or impaired glucose tolerance) to receive either vitamin D₃ (20,000 IU weekly) or placebo for 5 years. At baseline, mean serum 25-hydroxyvitamin D (25(OH)D) level was 24 ng/mL; during the study, levels doubled in the treatment group and remained unchanged in the placebo group.

At 5 years, the proportions of patients who developed type 2 diabetes were similar in the vitamin D and placebo groups (40% vs. 44%; P=0.45); annual rates of progression to diabetes…