Vitamin D Supplementation Doesn't Prevent Type 2 Diabetes

Low vitamin D levels have been associated with excess risk for developing type 2 diabetes, but proof of a causal relation is lacking. In two previous randomized trials — Norwegian and Japanese studies with about 500 and 1200 participants, respectively — vitamin D supplementation did not prevent progression from prediabetes to diabetes (NEJM JW Gen Med Jun 1 2016 and Clin Endocrinol Metab 2016; 101:1647; Diabetes 2018; 67[Suppl 1]:LB34). Now, in the largest randomized trial to date, about 2400 U.S. adults with prediabetes received 4000 IU of vitamin D₃ or placebo daily. Participants were enrolled regardless of their vitamin D levels; at baseline, mean 25-hydroxyvitamin D (25[OH]D) level was 28 ng/mL, and 22% of patients had levels below 20 n…