Mini-review. Vitamin D for the prevention of type 2 diabetes: Evidence and implications

Prediabetes is common worldwide and offers a critical opportunity for interventions to prevent type 2 diabetes. Vitamin D has biologically plausible effects on beta cell function, insulin sensitivity, and the immune system, and observational studies consistently associate higher 25-hydroxyvitamin D (25[OH]D) levels with a lower risk of diabetes. Three randomized, double-blind, placebo-controlled trials designed specifically for adults with prediabetes tested moderate-to-high doses of vitamin D 3 (Tromsø, D2d) or an active analog (DPVD). Each study showed a modest reduction in progression to type 2 diabetes. An individual participant data meta-analysis of these trials ( n = 4190) demonstrated a 15% relative risk reduction, with greater benefit among those with low baseline 25(OH)D levels and BMI