The role of Vitamin D in the prevention of type 2 diabetes: To d or not to d?

Abstract

Evidence on biological plausibility from mechanistic studies and highly consistent data from observational studies raise the possibility that optimizing Vitamin D status may reduce the risk of type 2 diabetes. However, the observational nature of cohort studies precludes a definitive assessment of cause and effect because residual confounding or reverse causation cannot be excluded. Confounding is especially problematic with studies of Vitamin D because blood 25-hydoxyVitamin D concentration is not only an excellent biomarker of Vitamin D status, reflecting intake or biosynthesis, but also an excellent marker of good overall health. Results from underpowered trials and post hoc analyses of trials designed for nondiabetic outcomes do not support a role of Vitamin D supplementation for prevention of type 2 diabetes among people with normal glucose tolerance. Whether Vitamin D supplementation may have a role in the prevention of diabetes in high-risk populations remains to be seen. Adequately powered, randomized trials in well-defined populations (e.g., prediabetes) are ongoing and expected to establish whether Vitamin D supplementation lowers risk of diabetes.