The Role of Vitamin D in Type 2 Diabetes and Hypertension

Increasing evidence from animal and human studies point to an important role of vitamin D in modifying risk of type 2 diabetes. Vitamin D has both direct (through activation of the vitamin D receptor) and indirect (via regulation of calcium homeostasis) effects on various mechanisms related to the pathophysiology of type 2 diabetes, including pancreatic beta-cell dysfunction, impaired insulin action, and systemic inflammation. Longitudinal observational studies report highly consistent results showing inverse associations between measured blood 25(OH)D concentration and risk of developing type 2 diabetes. The results from mostly underpowered trials and post hoc analyses of large trials that used small doses of vitamin D do not support a role of vitamin D for treatment of established type 2 diabetes or prevention of diabetes among those with normal glucose tolerance; however, in people with prediabetes, vitamin D reduces risk of progression from prediabetes to diabetes and promotes regression to normal glucose regulation. For optimal risk reduction, blood 25(OH) levels higher than those recommended by the National Academy of Medicine are needed.