Vitamin D,Insulin Resistance,and Type 2 Diabetes

Vitamin D deficiency has become a major public health problem in the United States and worldwide due to its increasing prevalence and potential health risks. There is growing evidence from experimental studies that vitamin D is essential for pancreatic insulin secretion and peripheral insulin action through binding to the vitamin D receptor (VDR). Observational evidence, primarily from cross-sectional studies, has shown that low dietary vitamin D intake or vitamin D levels are inversely related to glucose intolerance, insulin resistance, decreased insulin secretion, as well as prevalence of the metabolic syndrome. Population genetic data for an association between VDR gene polymorphisms and type 2 diabetes have been sparse and yielded inconsistent results. Prospective data, although limited, tend to support an inverse association between serum 25(OH) vitamin D levels and incident type 2 diabetes. Direct evidence from randomized trials on the effect of vitamin D supplements on insulin homeostasis, however, remains limited. Future well-designed randomized clinical trials are warranted to address the potential beneficial effect of vitamin D supplementation on preventing type 2 diabetes.