Insulin resistance and its impaired secretion are the core components of type 2 diabetes mellitus. Recently role of vitamin D has been highlighted in the pathogenesis of this disease. Vitamin D has been shown to maintain healthy glucose metabolism by increasing intracellular calcium levels and insulin secretion, by increasing GLUT4 activity and by suppressing the inflammatory response of various cytokines thereby protect the beta cells from oxidative injury. Low vitamin D levels were strongly associated with increased risk of type2 diabetes. Few studies have advocated maintaining vitamin D levels more than 30ng/ml to lower down the risk of this disease. But still more studies are required to establish this cut-off value. The results of vitamin D supplementation trials in preventing type2 diabetes are rather conflicting but it has been shown to be useful in improving impaired glucose tolerance in a pre-diabetic state. Vitamin D mediates its effect by interacting with vitamin D receptors (VDR) which are present in almost every tissue including beta cells in humans which also contains 1αhydroxylase enzyme. Gene polymorphism in VDR gene, Calbindin D-28K(carrier of vitamin D molecule in plasma) and 1α hydroxylase gene were positively linked to type2 diabetes but not in all population studies. In conclusion, deficient vitamin D levels increases the risk of developing type2 diabetes. However, more studies are required to ascertain the role of gene polymorphism and effect of vitamin D supplementation in type2 diabetes mellitus.
