Vitamin D (VD) is unique among the vitamins in the fact that it can either be synthesized in the skin from exposure to sunlight or taken from the diet. Apart from its role in calcium and bone homeostasis, VD and its metabolites are now known to have important roles in various other functions of human health, of which many still await to be discovered. Vitamin D deficiency (VDD) is now known to be rampant globally including the Indian sub-continent. In this review, the classical and

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... functions of VD are described. Further, we have discussed the prevalence of VDD in general, and in disease conditions, particularly in the Indian population. Studies carried out in pregnant women, cardiovascular disease patients, rheumatoid arthritis patients, both type 1 and type 2 diabetic subjects; all show VD deficient or insufficient status. Genetic and epigenetic variants in the genes involved in the VD metabolism play a fundamental role in individual differences in the VD status. Considering the plethora of VD functions, the recommended dietary allowance (RDA) of VD may need to be revised. Further, randomized control trials across India, and food fortification with VD to combat the VDD epidemic are needed.