Vitamin D is a fat-soluble vitamin that is naturally present in very few foods. It is also produced endogenously when ultraviolet rays from sunlight strike the skin and trigger vitamin D synthesis. Vitamin D obtained from sun exposure, food, and supplements is biologically inert and must undergo two hydroxylations in the body for activation. These Hydroxylations occur in liver and kidney. Vitamin D promotes calcium absorption in the gut and maintains adequate serum calcium and phosphate concentrations to enable normal mineralization of bone and to prevent hypocalcemic tetany. It is also needed for bone growth and bone remodeling. It plays a major role in the cell growth, neuromuscular and immune function, inflammation and maintenance of normal bone mineral density (BMD).