Vitamin D3 is also known as cholecalciferol. It is a steroid hormone produced in the skin when exposed to ultraviolet light (endogenous source) or taken in from dietary sources (exogenous). Its molecular formula is C27H44O. The active form of cholecalciferol or 1,25-dihydroxycholecalciferol has an important role in maintaining blood calcium and phosphorous levels and mineralization of bone. In the activated form, cholecalciferol binds to vitamin D receptors and modulates gene expression. This leads to an increase in serum calcium concentrations by increasing intestinal absorption of phosphorus and calcium, promoting distal renal tubular reabsorption of calcium and increasing osteoclastic resorption.
