VITAMIN D

Vitamin D is a fat-soluble prohormone that can be obtained from foods—either the few foods in which it is naturally present, such as fish, egg, mushroom or fortified foods—as well as from dietary supplements. It is also produced endogenously when ultraviolet rays from the sun react with 7-dehydrocholesterol in the skin, converting it into the vitamin. Vitamin D has a variety of actions in the body. It binds to the vitamin D receptor (VDR), which then binds to the retinoid X receptor (RXR) and activates the expression of numerous genes. Through this mechanism, vitamin D promotes calcium absorption in the gut and helps maintain calcium and phosphate levels to promote healthy bones. It also helps regulate genes involved in cell growth, neuromuscular and immune function, and reduction of inflammation. Accordingly, vitamin D deficiency has been linked with a wide range of diseases.