Vitamin D is a fat-soluble vitamin, which acts like a hormone, regulating the formation of bone and the absorption of calcium and phosphorus from the intestine. It helps to control the movement of calcium between bone and blood. The term vitamin D also refers to metabolites and other analogues of these substances. It plays an important role in the maintenance of organ systems. It regulates the calcium and phosphorus levels in the blood by promoting their absorption from food in the intestines, and by promoting re-absorption of calcium in the kidneys. It promotes bone formation and mineralization and is essential in the development of an intact and strong skeleton.