Functions of Vitamin D

Vitamin D is a fat-soluble vitamin that can be found in food but significant amounts of vitamin D can also be produced by the body. It can be obtained from sun exposure, food, and supplements are biologically inert and must undergo two hydroxylations in the body for activation. The two major forms of which are vitamins D2 (ergocalciferol) and vitamin D3 (cholecalciferol). This paper not only looks into the essential function of vitamin D on the subject of bone health, but also other non-calcemic functions of vitamin D.
The major biologic function of Vitamin D is to maintain a healthy level of calcium and phosphorus. Vitamin D assures calcium and phosphorus that are vital for bone health, is always available to the body’s tissue. In fact, studies show that vitamin D increases the efficiency of the body’s absorption of calcium thirty to forty percent and phosphorus by eight percent. (Gilchrest). Without vitamin D, bones can become thin, brittle, soft, or misshapen. Calcitriol (active form of vitamin D) and parathyroid hormone (PTH) control the level of calcium in three ways (Brown, Philpott, Kalita). Firstly, vitamin D increases calcium absorption in the small intestine by up-regulating several genes that code for proteins required for the transport of dietary calcium into the enterocytes. Secondly, they stimulate bone breakdown by osteoclasts and thirdly, they reduce the excretion of calcium into the urine so that more calcium would remain in the blood. If the plasma becomes less than saturated with respect to calcium and phosphate, then mineralization fails, which results in rickets among children and osteomalacia among adults (DeLuca). Meanwhile, vitamin D and calcium are critical in preventing osteoporosis in men and women fifty years old and older.
Recently, a lot of scientific evidence points that vitamin D has functions beyond calcium homeostasis. One of the most recognized functions is cell differentiation by stimulating immature cells to become mature,