Vitamin D appears today as a vitamin with a multiple potentials. It’s involved in many physiological processes. It was for a long time confined for its role in phosphocalcic metabolism. Due to its dual food and endogenous origin, vitamin D constitutes a contributions and needs remain difficult to define and are currently under debate. On the other hand, the metabolism of this vitamin D is better known. Its metabolism involves a first hepatic hydroxylation leading to the formation of 25- hydroxyvitamin D 25OHD as well as a renal hydroxylation resulting in the formation of 1,25(OH)2 D, the active metabolite of the vitamin D. Vitamin D deficiency is defined by a serum 25OHD concentration below 20 ng/mL. On the other hand, the insufficiency in vitamin D is defined by a concentration between 20 and 30 ng/mL. The deficiency and insufficiency are very frequent situations associated with an increased risk of developing various pathologies. The effects of vitamin D supplementation on reducing the risk of fractures and falls are documented by various intervention studies. The other potential extra osseous effects of vitamin D are mainly documented by observational and experimental studies. Although there is not yet a consensus on the need for vitamin D. All experts agree that the recommended dietary allowance is very insufficient and should be increased.

Keywords : Vitamin D, Effects, Metabolism, Source.