Vitamin D is one of the fat soluble vitamins; it plays an important role in maintaining the normal blood levels of calcium and phosphate which are needed for normal mineralization of bone, muscle contraction, nerve conduction and proper cellular function of the body, it also plays a role in the immune modulation and evidence suggest that it has an anti-cancer properties.
The skin plays an important role in the formation of vitamin D; vitamin D can also be obtained from certain food, and supplements. When we are exposed to sun, Ultraviolet B radiation (UVB) found in the sunlight will convert cholesterol (7-dehydrocholesterol) found in the skin to Vitamin D3 (Cholecalciferol), Vitamin D3 will be transported to the liver where it will be converted to Calcidiol (25 D3) and this is what is tested when we measure Vitamin D level in the blood, normal level is between 80 – 175 nmol/L. Calcidiol will be carried to the kidney and will be converted there to Calcitiol (1, 25 D3) which is the active form of vitamin D; it will be released to the circulation and will be carried in the plasma to the target organs. Vitamin D toxicity doesn’t usually occur if we are exposed for a long period of time to sunlight and this is because once Vitamin D3 concentration produced in the skin reaches equilibrium, further Vitamin D3 produced will be degraded by the same Ultraviolet light that created it.
Sources of Vitamin D: 1- The main source of Vitamin D comes from the exposure of our body to sunlight (see above). 2- Food sources: like oily fish such as salmon and sardines butter, egg yolks, some food can be fortified with Vitamin D like milk and cereals. 3- Vitamin D supplements.