What you dont know about vitamins

Vitamin D is also known as cholecalciferol. It is produced in the skin by UV radiation of 7- dehydrocholessterol. As long as the body is exposed to adequate sunlight, there is little or no dietary requirement for vitamin D.

The main role of vitamin D is the regulation of calcium metabolism. Vitamin D itself is biologically inactive, and it must be metabolized to its biologically active form. After it is consumed in the diet or synthesized in the epidermis of the skin, vitamin D enters the circulation and is transported to the liver. In the liver, vitamin D is hydroxylated to form 25- hydroxylvitamin D, also called 25- hydroxycholecalciferol or 25- (OH)D (calcidiol). 25- (OH)D is the major circulating form of vitamin D. in the kidneys, the 25 (OH)D-1-hydroxylase enzyme catalyses, a second hydroxylation of 25- (OH) D, resulting in the formation of 1,25 – dihydroxyvitamin D, also called 1, 25- dihydroxylation of 25 – (OH) 2D, or 125-DHCC (calcitriol). This is the most potent form of vitamin D in the body. Most of the physiological effects of vitamin D in the body are related to the activity of 1,25- DHCC. 1-25- (OH)2 D acts in the intestine to increase calcium absorption, where it induces synthesis of calbinden in the intestinal mucosal cells required for Ca2+ transport. In bone, 125 – (OH) 2D and parathormone (PTH) act synergistically to promote normal bone mineralization by stimulating osteoblast formation and activity. Finally, PTH and 1, 25 – (OH) 2D inhibit Ca2+ excretion in the kidneys by stimulating Ca2+ reabsorption in the distal renal tubules.