US, but despite its use, the incidence of nutritional rickets is on the rise in the US and worldwide (Beck- Neilsen et al, 2009;Thatcher et al, 2013)( Havard school of Public health, Mittal et al , 2009)
Vitamin D has two major forms D2(ergocalciferol) and D3 (cholecalciferol). D2 is synthesized by plants and also is added to food while D3 is consumed in animal based food and also synthesized in the human skin via the action of sunlight (). D2 and D3 differ in their side chain structure but this difference does not affect their metabolism or their roles as prohormones.()
The production of vitamin D3 in the skin involves a series of reactions that starts with ...view middle of the document...
A small proportion of vitamin D remains in a free form in the circulation and has a serum t1/2 of about 5 hours till is cleared by the liver.
The second enzymatic reaction of vitamin D occurs in the kidney and 25OHD is hydroxylated by the 1α-hydroxylase enzyme to form calcitriol (1.25-Dihydroxyvitamin D). ( Mithal et al, 2009, BMJ) , Calcitriol (1,25-dihydroxyvitamin D) is the biologically active form of vitamin D. Calcitrol binds to vitamin d binding protein and is transported to target organs where it binds to vitamin D receptor (VDR). VDR’s are is located on nuclei as well as the cell membrane of target cells throughout the body. By binding to these VDR, vitamin D regulates gene expression at the transcriptional level (Jones et al., 1998; Jurutka et al., 2001). , Vitamin D Receptors are also found in the b and t lymphocytes, and its presence in these tissues has led researchers to imply that calcitrol may be involved in other roles such as cell proliferation and differentiation ().Calcitriol is degraded in part by being hydroxylated an enzyme 24-hydroxylase which is also in the kidney
Calcitrol and the parathyroid hormone (PTH) play an important role in the requlation of calcium level. Calcitrol influences calcium levels primary by controlling...