25 hydroxyvitamin d

1. What is vitamin D? Vitamin D refers to a group of fat-soluble secosteroids responsible for increasing intestinal absorption of calcium, iron, magnesium, phosphate, and zinc. There are approximately 30 molecules in the Vitamin D group, but the two most significant forms are vitamin D2 and vitamin D3, vitamin D2 also named ergocalciferol, which is synthesized by plants and is not produced by the human body, it has a purely dietary source, predominantly from yeasts, vitamin D3 also named cholecalciferol, which is made in large quantities in the skin when sunlight strikes bare skin, It can also be ingested from diet like oily fish, egg yolks, and fortified foods. Resurrection of vitamin D deficiency and rickets. Vitamin D, in either the D2 or D3 form, is considered biologically inactive until it undergoes two enzymatic hydroxylation reactions. Vitamin D metabolism During exposure to sunlight, 7-dehydrocholesterol in the skin absorbs solar UVB radiation and is converted into Pre-Vitamin D3 (pre-D3). DHCR7 encodes the enzyme 7-dehydrocholesterol reductase, which converts 7-dehydrocholesterol to cholesterol, thereby removing a precursor of 25-hydroxyvitamin D3 from the synthetic pathway of vitamin D3. Heat causes isomerization of pre-vitamin to vitamin D in the skin. Then vitamin D bound to plasma transport protein (D binding protein, also known as Gc protein) transport through blood to liver, and is hydroxylated in the liver at position 25 to form 25-hydroxyvitamin D (calcidiol) by the microsomal enzyme vitamin D 25-hydroxylase, which is encoded by the CYP2R1 and CYP27A1 genes in the liver. The 25 hydroxyvitamin D is the precursor of 1,25 hydroxyvitamin D 3 (calcitriol), which is a major form of vitamin D to be stored in human body, it circulates bound to a specific plasma carrier protein, vitamin D binding protein, and the half-life approximately 15 days at a concentration of 25-200 nmol/L. http://www.creative-diagnostics.com/news-vitamin-d-metabolism-and-25-hydroxyvitamin-d-38.h tm