vitamin d 25-hydroxy

Text-only Preview

Whatis vitam in 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 cana lso 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
consideredbiol ogically inactive until it undergoes two enzymatic hydroxylation reactions.
VitaminD 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-vitaminto 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(cal citriol), which is a major formo fvitamin D to be stored in human
body, it circulates bound to a specific plasma carrier protein, vitamin D binding protein, and the
half-lifeapproximately 15 daysat a concentrationof 25-200 nmol/L.