Translations:Calcifediol/3/en

Biology

Calcifediol is the precursor for calcitriol, the active form of vitamin D. It is synthesized in the liver, by hydroxylation of cholecalciferol (vitamin D₃) at the 25-position. This enzymatic 25-hydroxylase reaction is mostly due to the actions of CYP2R1, present in microsomes, although other enzymes such as mitochondrial CYP27A1 can contribute. Variations in the expression and activity of CYP2R1, such as low levels in obesity, affect circulating calcifediol. Similarly, vitamin D₂, ergocalciferol, can also be 25-hydroxylated to form 25-hydroxyergocalciferol, (ercalcidiol, 25(OH)D₂); both forms are measured together in blood as 25(OH)D.