Translations:Cholecalciferol/21/en

Mechanism of action

By itself cholecalciferol is inactive. It is converted to its active form by two hydroxylations: the first in the liver, by CYP2R1 or CYP27A1, to form 25-hydroxycholecalciferol (calcifediol, 25-OH vitamin D₃). The second hydroxylation occurs mainly in the kidney through the action of CYP27B1 to convert 25-OH vitamin D₃ into 1,25-dihydroxycholecalciferol (calcitriol, 1,25-(OH)₂vitamin D₃). All these metabolites are bound in blood to the vitamin D-binding protein. The action of calcitriol is mediated by the vitamin D receptor, a nuclear receptor which regulates the synthesis of hundreds of proteins and is present in virtually every cell in the body.