Cholecalciferol

Cholecalciferol (Vitamin D3) is a secosteroid produced naturally in human skin upon exposure to ultraviolet B radiation or obtained from dietary sources. It is biologically inactive until it undergoes two sequential hydroxylations—first by CYP2R1 or CYP27A1 enzymes in the liver forming calcifediol [25(OH)D], then by CYP27B1 enzyme primarily in the kidney forming calcitriol [1,25(OH)₂D₃], which is hormonally active. Calcitriol binds to and activates the nuclear vitamin D receptor (VDR), modulating gene expression related to calcium absorption and bone health. Deficiency leads to rickets or osteomalcemia; excess can cause hypercalcemia[2][4][7].

Other names

Vitamin D3ColecalciferolCalciolActivated 7-dehydrocholesterolOleovitamin D3Vitamin D-3

Cholecalciferol is biologically inactive and must be converted in the body to its active forms. It undergoes two hydroxylation steps—first in the liver to 25-hydroxycholecalciferol (calcifediol), then in the kidney to 1,25-dihydroxycholecalciferol (calcitriol). Calcitriol acts as a ligand for the vitamin D receptor (VDR), which regulates gene transcription involved in calcium and phosphate metabolism[1][2][7].