Calcifediol (INN), also known as calcidiol, 25-hydroxycholecalciferol, or 25-hydroxyvitamin D (abbreviated 25(OH)D), is a prehormone that is produced in the liver by hydroxylation of vitamin D3 (cholecalciferol) by the enzyme cholecalciferol 25-hydroxylase which was isolated by Michael F. Holick. Physicians worldwide measure this metabolite to determine a patient's vitamin D status. At a typical daily intake of vitamin D3, its full conversion to calcifediol takes approximately 7 days.
Calcifediol is then converted in the kidneys (by the enzyme 25(OH)D-1α-hydroxylase) into calcitriol (1,25-(OH)2D3), a secosteroid hormone that is the active form of vitamin D. It can also be converted into 24-hydroxycalcidiol in the kidneys via 24-hydroxylation.

Chemical Name	calcidiol
Synonyms	Calcifediol,(εR,1R,3aS,4E,7aR)-4-[(2Z)-2-[(5S)-5-hydroxy-2-methylenecyclohexylidene]ethylidene]octahydro-α,α,ε,7a-tetramethyl-1H-indene-1-pentanol;25-Hydroxyvitamin D3;Calcifediol;25-Hydroxycholecalciferol;Calcidiol,Didrogyl,Hidroferol;Vitamin D3 25 Calcifediol;Collapse
CAS No.	19356-17-3
Molecular Formula	C27H44O2
Molecular Weight	400.63700
PSA	40.46000
LogP	6.73390

MDL number	MFCD00867077
EINECS number	242-990-9
PubChem number	24895612

Density	1.01 g/cm3
Boiling Point	529.2ºC at 760 mmHg
Flash Point	221.4ºC
Storage Condition	-20ºC

Safety Statements	28-36/37-45
WGK Germany	3
RIDADR	UN 2811 6
Risk Statements	R28
Hazard Codes	T+
Hazard Declaration	H225; H319
Symbol	GHS02, GHS07
Signal Word	Danger
Caution Statement	P210; P280; P305 + P351 + P338; P337 + P313; P403 + P235