The 25-hydroxy metabolite of cholecalciferol — bypasses the hepatic CYP2R1 hydroxylation step, so it raises serum 25(OH)D faster and more predictably than D3 (Tmax ~4 h vs ~12 h; ~3× steeper 25(OH)D response slope). Water-soluble after hydroxylation, so does not partition into adipose — useful in obesity and malabsorption where D3 has attenuated response. Still requires renal CYP27B1 to reach 1,25(OH)₂D.
Half-Life (t½)
PO: 360h
Dosing Guidelines
PO: Typical 33.3 mcg (Range: 25–50 mcg)
Target Organ Systems
digestive
renal
Interactions
Vitamin D3 (synergistic): Same pathway — calcifediol is the hepatic metabolite of D3. Generally pick one unless rapid 25(OH)D correction is needed.
Magnesium (synergistic): Required cofactor for downstream 1α-hydroxylation and VDR activation.