Derived from UV-irradiated fungal ergosterol. Differs from D3 by an extra C22 double bond and C24 methyl, which reduces affinity for vitamin-D binding protein (DBP) and shortens the t½ of its 25-hydroxy metabolite. Same downstream activation — hepatic CYP2R1 → 25(OH)D2, renal CYP27B1 → 1,25(OH)₂D2 (ercalcitriol) — and same VDR binding. Head-to-head human RCTs show D2 raises serum 25(OH)D roughly 60–70% as efficiently as equimolar D3.
Half-Life (t½)
PO: 240h
Target Organ Systems
endocrine
digestive
renal
integumentary
Interactions
Vitamin D3 (synergistic): Same pathway; D3 is more efficient per IU at raising 25(OH)D. Generally pick one.
Magnesium (synergistic): Required cofactor for 25- and 1α-hydroxylation of both D2 and D3.