Vitamin D3 vs D2

D3 is cholecalciferol, the form skin makes from sunlight and the form in most supplements. D2 is ergocalciferol, made by irradiating yeast or mushrooms, and it is the vegan option and the one UK prescriptions historically used. The 2012 meta-analysis usually quoted for D3's advantage found exactly that overall, but its own subanalysis is the part that gets dropped: the difference held for bolus dosing and was lost with daily supplementation. So for years the claim outran the evidence for the way most people actually take it. A 2024 meta-analysis filled that in. Across twelve daily-dosed comparisons measured by mass spectrometry, the rise in total 25-hydroxyvitamin D was 10.39 nmol/L lower on D2 than on D3, about 40% less, with body mass index the strongest thing modifying the response. Both forms raise their own metabolite similarly; the gap is in the total, which is what a blood test reports.

Stack Almanac tracks which D form each product uses and totals your intake against the SACN reference of 10 micrograms a day, so a D2 prescription and a D3 capsule are not read as interchangeable numbers.