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nightsurfer on 2009-09-03Vitamin D2 is much less effective than vitamin D3 in humans.
Armas LA, Hollis BW, Heaney RP.
J Clin Endocrinol Metab. 2004 Nov;89(11):5387-91.
Vitamin D2 potency is less than one third that of vitamin D3. Physicians resorting to use of vitamin D2 should be aware of its markedly lower potency and shorter duration of action relative to vitamin D3.