The vegan form of vitamin D, which is called ergocalciferol or vitamin D2, has been shown to be as effective in raising blood levels of this nutrient as animal-derived vitamin D3 when it???s taken at a usual daily dose (1) (The RDA is 600 IUs; some experts recommend 1,000.) At megadoses, however, vitamin D2 may need to be taken more often.(2) But no one should be megadosing on vitamin D unless the