Here's something I found that may be of interest if you're veg:
http://ods.od.nih.gov/factsheets/vitamind.aspsnip...
Dietary supplements
In supplements and fortified foods, vitamin D is available in two forms, D2 (ergocalciferol) and D3 (cholecalciferol). Vitamin D2 is manufactured by the UV irradiation of ergosterol in yeast, and
vitamin D3 is manufactured by the irradiation of 7-dehydrocholesterol from lanolin and the chemical conversion of cholesterol <10>. The two forms have traditionally been regarded as equivalent based on their ability to cure rickets, but evidence has been offered that they are metabolized differently. Vitamin D3 could be more than three times as effective as vitamin D2 in raising serum 25(OH)D concentrations and maintaining those levels for a longer time, and its metabolites have superior affinity for vitamin D-binding proteins in plasma <5,39,40>. Because metabolite receptor affinity is not a functional assessment, as the earlier results for the healing of rickets were, further research is needed on the comparative physiological effects of both forms. Many supplements are being reformulated to contain vitamin D3 instead of vitamin D2 <40>. Both forms (as well as vitamin D in foods and from cutaneous synthesis) effectively raise serum 25(OH)D levels <5>.