Vitamin D

Vitamin D is a fat soluble vitamin that occurs in two forms: ergocalciferol (activated ergosterol, vitamin D2), found in irradiated yeast, and is used to fortify milk; and cholecalciferol (activated 7-dehydrocholesterol, vitamin D3), formed in human skin by exposure to sunlight (ultraviolet radiation) and found chiefly in fish liver oils and egg yolks.