The main difference between vitamin D2 and vitamin D3 is that D2 (ergocalciferol) is derived from plants, whereas D3 (cholecalciferol) has long been found only in animal sources like lanolin, an oil produced in sheep's wool (that is, until lichen-derived D3 became commercially available!). D2 is more commonly found in fortified foods and is cheaper to produce. D3 is the active form of vitamin D, meaning your body doesn't have to convert it. Research also shows that D3 is more effective at raising blood levels than D2.