There are two forms of Vitamin D found in food and supplements: Vitamin D2, which is found in mushrooms, and Vitamin D3, which is found in animal foods. Vitamin D2 is not as bioavailable as D3, which means your body cannot use it as readily; however, it can still raise your vitamin D levels.[1] Most D3 supplements are derived from lanolin, a waxy substance secreted by the skin glands of wooly animals. Sheep are sheared, then the lanolin coating is squeezed off the wool. Since the sheep are not killed in the process, this source of D3 will be acceptable to some vegetarians. For vegans, the only acceptable D3 supplements will be the ones explicitly labeled as vegan, which derive their vitamin D3 from lichen extracts.