Vitamin D is a fat soluble nutrient. Vitamin D is found in Cod liver oil vitamin D-fortified foods egg yolks & butter. However the majority of vitamin D in the body is created during a chemical reaction that starts with sunlight exposure to the skin. Cholecalciferol (vitamin D3) is the animal form of this vitamin though our product is synthetic making it suitable for both vegans & vegetarians. What Does Vitamin D3 Do? Vitamin D contributes to the normal function of the immune system & healthy inflammatory response & maintenance of normal muscle function.