vitamin D

vitamin D, any of a group of fat-soluble vitamins important in calcium metabolism in animals. It is formed by ultraviolet radiation (sunlight) of sterols present in the skin. The term vitamin D refers to a family of compounds that are derived from cholesterol. There are two major forms of vitamin D: vitamin D₂, found in plants and better known as ergocalciferol (or calciferol), and vitamin D₃, found in animal tissues and often referred to as...