Vitamin D is a fat-soluble vitamin as well as a hormone. It was first identified in the 1920s after a search to find the cause and cure for rickets. It is obtained through food sources as well as manufactured through the skin from sunlight. There are also three forms of vitamin D; vitamin D1 (calciferol), vitamin D2 (ergocalciferol), and vitamin D3 (cholecalciferol). These forms of vitamin D are converted in the liver and kidneys to the hormone calcitriol, which is the active form of vitamin D.
Vitamin D is a vitamin as well as a hormone.