<prompt> What is the naturally occurring form of vitamin D in the human skin?Calciferol7 hydroeholesterol25 hydroxy cholecalciferol1,25 dihydroxy cholecalciferol  <response>: Calciferol is a fat-soluble, crystalline unsaturated alcohol produced by ultraviolet irradiation of ergosterol in plants. It is used as a dietary supplement in the prophylaxis and treatment of rickets, osteomalacia, and other hypocalcemic disorders. Also called ergocalciferol, ole vitamin D2, vitamin D2. See also rickets, viosterol.Ref: Ganong;s review of medical physiology; 24th edition; page no:-377 