UVitamin D uyi-Vitamin futhi futhi uyi-hormone ye-steroid, ikakhulukazi kufaka phakathi i-VD2 ne-VD3, intambo yawo ifana kakhulu. UVitamin D3 no-D2 baguqulwa baba ngu-25 hydroxyl Vitamin D (kufaka phakathi i-25-Dihydroxyl Vitamin D3 ne-D2). 25- (oh) vd emzimbeni womuntu, ekwakheni okuzinzile, okuhlushwa okuphezulu. 25- (oh) vd ukhombisa inani eliphelele le-Vitamin D, kanye nekhono lokuguqulwa kwe-Vitamin D, ngakho-ke 25- (oh) vd kubhekwa njengenkomba engcono kakhulu yokuhlola izinga le-Vitamin D.Ikhithi yokuxilonga isuselwe ku I-Immunochrotography futhi inganikeza umphumela kungakapheli imizuzu eyi-15.