vitamin d vitamin d vitamin d is a group of fat-soluble secosteroids responsible for increasing intestinal absorption of calcium, magnesium, and phosphate, and many other biological effects. in humans, the most important compounds in this group are vitamin d3 (cholecalciferol) and vitamin d2 (ergocalciferol). this article is about the family of d-"vitamins". for individual forms, see ergocalciferol, cholecalciferol, vitamin d4, vitamin d5, and calcitriol. vitamin ddrug classcholecalciferol (d3)class identifierssynonymscalciferolsuserickets, osteoporosis, vitamin d deficiencyatc codea11ccbiological targetvitamin d receptorclinical datadrugs.commedfacts natural products