Amavithamini, ngezinye izikhathi ahunyushwa ngokuthi amavithamini, yigama elithile lokudla okunempilo. Zibhekisela ochungechungeni lwezinhlanganisela eziphilayo futhi ziyisigaba sokulandelela izinto eziphilayo ezidingekayo ukuze abantu nezilwane zigcine imisebenzi evamile yomzimba. Iningi alikwazi ukukhiqizwa umzimba ngokwawo futhi kufanele litholakale ekudleni. Ambalwa kuphela angahlanganiswa emzimbeni noma akhiqizwe ama-microorganisms amathumbu. Adlala indima ebalulekile ekukhuleni komuntu, ekusetshenzisweni komzimba, nasekuthuthukeni futhi angesinye sezakhi eziyisithupha ezinkulu (ama-carbohydrate, amafutha, amaprotheni, amaminerali, amavithamini, namanzi). Amavithamini awabambi iqhaza ekwakhiweni kwamangqamuzana omuntu noma anikeze amandla omzimba, kodwa abamba iqhaza ekuphenduleni kwamakhemikhali e-biochemical emzimbeni futhi alawule imisebenzi ye-metabolic yomzimba. Uma ukungena kwamavithamini kunganele, kuzoholela ekungalinganisweni kwe-metabolism yomuntu, okuholela ekunciphiseni ukuzivikela komzimba futhi kubangele "ukuntuleka kwamavithamini." Ukuntuleka kwamavithamini okuyinhloko kungabangelwa ukungadli ngokwanele ngenxa yokuntuleka kwamavithamini ekudleni noma ukunciphisa ukudla.
Ukuntuleka kwevithamini okwesibili kungabangelwa ukuncipha kwekhono lomzimba lokumunca amavithamini, isidingo esikhulayo samavithamini, noma ukuphazamiseka kweminye imithi. Amavithamini awumndeni omkhulu, onamashumi aziwayo okwamanje. Angahlukaniswa abe izigaba ezimbili eziyinhloko: amafutha-ancibilikayo namanzi{3}}ancibilikayo. Amanzi-amavithamini ancibilikayo ancibilika kalula emanzini kodwa hhayi-ezincibilikisini ezingezona ze-polar. Ngemuva kokumuncwa, kuncane kakhulu kugcinwa emzimbeni, kuthi umchamo ukhishwe ngokweqile. Amafutha-amavithamini ancibilikayo ancibilika kalula{10}kuzinto ezincibilikayo ezingezona ezipholile kodwa hhayi emanzini. Angakwazi ukumuncwa umzimba kanye namafutha futhi anqwabelene emzimbeni, ngezinga eliphansi lokuphuma. Ivithamini ngayinye ivame ukubhekana nokusabela okuningi, ngakho-ke amavithamini amaningi anemisebenzi eminingi. Amavithamini A, D, E, kanye no-K angamafutha-amavithamini ancibilikayo, kuyilapho amavithamini B no-C engamavithamini{15}}ancibilikayo emanzini. Ezinye izinto zifana namakhemikhali namavithamini athile futhi zingaguqulwa zibe amavithamini ngokusabela okulula kwe-metabolic. Lezi zinto zibizwa ngokuthi ama-provitamins. Isibonelo, -i-carotene ingaguqulwa ibe uvithamini A; I-7-dehydrocholesterol ingaguqulwa ibe uvithamini D3, kodwa lokhu kudinga ukusabela okuyinkimbinkimbi kwe-metabolic. I-Tryptophan, ingxenye ye-nicotinic acid, ayikwazi ukubhekwa njenge-provitamin.