A vitamin is an organic molecule (or a set of molecules contiguously associated chemically, i.e. vitamers) that is an vital micronutrient which an organism needs in little quantities for the proper functional of its metabolism. indispensable nutrients cannot be synthesized in the organism, either at every or not in acceptable quantities, and hence must be obtained through the diet. Vitamin C can be synthesized by some species but not by others; it is not a vitamin in the first instance but is in the second. The term vitamin does not total the three other groups of essential nutrients: minerals, necessary fatty acids, and valuable amino acids. Most vitamins are not single molecules, but groups of linked molecules called vitamers. For example, there are eight vitamers of vitamin E: four tocopherols and four tocotrienols. Some sources list fourteen vitamins, by including choline, but major health organizations list thirteen: vitamin A (as all-trans-retinol, all-trans-retinyl-esters, as wi...