A
vitamer of a particular
vitamin is any of the chemical compounds which exhibit vitamin activity. Very commonly "vitamins" are not single compounds, but rather each
vitamin, which is defined by its biological activity, not its structure, is actually represented by a number of substances, all of which show vitamin activity.
[1] These substances are called vitamers.
Typically, the vitamin activity of multiple vitamers is due to the body's (limited) ability to convert one vitamer to another, or many vitamers to the same enzymatic cofactor(s), which is active in the body as the important form of the vitamin.
As part of the definition of vitamin, the body cannot completely synthesize an optimal amount of vitamin activity from simple foodstuffs, without some minimal amount of a vitamer molecule as a basis.
Typically not all vitamers possess exactly the same vitamin potency, per mass. This is due to differences in absorption and interconversion of the various different vitamers of a vitamin. Often for the same reason, the toxicity of vitamers varies by molecule, as is the case with vitamin E.[2]
