A vitamer of a particular vitamin is any of a number of chemical compounds that have a similar molecular structure, each of which shows vitamin activity defined by its different biological properties.[1]
For instance, Vitamin A has six vitamer chemicals that all qualify as vitamin A, each with slightly different properties.[2] Four of them are carotenes, from plant foods like carrots, but the retinol form, from animal foods, is several times as effective in humans, per microgram, than the carotene forms. The carotene forms also cannot be absorbed by cats at all.
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 vitamers of a vitamin. Often for the same reason, the toxicity of vitamers varies by molecule, as is the case with vitamin E.[3]
A set of chemicals may be (but is not always) grouped under an alphabetized vitamin "generic descriptor" title, such as "vitamin A". Other examples of vitamers include cyanocobalamin, hydroxocobalamin, methylcobalamin, and 5-deoxyadenosylcobalamin (adenosylcobalamin—AdoB-12), which are all vitamers of B12, and thus all possess "B12 activity". Another example is that both niacinamide and nicotinic acid (niacin) have vitamin B3 activity.
| Vitamin generic descriptor name |
Vitamer chemical name(s) or chemical class of compounds (list not complete) |
|---|---|
| Vitamin A | Retinol, retinal, and four carotenoids: the carotenes alpha-carotene, beta-carotene, gamma-carotene; and the xanthophyll beta-cryptoxanthin |
| Vitamin B1 | Thiamine, Thiamine pyrophosphate |
| Vitamin B2 | Riboflavin, Flavin mononucleotide (FMN), Flavin adenine dinucleotide (FAD) |
| Vitamin B3 | Niacin, niacinamide |
| Vitamin B5 | Pantothenic acid |
| Vitamin B6 | Pyridoxine, pyridoxamine, pyridoxal, pyridoxal 5-phosphate |
| Vitamin B7 | Biotin |
| Vitamin B9 | Folic acid, folinic acid, 5-Methyltetrahydrofolate |
| Vitamin B12 | Cyanocobalamin, hydroxocobalamin, methylcobalamin, adenosylcobalamin |
| Vitamin C | Ascorbic acid, calcium ascorbate, sodium ascorbate, other salts of ascorbic acid |
| Vitamin D | ergocalciferol (D2), cholecalciferol (D3) |
| Vitamin E | Tocopherols (d-alpha, d-beta, d-gamma, and d-delta-tocopherol), tocotrienols |
| Vitamin K | phylloquinone(K1), menaquinones (K2) |