The term vitamin is used to describe a group of essential micronutrients that generally meet the following criteria:

1. organic compounds (or class of compounds) other than fats, carbohydrates and proteins;
2. natural components of foods, usually present in very small quantities;
3. not synthesized by the body in sufficient quantities to meet normal physiological needs;
4. essential, in very small quantities, for normal physiological function (i.e. maintenance, growth, development and reproduction).
5. its absence or insufficiency produces a specific deficiency syndrome.

Vitamers are the multiple forms of vitamins. Their functions in human health are much broader and often include their participation in gene expression. Subclinical or even less than optimal concentrations of some vitamins may contribute to poorer health outcomes that are not normally associated with vitamin status or intake.