Among the nutrients required for the many physiologic functions essential to life are the vitamins.
The vitamin are defined as relatively low molecular weight compounds which humans and for matter, any living organism that depends on organic matter as a source of nutrients.
While the vitamins do not serve structural functions nor does their catabolism provide significant energy, , they do furnish the aerials from which the endocrine glands produce their specific secretions, upon which all the psychological function of the body depend.
Traditionally they are classified according to their solubility water and fat. Solubility confers on vitamins many of their characteristics, it determines how they are absorbed into and transport around by the blood stream, whether they can be stored in the body, and how easily they are lost from the body.
Vitamins consist of a mixed group of chemical compounds and are not related to each other as are protein, carbohydrate and fats.
In general however, physiologically function tends to be limited to one active form to which the related forms are converted. It is essential, also usually in minute amounts, for normal physiological function (i.e. maintenance, growth, development, or production.)
Whether a substance must be supplied intact to the cell or can be synthesized by the cell depends on the assortment of enzymes peculiar to the cell species.
With few exception humans cannot synthesize most vitamins and therefore need to obtain them from food and supplements.
Certain vitamin occur in foods in a form known as precursors or provitamins, Once inside the body, these are transitioned chemically to one or more active vitamin forms.
Definition of Vitamin
