Vitamin are chemically unrelated organic substances that are grouped together because each is essential in the diet in minute amounts and is required for specific metabolic reactions within the cells.
Traditionally they are classified according to their solubility water and fat solvents and, from a physiological standpoint; this property determines the pattern of transport excretion and storage within the human body.
Several of the vitamins, while conveniently considered as a single substance, actually are a group of structurally related compound that tend to behave alike physiologically.
In general however, physiologically function tends to be limited to one active form to which the related forms are converted.
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.
A substance, therefore, may be a vitamin for one species but not for another. The difference lies whether the substances is required in the diet or whether it can be synthesized by human body.
Vitamin in general
