The physiological effects of vitamin E are caused by a series of seven naturally occurring, closely related compounds what are known as tocopherols.
The tocopherols are characteristically soluble in fat solvents and insoluble in water. They are colourless, non-crystallizing oils, stable to heat and acids.
The most important isomers of tocopherol are alpha (?), 5, 7, 8- trimethyltocol; beta (0), 5, 8-dimethyltocol; gamma (y), 7, 8-dimethyl- tocol ; and delta, (8) 8-methyltocol. These differ in their biological activity.
? and y tocopherols differ from the a-form in the positions of the methyl groups attached to the benzene ring. For example, ?- tocopherol has methyl groups only on carbons 5 and 8. The structure formula for a-tocopherol is as follows :
The chemical nature of vitamin E is not yet definite. Evans and Bishop (1922) thought that the above said y tocopherols are very similar in their composition to natural vitamin E and the formula is C29H50O2. It is stable in ordinary light but readily destroyed by ultraviolet light and rancid fat.
Occurrence and availability Vitamin E:
Vitamin E is generally found in some of the natural oils such as wheat germ oil, cotton seed oil, rice germ oil and in the green leaves of lettuce and alfalfa. It is also found in meat, egg yolk, fish liver oil but in poor amount.
Daily requirement: The recommended daily requirement of vitamin E for adults is 30 International Units for men and 25 I. U. for women.
The amount for women is increased to 30 I. U. during pregnancy and lactation. For infants and children, 1 to 125 I. U. per kilogram body weight are recommended.
One International Unit (I. U.) of a-tocopherol is defined as the biologic activity of IT mg of the pure compound (or 0 67 mg a-toco- pherol).