Vitamin E

Vitamin E includes eight naturally occurring compounds divided into tocopherols and tocotrienoles. The most active compound and the most widely available in food is the natural isomer d- (or RRR) α-tocopherol, which accounts for 90% of vitamin E in the human body. Vegetables and seed oils, including soya bean, saffron, sunflower, cereals and nuts, are the main sources. Animal products are poor sources of the vitamin.

Vitamin E is absorbed with fat, transported in the blood largely in low-density lipoproteins (LDL).

An individual's vitamin E requirement depends on the intake of polyunsaturated fatty acids (PUFAs). Since this varies widely, no daily requirement is given in the UK. The requirement stated in the USA is approximately 7-10 mg per day, but average diets contain much more than this. If PUFAs are taken in large amounts, more vitamin E is required.

Function

The biological activity of vitamin E results principally from its antioxidant properties. In biological membranes it contributes to membrane stability. It protects cellular structures against damage from a number of highly reactive oxygen species, including hydrogen peroxide, superoxide and other oxygen radicals. Vitamin E may also affect cell proliferation and growth.

Vitamin E deficiency

The first deficiency to be demonstrated was a haemolytic anaemia described in premature infants. Infant formulations now contain vitamin E.

Deficiency is seen only in children with abetalipoproteinaemia and in patients on long-term parenteral nutrition. The severe neurological deficit (gross ataxia) can be prevented by vitamin E injection.

Plasma or serum levels of α-tocopherol can be measured and should be corrected for the level of plasma lipids by expressing the value as per milligram of plasma lipid or cholesterol.