It is a fat-soluble vitamin. It is also known as tocopherol.
Since 1922 effects of vitamin E deficiency was studied in rats. When Bishop and Evans announced the existence of a substance X, the absence of which in the diet, results failure in the reproductive capacity of rats. In 1936 Evans and Emerson isolated and synthesized vitamin E from the unsaponifiable fraction of wheat germ oil, which was found ti, be a mixture of three closely related compounds. A fourth was discovered in 1955, and recently two other compounds have been detected.
There are three varieties of tocopherols- ά, β and γ. They are unsaturated alcohols. The most active compound is ά, tocopherol. They are soluble in fat and fat solvents, heat stable and exist naturally as yellow oil. They are excellent antioxidants. They prevent other vitamins present in food (e.g. vitamin A) from oxidative destruction. Free tocopherols and their esters are readily absorbed from the small intestine. Bile acids are necessary for absorption.
Important sources of vitamin E:
Vitamin E is widely distributed in foods. By far the richest sources are vegetable oils, cottonseed, sunflower seed, egg yolk and butter. Foods rich in polyunsaturated fatty acids are also rich in vitamin E. animal sources rich in vitamin A are egg, milk, fish and muscles. Vegetable sources are vegetable seed oils, especially wheat, soyabean, corn and leafy vegetables.
Functions of vitamin E
Tocopherols have got antioxidative effects and prevent unwanted oxidation in the body. Essential for normal functions of the muscle. Deficiency produces muscular dystrophy. It acts as a cofactor in the electron transfer system operating between cytochromes b and c. vitamin e has something to do with the reproductive functions of the body. It also has some effect upon the heart. Per oxidation and brown pigmentation due to formation of highly unsaturated fatty acids are prevented by the tocopherols. Massive necrosis of the liver produced by the deficiency of sulphur containing amino acids and selenium are also prevented by tocopherols. The development of encephalomalacia in chicks (cerebellar disorder) and exudative diathesis is due to deficiency of vitamin E and is relieved by administration of tocopherols. It is necessary for normal development of the early embryo.
Daily requirement:
Average daily intake through normal diet is about 15 to 20 mgm, which satisfies the requirement.
Deficiency signs of vitamin E
Deficiency is said to cause sterility in males (loss of seminiferous epithelium), abortion in females (death of the foetus in utero and its resorption) and diminished milk secretion. Probably it is a preventive of pregnancy toxemia. Excessive intake does not increase fertility but may cure sterility. Its deficiency produces atrophy of testes and spermatogenic failure and both of which are irreversible in prolonged deficiency. Erythrocytes are affected in vitamin E deficiency. Combined deficiency of this vitamin and selenium (Se) produces hepatic necrosis. In the female implantation of the ovum occurs, but after some time the foetus dies due to deficiency of vitamin E. vitamin E therapy is of some importance in the prevention of habitual miscarriage in women. In the deficiency of vitamin E there are changes in the cardiac muscle indicating degenerative lesions. In the absence of vitamin E, the quantity of unsaturated fats in the cells becomes diminished, causing abnormal structure and function of such cellular organelles as the mitochondria, the lysosomes and even the cell membrane. Deficiency of vitamin E prevents normal growth and sometimes causes degeneration of the renal tubular cells and the muscle cells.
Recently the cytotoxic effect of vitamin E on human lymphocytes in vitro at high concentrations has been reported. This being so, caution should be exercised against the mega dose consumption of vitamin E in clinical practice.
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