As any nutritional text dated prior to 1970 will indicate, vitamin E has not received much respect from nutritionists. In such texts it is often placed after vitamin K, in the miscellaneous category. This is because it took a good 40 years from its discovery in 1923 (Evans and Bishop 1923) to demonstrate a clear-cut human deficiency disease for vitamin E. Though numerous studies had shown vitamin E to be an essential component of animal diets, deficiency symptoms varied from one species to the next, from reproductive disorders in rats to vascular abnormalities in chickens. Thus, it was not clear that humans had an obligatory requirement for vitamin E. Recent research, however, has shown that this is indeed the case and that vitamin E is just as important to human nutrition as the other vitamins. It is, therefore, pleasing to see that vitamin E is now placed in its proper place in the alphabet of vitamins.

Vitamin E is the nutritional term used to describe two families of four naturally occurring compounds each, the tocopherols and the tocotrienols (Pennock, Hemming, and Kerr 1964). Tocopherols and tocotrienols both contain a chroman ring, which is essential for biological activity, but differ in the degree of saturation of their fatty side chains. They are otherwise interchangeable in their biological role. Each family comprises alpha, beta, gamma, and delta forms, which differ significantly in their potency. Thus, alpha-tocopherol represents the principal source of vitamin E found in the human diet with a small contribution also coming from gamma-tocopherol (Bieri and Evarts 1973). Many texts, including this one, use the terms alpha-tocopherol and vitamin E interchangeably.