Vitamin E is a fat-soluble vitamin that exists in eight different forms. Each form has its own biological activity, which is the measure of potency or functional use in the body. Alpha-tocopherol (-tocopherol) is the name of the most active form of vitamin E in humans. It is also a powerful biological antioxidant. Vitamin E in supplements is usually sold as alpha-tocopheryl acetate, a form that protects its ability to function as an antioxidant. The synthetic form is labelled 'D, L' while the natural form is labelled 'D'. The synthetic form is only half as active as the natural form. Antioxidants such as vitamin E act to protect the cells against the effects of free radicals, which are potentially damaging by-products of energy metabolism. Free radicals can damage cells and may contribute to the development of cardiovascular disease and cancer. Studies are underway to determine whether vitamin E, through its ability to limit production of free radicals, might help prevent or delay the development of those chronic diseases. Vitamin E has also been shown to play a role in immune function, in DNA repair and other metabolic processes. This book presents leading research on this important topic.