The tocopherol and tocotrienol subfamilies are each composed of alpha, beta, gamma and delta vitamers having unique biological effects. Different ratios of these compounds are found in anatomically different parts of a plant. For example, the green parts of a plant contain mostly alpha tocopherol and the seed germ and bran contain mostly tocotrienols. Since the original rating method was established, many additional important biological effects of these compounds have been discovered and many nutritional scientists now consider that rating method to be incomplete.
New studies continue to elucidate the unique benefits of individual members of the vitamin E family.
For example, tocotrienols have been shown to lower cholesterol, prevent LDL oxidation, and reduce atherosclerotic plaque formation more effectively than tocopherols. For these and other reasons, the original definition of vitamin E has been enhanced to include all eight family members and the related compounds that convert to them in the body. Vitamin E compounds are usually produced and made available in esterified form as alpha tocopheryl acetate or alpha tocopheryl succinate. Neither of these forms has any antioxidant activity until converted to alpha tocopherol in the body, but they are much more stable with respect to storage time and temperature than the unesterified forms. Moreover, while the acetate form is rapidly activated within the body, activation of the succinate form is slower.