ABSTRACT
Vitamin E was discovered in 1922 as a compound necessary to sustain reproductive ability in rodents. Despite in vitro antioxidant activity of each vitamin E form, whether each form exhibits in vivo antioxidant function is questionable because of considerable differences in bioavailability. Although there are eight forms of vitamin E, only α- and γ-tocopherols are generally detected in tissues and plasma of non-users of dietary supplements. The chapter focuses on the vitamin E forms, although greater emphasis will be placed on α-tocopherol because this is the only form of vitamin E that is essential for humans. Vitamin E is the term that describes eight lipophilic, naturally occurring compounds including four tocopherols and four tocotrienols. Within each class, four forms exist as α-, β-, γ-, and δ- that differ based on the number and position of methyl groups present on the chromanol head. Dietary intakes of α-tocopherol are rarely low enough in the American diet to induce vitamin E deficiency symptoms.
