γ-Tocopherol, the major form of vitamin E in the US diet, deserves more attention

Abstract

γ-Tocopherol is the major form of vitamin E in many plant seeds and in the US diet, but has drawn little attention compared with α-tocopherol, the predominant form of vitamin E in tissues and the primary form in supplements. However, recent studies indicate that γ-tocopherol may be important to human health and that it possesses unique features that distinguish it from α-tocopherol. γ-Tocopherol appears to be a more effective trap for lipophilic electrophiles than is α-tocopherol. γ-Tocopherol is well absorbed and accumulates to a significant degree in some human tissues; it is metabolized, however, largely to 2,7,8-trimethyl-2-(β-carboxyethyl)-6-hydroxychroman (γ-CEHC), which is mainly excreted in the urine. γ-CEHC, but not the corresponding metabolite derived from α-tocopherol, has natriuretic activity that may be of physiologic importance. Both γ-tocopherol and γ-CEHC, but not α-tocopherol, inhibit cyclooxygenase activity and, thus, possess antiinflammatory properties. Some human and animal studies indicate that plasma concentrations of γ-tocopherol are inversely associated with the incidence of cardiovascular disease and prostate cancer. These distinguishing features of γ-tocopherol and its metabolite suggest that γ-tocopherol may contribute significantly to human health in ways not recognized previously. This possibility should be further evaluated, especially considering that high doses of α-tocopherol deplete plasma and tissue γ-tocopherol, in contrast with supplementation with γ-tocopherol, which increases both. We review current information on the bioavailability, metabolism, chemistry, and nonantioxidant activities of γ-tocopherol and epidemiologic data concerning the relation between γ-tocopherol and cardiovascular disease and cancer.