gamma-tocopherol, the major form of vitamin E in the US diet, deserves more attention

Abstract

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