Linus Pauling Institute

Natural (RRR) or synthetic (all-rac) forms of alpha-tocopherol are available (usually as acetate esters) for use as vitamin E supplements. In animal tests, the natural stereoisomer, RRR-alpha-tocopheryl acetate, is 1.36 times more biologically potent than all-rac-alpha-tocopheryl acetate, an equimolar mixture of eight stereoisomers [8,15,40-43]. The higher biologic activity of natural compared with synthetic vitamin E does not result from differences in antioxidant activity [2,3], but could hypothetically be explained by differences in (1) absorption, (2) plasma transport, (3) delivery to tissues, or (4) metabolism. These possibilities will be considered in this review.