Relative vitamin E potency of natural and of synthetic alpha-tocopherol.

A reasonably accurate estimate of the relative physiological value of natural and of synthetic ar-tocopherols is needed by the clinician, the pharmaceutical industry, and the experimental nutritionist to facilitate their use of vitamin E in a more quantitative manner. At present there is preliminary information available for two species of animals. It was tentatively established (1) in 1944 that for rats natural d, cr-tocopherol possessed 50 per cent more potency than synthetic dl ,a-tocopherol, with resorption during gestation as a criterion. In 1947 Hove and Harris reported (2) that for rabbits natural a-tocopherol was 22 per cent more active than the synthetic racemic form, based on effectiveness in curing muscle dystrophy. It is now possible to reevaluate the relative potency of dand of dl, crtocopherol in the rat, based on the results of numerous bioassays in this laboratory since 1944, by means of an improved assay procedure (3). From these data a new value of 1.36, for the ratio of the potency of natural tocopherol to the potency of synthetic tocopherol, has been obtained.