Vitamin E: a reexamination.

An attempt is made to place into proper perspective the relative values of the eight natural forms of vitamin E and the epimers of the synthetic products with regard to their biological activities. Since differences in activities reported are mostly in a function of different rates of biological turnover, feeding a non-alpha-tocopherol compound three times a day would be expected to give a different biological value than if the total were fed once a week or together with alpha-tocopherol. An analysis of data to support an increase in the current RDA for vitamin E is presented. Recent developments on the prolongation of blood clotting time by vitamin E are interpreted from the viewpoint that alpha-tocopherol is oxidized to tocopherylquinone, which is an inhibitor of vitamin K.