Critique of the requirement for vitamin E.

The Food and Nutrition Board of the Institute of Medicine recently published a comprehensive evaluation of antioxidants in human diets that includes dietary reference intakes for vitamin E. The new dietary reference intake is 15 mg (35 mol)/d for adults, which is 50% greater than the generous allowance in the 10th edition of Recommended Dietary Allowances published in 1989. Much of the data interpreted in these publications came from studies sponsored by the Committee of Nutritional Studies at Elgin State Hospital (Elgin, IL) of an earlier Food and Nutrition BOARD: The 50% increase in the recommended dietary allowances for vitamin E is not supported by any new data.

Interpretations of requirements for thiamin, riboflavin, niacin-tryptophan, and vitamin E plus comments on balance studies and vitamin B-6.

Data from the long-term projects sponsored by the Food and Nutrition Board to determine the requirements for thiamin, riboflavin, niacin-tryptophan, and vitamin E are utilized to effect an opinion regarding the recommended dietary allowances for these vitamins. Based upon data obtained during these and subsequent research projects, comments on balance studies, changes in tissue lipids, and the requirements for vitamin B-6 are included. The possibility that antioxidants may have an effect on delaying oncogenesis is discussed.

The promotion of vitamin E.

Investigations that have influenced the promotion of vitamin E supplementation are reviewed. The various forms of vitamin E found in foods and the composition of synthetic vitamin E in common use are described with note of a frequent error of identification made in reports of studies on vitamin E. Recent communications on the use of antioxidants to delay carcinogenesis in animals and in humans are discussed.

Serum concentrations of alpha-tocopherol after ingestion of various vitamin E preparations.

The rat-fetal-resorption test currently is used to assess the biological activity of vitamin E compounds. Previous studies in humans, however, suggest that rat assays underestimate the potency of free tocopherol relative to the acetate ester form and of RRR-alpha-tocopheryl acetate relative to all-rac-alpha-tocopheryl acetate. Therefore, we studied the serum concentrations of alpha-tocopherol after ingestion of RRR-alpha-tocopheryl acetate, all-rac-alpha-tocopheryl acetate, RRR-alpha-tocopherol, RRR-alpha-tocopheryl succinate, and RRR-alpha-tocopheryl acetate plus apple pectin by each of 20 adult human subjects.

Relative biological values of d-alpha-tocopheryl acetate and all-rac-alpha-tocopheryl acetate in man.

A reexamination of the biological potency of compounds with vitamin E activities has been made. Special attention has been paid to the relative potencies of d-alpha-tocopheryl acetate and all-rac-alpha-tocopheryl acetate since these two forms provide most of the dietary and clinical supplementations used. Distinctions have been drawn between the vitamin E requirements and metabolism of animals, from which most previous calculations have been made, and the ability of adult males to retain the tocopherols in their blood.

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.

Relationship between levels of blood lipids, vitamins C, A, and E, serum copper compounds, and urinary excretions of tryptophan metabolites in women taking oral contraceptive therapy.

To evaluate which women using oral contraceptive agents might be at risk, biochemical indices known to be affected by the estrogens and progestogens were studied in women who take oral contraceptive agents, in women who do not use oral contraceptive agents, in women in third trimester of pregnancy and 6 weeks after parturition, and in men with normal and high blood lipid levels. The most consistent changes due to oral contraceptive agents were in serum levels of copper, triglycerides, and vitamin A and in the urinary excretion of xanthurenic acid and niacin derivatives before and after a tryptophan load test. There was only a slight suggestion, with no statistical significance, that serum vitamin C levels decreased when the serum levels of ceruloplasmin were high.