Comments on the new dietary reference intake for vitamin E

Scientist Emeritus National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health 3612 Pimlico Place Silver Spring, MD 20906 E-mail: johnbieri{at}webtv.net

Dear Sir:

I am writing in response to the editorial by Traber (1) and the article by Horwitt (2). I agree with Horwitt that the "50% increase in the recommended dietary allowances for vitamin E is not supported by any new data."

Traber states that the new dietary reference intake is based on the in vitro erythrocyte hemolysis test because this test was used in Horwitt's Elgin Project studies. The peroxide hemolysis test entails a highly variable procedure, which Horwitt (3) clearly emphasized. He stated, "the concentration of the hydrogen peroxide, the rate at which it is added to the erythrocyte suspension, the temperature, and the elapsed time of incubation all can have large effects on the hemolysis obtained." He also pointed out that "one can easily choose conditions at which all normal blood would hemolyze or, conversely, where no deficient blood would hemolyze."

Other investigators have also reported the many variables that can affect the hemolysis test (4). Horwitt (3) further stated that "this choice [0.5 mg/100 ml] is fortuitous since one does not obtain signs of a more rapid erythrocyte turnover in subjects that have as much as 0.5 mg/100 ml of tocopherol in their blood."

Traber justifies the elimination of -tocopherol in the assessment of dietary vitamin E because there is no known transport protein for this vitamer. Because -tocopherol has been shown to have biological activity in all species tested (5), it seems inconceivable that humans should not benefit from this form of vitamin E. Healthy human blood contains significant concentrations of -tocopherol, even without (presumably) a specific transport protein. In summary, the establishment of a dietary reference intake for vitamin E on the basis of "the best data currently available," as Traber states, should not discount the best data of the past.

REFERENCES

1. Traber MG. Vitamin E: too much or not enough? Am J Clin Nutr 2001;73:997–8.
2. Horwitt MK. Critique of the requirement for vitamin E. Am J Clin Nutr 2001;73:1003–5.
3. Horwitt MK. Interpretation of human requirements for vitamin E. In: Machlin LJ, ed. Vitamin E, a comprehensive treatise. New York: Marcel Dekker, 1980:621–36.
4. Farrell, PM. Human health and disease. In: Machlin LJ, ed. Vitamin E, a comprehensive treatise. New York: Marcel Dekker, 1980:520–620.
5. Bieri JG, Poukka-Everts R. Gamma tocopherol: metabolism, biological activity and significance in human vitamin E nutrition. Am J Clin Nutr 1974;27:980–6.