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Reply to HJ Kayden and T Wisniewski

Veterans Administration Medical Center and the University Of Minnesota Research Service 151 Minneapolis, MN 55417 E-mail: vatas001{at}maroon.tc.umn.edu

Dear Sir:

Kayden and Wisniewski suggested that the ratio of biologic activities of RRR--tocopherol to all-rac--tocopherol should be 2.0 in humans, in contrast with the value of 1.36 that we used in our review. The support for this statement was an earlier study reported by Burton et al (1). We did, in fact, cite the article by Burton et al in our review (2); apparently, Kayden and Wisniewski would like to see that article used as the defining study showing that the ratio should be 2.0.

The goal of our review was to give the readers an overview of some of the recent studies that used high doses of vitamin E for the treatment of selected human neurologic disorders. We included a brief introduction on the nomenclature and the biological activities of the various vitamin E compounds as one section of the review. Discussing the merits of the different potential values for the biological activities of the various tocopherol compounds was not one of the main themes of the article. Under the circumstances, we believed that we should use the most widely accepted numbers for the biological activities of the different compounds. The standard sources of information for this type are publications such as The United States Pharmacopeia and The National Formulary, as well as the recommended dietary allowances published by the National Academy of Sciences. The information given in our review is in accordance with such publications. Incidentally, the latest edition of The United States Pharmacopeia (USP 24), which became official on January 1, 2000, gives a ratio of 1.36 (3). Thus, this number is not as "old-fashioned" as claimed by Kayden and Wisniewski. We would like to alert readers that the National Academy of Sciences is currently preparing a new set of dietary reference intakes for vitamin C, vitamin E, selenium, and the carotenoids. Up-to-date information on the biological activities of the tocopherols will be available from this source as well.

Let us also keep in mind that investigators such as Cohn (4) raised some interesting questions about the study by Burton et al. At the very least, we take this as an indication that additional studies comparing the biological availabilities and activities of the various tocopherol compounds are needed. Such investigations may indeed confirm the results of Burton et al. We do maintain that recommendations on the biological potencies of important nutrients such as vitamin E should be changed only after several types of studies have confirmed the need for such an action.

We would like to thank Kayden and Wisniewski for bringing 2 other articles to the attention of the readers, including one by the writers and their colleagues on tocopherol transfer protein in the brain. We are certain that we may have missed some other articles because we attempted to do a selective and not a comprehensive review in the interests of writing a review of manageable size.

_REFERENCES

1. Burton GW, Traber MG, Acuff RV, et al. Human plasma and tissue -tocopherol concentrations in response to supplementation with deuterated natural and synthetic vitamin E. Am J Clin Nutr 1998;67:669–84.[Abstract]
2. Vatassery GT, Bauer T, Dysken M. High doses of vitamin E in the treatment of disorders of the central nervous system in the aged. Am J Clin Nutr 1999;70:793–801.[Abstract/Free Full Text]
3. United States Pharmacopeial Convention. Vitamin E. In: The United States pharmacopeia and the national formulary. Rockville, MD: United States Pharmacopeial Convention, Inc, 2000:1747–9.
4. Cohn W. Evaluation of vitamin E potency. Am J Clin Nutr 1999; 69:156–7 (letter).[Free Full Text]

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