By: Joann Bally CSCS
It seems that new studies about what vitamins do or don’t do are often being published. When the press reports on these, they seem to take the approach that the latest study is the best and supersedes whatever went before it. This often is not the case, and the public just gets more confused. Let’s look at one of the more controversial ones.
In the February 28, 2007 issue of the Journal of the American Medical Association we find an article that concludes that antioxidant vitamin supplements, especially beta-carotene, vitamin A, and vitamin E “may increase all-cause mortality.” That is, these vitamins that we thought were good for us, may kill us. Vitamin C and selenium supplements had no effect. Balz Frei, PhD, director of the Linus Pauling Institute, examined this study in the Institute’s Research Newsletter.
Dr. Frei points out that this is a meta-analysis, a statistical analysis of previously published data, that started with 815 human clinical trials but only included 68 in the final meta-analysis. These were further divided into low-bias and high bias trials on arbitrary criteria the authors used to judge the quality of the studies. Although the low-bias trials showed a 5% increased mortality with antioxidant supplements, the high-bias trials showed 9% decreased mortality. Additionally, two large, well-designed trials that showed lower mortality with antioxidant supplements, and had been published in prestigious journals, were arbitrarily excluded.
Dr. Frei further points out limitations of clinical trials for antioxidants, including the problem of measuring oxidative stress and the fact that people would have dietary compounds in their bodies before the tests. Very different dosages were used in the various trials included in the meta-analysis, and of those subjects who did indeed die, there was no pattern in the cause of death.
So it seems that this particular meta-analysis is flawed because of inherent bias and mixing too many types of study and methodologies together. We sometimes find studies, even in important journals, that really do not supersede what we have read previously, but if they have an element of sensationalism, they are likely to be over-reported in the press. There have been studies indicating that antioxidant supplements are beneficial, and these are probably still valid. Dr. Frei recommends you keep taking antioxidant supplements in addition to getting important nutrients from a plentiful intake of fruits and vegetables. We agree. Even in this uncertain world, there is no need to be afraid of your vitamin pills.
The Linus Pauling Institute is on the web at http://lpi.oregonstate.edu. Check out their Micronutrient Information Center for information about vitamins, minerals, and other micronutrients.
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