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Antioxidant supplements and mortality.

To the Editor: Based on their meta-analysis of antioxidant supplementation trials, Dr Bjelakovic and colleagues 1 conclude that some of the intervention nutrients appeared to be associated with increased mortality. Particular aspects of their approach, analysis, and reported findings may have led to incomplete or biased determinations of the real effect of such nutrients in various populations. Although vitamin A is related to beta carotene (and other provitamin A carotenoids) by virtue of its in vivo formation through oxidative cleavage of the latter, it is not considered an antioxidant nutrient. 2 Its primary inclusion in the meta-analysis, except as an eligible trial cosupplement, is therefore surprising, with specific implications for the 2 trials that tested vitamin A only. Controlled trials of several other nonantioxidant vitamins could have been similarly included in the analysis along with those testing vitamin A. Nearly half of the studies originally identified from the literature (405 of 815) were excluded because no deaths occurred , and most of the 68 trials that were analyzed were small, with few deaths (12 trials had only 1 death). This would yield findings heavily weighted by a few large studies. Also, it would be useful to know what hypotheses formed the basis for the " preconceived " subgroup analyses that excluded selenium and high-bias risk trials, which showed essentially protective effects and whose exclusion would certainly shift the risk estimates higher. The findings from this analysis have implications primarily for supplementation in high-risk populations. Sixty-nine percent of the studies involved secondary prevention and tested efficacy for recurrence or advancement of preexisting cardio-vascular, neoplastic, neurological, ocular, and other diseases. Even of the 21 primary prevention trials, many encompassed elevated baseline population risks from smoking, 3 asbestos exposure, 4 or multinutritional deficiencies, 5 for example. The population risk-antioxidant-mortality interaction might be more clearly elucidated if the respective summary relative risk (RR) estimates for the primary and secondary prevention trials were provided. Also, is it possible that primary vs secondary prevention trials did not significantly differ with respect to mortality in the models, as stated on page 847, when according to the article's Figures 2 and 3 and Tables 1 and 2, these studies had median crude mortality rates of 2.1 and 6.0 deaths per 100 participants (or median crude annual rates of 0.9 and 3.3 deaths per 100 person-years), respectively? Mortality in ran-domized trials of antioxidant supplements for primary and secondary prevention: …