点击显示 收起
Department of Biochemistry & Program in Nutrition
Emory University
Atlanta, GA 30322
E-mail: biocdbm{at}emory.edu
Dear Sir:
The letter by Hathcock, an advocate of the dietary supplement industry, attempts to question the accuracy of the assumptions in my editorial (1) and their relevance to the meta-analysis by Bleys et al (2). In the first place, I made no assumptions but simply related the essence and background of that report. Careful perusal of both my editorial and the report show that Bleys et al extensively reviewed the literature to identify those studies that were randomized controlled clinical trials of vitamin and mineral use in the prevention or treatment of atherosclerosis. Moreover, they provided an appendix of online supplemental data and their search strategy. It was obvious from a review of these data that many of the reports identified had design flaws. No doubt, some of these studies proposed benefits of multivitamin-mineral use, whereas others did not.
The conclusion that Bleys et al reached, based on an analysis of those studies that were screened and deemed properly controlled, provided, according to the authors, "no evidence for a protective effect of antioxidant or B-vitamin supplements on the progression of atherosclerosis, thus providing a mechanistic explanation for their lack of effect on clinical cardiovascular events." Hathcock's claim that the report by Bleys et al "is not an accurate reflection of the literature" because their analysis failed to include findings from the Women's Health Study (3) is clearly off the mark given the conclusions of that study. As noted in the Annual Bibliography of Significant Advances in Dietary Supplement Research 2005 (4), "Overall, this study with its large sample size and long duration does not support the use of vitamin E to prevent CV disease or cancer in women." The findings of the HOPE and HOPE TOO trial investigators, which were also summarized in the Annual Bibliography of Significant Advances in Dietary Supplement Research 2005, were similar: "The investigators concluded that long-term vitamin E therapy does not prevent cancer or cardiovascular events and may even increase the risk of heart failure in individuals with existing disease."
Despite Hathcock's assertions, the meta-analysis remains a useful tool, although certain conclusions are best secured, as in any analysis, when the data set is large. It is additionally informative to consider the results of testing of single micronutrients and combinations of micronutrients, as were summarized in the reports by Alberg et al and by Huang et al in the Conference on Multivitamin/Mineral Supplements, which was held in May of 2006 (5). Alberg et al stated, "With few exceptions, the available evidence from RCTs (randomized clinical trials) of ß-carotene, vitamin E, vitamin A (in combination with zinc or ß-carotene), or combined riboflavin and niacin indicates no consistent benefit of these single or paired nutrients in preventing cancer, cardiovascular disease, cataract or age-related macular degeneration." Huang et al stated, "The overall strength of evidence on the efficacy of multivitamin/minerals for the prevention of chronic disease is rated as very low."
Certainly, there has been no attempt to misconstrue or prejudge present reports insofar as they represent carefully controlled studies. The number of reports currently available in the literature that disavow the previously hyperbolic claims of benefits from supplements in preventing and treating nondeficiency diseases is growing and should receive careful consideration. Additional studies that provide unbiased interpretations are needed. What is not needed is the disservice of those who, for misguided intentions, mislead the public into practices not based on facts.
ACKNOWLEDGMENTS
The author reported no conflict of interest.
REFERENCES