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Soy consumption and prostate cancer risk in men: a revisit of a meta-analysis^1,2,3,4

¹ From the Grand Forks Human Nutrition Research Center, Agricultural Research Service, US Department of Agriculture, Grand Forks, ND (LY), and the Department of Mathematics, Washington University, St Louis, MO (ELS).

² The US Department of Agriculture, Agricultural Research Service, Northern Plains Area is an equal opportunity/affirmative action employer and all agency services are available without discrimination. Mention of trade names or commercial products in this article is solely for providing specific information and does not imply recommendation or endorsement by the US Department of Agriculture.

³ Supported by USDA/ARS research project 5450-51000-032-00D.

⁴ Reprints not available. Address correspondence to L Yan, USDA, ARS, Grand Forks Human Nutrition Research Center, Grand Forks, ND 58202-9034. E-mail: lin.yan{at}ars.usda.gov.

ABSTRACT

Background: Epidemiologic studies have shown that the consumption of soy foods may be associated with a reduction in cancer risk in humans.

Objective: The purpose of this study was to conduct a meta-analysis on the association between soy consumption and prostate cancer risk in men.

Design: We systematically reviewed studies obtained through a thorough Medline literature search and identified 15 epidemiologic publications on soy consumption and 9 on isoflavones in association with prostate cancer risk. We extracted the most adjusted relative risks (RRs) and odds ratios (ORs) of the highest and the lowest reported categories of intake from each study and conducted this analysis using a random-effects model in which studies with smaller SEEs are given greater weight in the summary measure.

Results: Our analysis of studies on soy intake yielded a combined RR/OR of 0.74 (95% CI: 0.63, 0.89; P = 0.01). When separately analyzed, studies on nonfermented soy foods yielded a combined RR/OR of 0.70 (95% CI: 0.56, 0.88; P = 0.01) and those on fermented soy foods yielded a combined RR/OR of 1.02 (95% CI: 0.73, 1.42; P = 0.92). The analysis of studies on isoflavones yielded a combined RR/OR of 0.88 (95% CI: 0.76, 1.02; P = 0.09). Further separate analyses showed a combined RR/OR of 0.52 (95% CI: 0.34, 0.81; P = 0.01) from studies with Asian populations and 0.99 (95% CI: 0.85, 1.16; P = 0.91) from studies with Western populations.

Conclusions: The results of this analysis suggest that consumption of soy foods is associated with a reduction in prostate cancer risk in men. This protection may be associated with the type and quantity of soy foods consumed.

Received for publication September 26, 2008. Accepted for publication January 13, 2009.