Submitted to: American Journal of Clinical Nutrition
Publication Type: Peer reviewed journal
Publication Acceptance Date: 1/13/2009
Publication Date: 2/11/2009
Publication URL: http://handle.nal.usda.gov/10113/29266
Citation: Yan, L., Spitznagel, E.L. 2009. Soy Consumption and Prostate Cancer Risk in Men: A Revisit of Meta-Analysis. American Journal of Clinical Nutrition.89:1155-1163. Interpretive Summary: Soy is a major plant source of dietary protein to humans. Epidemiologic studies show that consumption of soy foods may be associated with a reduction in cancer risk in humans. Prostate cancer is the second leading cause of deaths from cancer in American men. We examined the relationship between soy consumption and prostate cancer risk by conducting a statistical analysis of findings from published epidemiologic studies. Results of our analysis of 15 publications showed that soy intake was related to an approximately 26% reduction in prostate cancer risk. Further analysis focused on the types of soy foods consumed and found intake of non-fermented soy foods (e.g. bean curd and soymilk) was related to the risk reduction, whereas fermented ones were not. Results of our analysis of eight studies on isoflavones (a group of bioactive compounds from soy that may be cancer preventive) revealed that consumption of isoflavones was marginally, but not significantly, related to a reduction in prostate cancer risk. Results of this analysis indicate that consumption of soy foods may be associated with a reduction in prostate cancer risk in men.
Technical Abstract: Background: Soy is a major plant source of dietary protein to humans. Epidemiologic studies show that 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 in men. Design: We systematically reviewed studies obtained through a thorough MEDLINE literature search and identified 15 publications (six cohort and nine case-control studies) on soy consumption and eight case-control studies on isoflavone intake in relation to prostate cancer risk. We conducted this analysis using a random-effects model in which studies with smaller standard error of estimate are given greater weight in the summary measure. Results: Our analysis of studies on soy intake yielded an overall risk estimate of 0.74 (95% confidence interval: 0.63, 0.89; P = 0.001). When separately analyzed, studies on non-fermented soy foods yielded an overall risk estimate of 0.70 (0.56, 0.88; P = 0.002) and those on fermented ones yielded 1.02 (0.73, 1.42; P = 0.922). The analysis of studies on isoflavones yielded an overall risk estimate of 0.88 (0.76, 1.02; P = 0.085). When analyzed on the basis of daily isoflavone intakes, we found an overall risk estimate of 0.63 (0.41, 0.96; P = 0.03) from studies at mg/day and 0.99 (0.85, 1.16; P = 0.909) from those at µg/day, respectively. Conclusions: 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.