Soy Consumption and the Risk of Prostate Cancer: An Updated Systematic Review and Meta-Analysis

Abstract

Prostate cancer (PCa) is the second most commonly diagnosed cancer in men, accounting for 15% of all cancers in men worldwide. Asian populations consume soy foods as part of a regular diet, which may contribute to the lower PCa incidence observed in these countries. This meta-analysis provides a comprehensive updated analysis that builds on previously published meta-analyses, demonstrating that soy foods and their isoflavones (genistein and daidzein) are associated with a lower risk of prostate carcinogenesis. Thirty articles were included for analysis of the potential impacts of soy food intake, isoflavone intake, and circulating isoflavone levels, on both primary and advanced PCa. Total soy food (p < 0.001), genistein (p = 0.008), daidzein (p = 0.018), and unfermented soy food (p < 0.001) intakes were significantly associated with a reduced risk of PCa. Fermented soy food intake, total isoflavone intake, and circulating isoflavones were not associated with PCa risk. Neither soy food intake nor circulating isoflavones were associated with advanced PCa risk, although very few studies currently exist to examine potential associations. Combined, this evidence from observational studies shows a statistically significant association between soy consumption and decreased PCa risk. Further studies are required to support soy consumption as a prophylactic dietary approach to reduce PCa carcinogenesis.

Keywords: case-control; cohort; epidemiology; isoflavones; prostate cancer; soy.

Figure A1

Funnel plots for (A) total soy intake and risk of prostate cancer; (B) unfermented soy intake and risk of prostate cancer; (C) fermented soy intake and risk of prostate cancer; (D) genistein intake and risk of prostate cancer; (E) daidzein intake and risk of prostate cancer; and (F) total isoflavone intake and risk of prostate cancer.

Figure A2

Funnel plots for (A) circulating genistein and risk of prostate cancer and (B) circulating daidzein and risk of prostate cancer.

Figure A3

Forest plot for total soy intake and risk of prostate cancer by year of study publication. These associations were indicated as a relative risk (RR) estimate with the corresponding 95% confidence interval (CI).

Figure A4

Funnel plot for total soy intake and risk of advanced prostate cancer.

Figure 1

Literature search and study selection flow chart.

Figure 2

Forest plots for (A) total soy intake and risk of prostate cancer; (B) unfermented soy intake and risk of prostate cancer; (C) fermented soy intake and risk of prostate cancer; (D) genistein intake and risk of prostate cancer; (E) daidzein intake and risk of prostate cancer; and (F) total isoflavone intake and risk of prostate cancer. These associations were indicated as a relative risk (RR) estimate with the corresponding 95% confidence interval (CI).

Figure 3

Forest plots for (A) circulating genistein and risk of prostate cancer; and (B) circulating daidzein and risk of prostate cancer. These associations were indicated as a relative risk (RR) estimate with the corresponding 95% confidence interval (CI).

Figure 4

Forest plots for (A) total soy intake and risk of advanced prostate cancer; and (B) isoflavone exposure and risk of advanced prostate cancer. These associations were indicated as a relative risk (RR) estimate with the corresponding 95% confidence interval (CI).