Key clinical point: High intake of soy and isoflavones might be associated with an increased subsequent risk of prostate cancer mortality.

Major finding: A positive association was seen between the intake of soy food and prostate cancer mortality (multivariate hazard ratio [HR] for highest [Q5] vs. lowest quintile [Q1], 1.76; P for trend =.04). A similar association was seen for isoflavones intake (multivariate HR _{Q5 vs. Q1}, 1.39; P for trend =.04).

Study details: This Japanese population-based prospective study included 43,580 men with no history of cancer or cardiovascular disease (aged, 45-74 years) and who were followed-up from 1995 to 2016.

Disclosures: This study was supported by the National Cancer Center Research and Development Fund, Grant-in-Aid for Cancer Research from the Ministry of Health, Labour and Welfare of Japan and the Ministry of Agriculture, Fishery and Forestry, Japan. The authors declared no conflicts of interest.

Commentary

“Several studies have supported a potential association between higher soy and isoflavone intake and decreased prostate cancer incidence. However, there is some evidence that higher isoflavone intake may be associated with more advanced prostate cancer, despite the lower incidence. To further evaluate this finding, Sawada et al. conducted a prospective cohort study in Japanese men with no previous history of cancer. Participants completed a comprehensive and validated questionnaire that asked about 138 food items. During nearly 17 years of follow-up, increased isoflavone and soy intake was associated with an increased risk for prostate cancer death on multivariate analyses, with the hazard ratio (HR) = 1.39 for isoflavones and the HR = 1.76 for soy. While these findings are not practice-changing, they do suggest that these foods could be initially preventative, but once prostate cancer arises, could be somewhat detrimental. Further studies would be needed to further evaluate this hypothesis.”

Mark Klein, MD