Soy Isoflavone Intake and Bladder Cancer Risk in Japan: From the Takayama Study

Background: There is growing evidence suggesting that soy isoflavones play a protective role in the development of cancer. However, few epidemiological studies have investigated the association between soy isoflavone intake and bladder cancer.Methods: We evaluated the associations of soy and isoflavone intakes with bladder cancer incidence in a population-based prospective study in Japan. Subjects were 14,233 men and 16,584 women age 35 years or older in September 1992. Soy and isoflavone intakes were assessed via a validated food-frequency questionnaire, while controlling for total energy intake. Cancer incidence was mainly confirmed through regional population-based cancer registries. Bladder cancer was defined as code C67 according to the International Classification of Diseases and Health Related Problems, 10th Revision.Results: During mean follow-up of 13.6 years, 120 men and 41 women had developed bladder cancer. After adjustments for multiple confounders, compared with the lowest quartile of soy food intake, the estimated hazard ratios for the second, third, and highest quartiles of soy food intake were 0.74, 0.52, and 0.55, respectively, in men (P-trend: 0.023). The corresponding values were 0.60, 0.75, and 0.64, respectively, in women (P-trend: 0.43). Similar inverse associations were observed between isoflavone intake and bladder cancer risk.Conclusions: A significant decreased risk of bladder cancer was observed among men who had higher intakes of total soy and isoflavones.Impact: Our finding on the potential benefit of consuming soy foods against bladder cancer is promising and warrants further studies. Cancer Epidemiol Biomarkers Prev; 27(11); 1371-5. ©2018 AACR.