Soy food and isoflavone intake and endometrial cancer risk: the Japan Public Health Center-based prospective study

Objective Compared with western populations, the consumption of soy foods among Japanese is very high and the incidence of endometrial cancer very low. We evaluated the association of soy food and isoflavone intake with endometrial cancer risk in Japanese women. Design Prospective cohort study. Setting Ten public health centre areas in Japan. Population Forty nine thousand one hundred and twenty-one women of age 45–74 years who responded to a 5-year follow-up survey questionnaire. Methods Intakes of soy foods as well as other covariates were assessed in 1995–1998 by a self-administered food frequency questionnaire. Cox proportional hazards regression models were used to estimate hazard ratios (HR) and 95% confidence intervals (CI). Main outcome measure Incidence of endometrial cancer. Results During an average of 12.1 years of follow up, 112 newly diagnosed endometrial cancer cases were identified. Energy-adjusted intakes of soy food and isoflavone were not associated with the risk of endometrial cancer. The multivariate-adjusted HR per 25 g/day increase in the intake of soy food was 1.02 (95% CI 0.94–1.10), and the corresponding value for isoflavone intake per 15 mg/day was 1.01 (95% CI 0.84–1.22). Conclusion In this population-based prospective cohort study of Japanese women, we observed no evidence of a protective association between soy food or isoflavone intake and endometrial cancer risk.