Dietary soy and increased risk of bladder cancer: A prospective cohort study of men in Shanghai, China

Abstract

To verify our previous finding of a positive association between dietary soy and bladder cancer risk, we examined the association in a second, geographically distinct prospective cohort of Chinese subjects, the Shanghai Cohort Study. Briefly, 18,244 men aged 45-64 years were recruited between January 1986 and September 1989. As of December 31, 2002, 61 incident bladder cancer cases were identified. Information on soy consumption was obtained through inperson interviews at baseline using a food frequency questionnaire. Cox proportional hazard regression methods were used to estimate relative risks (RR) and their corresponding 95% confidence intervals (CI), with adjustment for age (years) at baseline interview, level of education and other potential confounders. Compared to men consuming soy less than once a week, the RR (95% CI) for those who consumed soy I-<3 times per week, 3-<7 times a week and daily were 2.05 (0.80-5.29), 2.45 (0.89-6.76) and 4.61 (1.57-13.51), respectively (p for trend = 0.004), after adjustment for age, cigarette smoking and level of education. The soy-bladder cancer risk associations in smokers and non-smokers were comparable. The soy-bladder cancer relationship became stronger when the analysis was restricted to subjects with 2 or more years of follow-up. © 2004 Wiley-Liss, Inc.