Soy Consumption and the Risk of Developing Bladder Cancer: A Pooled Analysis of Cohort Studies from the International Pooled Bladder Cancer Epidemiology and Nutritional Determinants (BLEND) Study

Background: Epidemiological studies have shown inconsistent results in associations between soy consumption and bladder cancer (BC). Therefore, this research aims to find more conclusive answers on the influence of soy consumption on the development of BC risk by bringing together 12 worldwide available cohort studies on this topic. Materials and Methods: The risk of developing BC was investigated in a pooled analysis of 12 cohort studies comprising 549,458 participants, including 3164 incident BC cases. Cox proportional hazard regression analysis was used to obtain the pooled hazard ratios (HRs) and corresponding 95% confidence intervals (CIs). Results: No association between total soy intake and risk of development of BC was observed. However, after adjustment for potential confounders, soybean oil intake was associated with an increased risk (HRmodel2 = 1.49, 95% CI 1.03–2.16) comparing never consumption with ever consumption as well as with moderate (HRmodel2 1.69, 95% CI 1.08–2.67; HRmodel3 1.65, 95% CI 1.03–2.64) and high (HRmodel2 1.57, 95% CI 1.06–2.33; HRmodel3 1.50, 95% CI 1.00–2.26) consumption. Overall, no significant associations were observed for soybean, soy milk or unfermented soy paste intake. For females a significant decreased BC risk for moderate soybean consumption was observed (HR = 0.46, 95% CI 0.22–0.89). For males a significant increased BC risk in ever soybean oil consumers as well as in high soy consumers was found (HR = 1.63, 95% CI 1.00–2.66; HR = 1.69, 95% CI 1.02–2.80, respectively). Conclusions: This research suggests that different sub-categories of soy consumption may have different associations with BC risk, showing differences between sexes exist.