Dietary patterns and risk of bladder cancer: a systematic review and meta-analysis

Background Several studies have investigated the relationship between dietary patterns and the risk of bladder cancer (BC) in different regions including Europe, the United States, and Asia, with no conclusive evidence. A meta-analysis was undertaken to integrate the most recent information on the relationship between a data-driven Western diet (WD), the Mediterranean diet (MD), and dietary-inflammatory-index (DII) and the risk of BC. Method We looked for published research into the relationship between dietary patterns and the incidence of BC in the PubMed/Medline, Cochrane Library, Web of Science, and Scopus databases up until February 2021. Using a multivariate random-effects model, we compared the highest and lowest categories of WD, MD and DII patterns and provided the relative risk (RR) or odds ratios (OR) and 95 percent confidence intervals (CIs) for the relevant relationships. Results The analysis comprised 12 papers that were found to be suitable after scanning the databases. Both case-control (OR 0.73, 95% CI: 0.52, 0.94; I-2 = 49.9%, n = 2) and cohort studies (RR 0.93, 95% CI: 0.88, 0.97; I-2 = 63%, n = 4) found a substantial inverse association between MD and BC. In addition, although cohort studies (RR 1.53, 95% CI 1.37, 1.70; I-2 = 0%, n = 2) showed a direct association between WD and BC, case-control studies (OR 1.33, 95% CI 0.81, 1.88; I-2 = 68.5%, n = 2) did not. In cohort studies, we found no significant association between DII and BC (RR 1.02, 95% CI 0.93, 1.12; I-2 = 38.5%, n = 2). In case-control studies, however, a strong direct association between DII and BC was discovered (RR 2.04, 95% CI 1.23, 2.85; I-2 = 0%, n = 2). Conclusion The current meta-analysis showed that MD and WD have protective and detrimental effects on BC risk, respectively. No significant association between DII and the risk of BC was observed. More research is still needed to confirm the findings. Additional study is warranted to better understand the etiological mechanisms underlying how different dietary patterns affect BC.