Milk and Dairy Product Consumption and Bladder Cancer Risk: A Systematic Review and Meta-Analysis of Observational Studies.

Some studies have reported that milk and dairy product consumption reduces bladder cancer incidence, whereas others have reported null or opposite findings. This meta-analysis of 26 cohort and case-control studies has been conducted to pool the risk of the association between milk and dairy products and bladder cancer. A systematic search in MEDLINE, EMBASE, and the Web of Science (from inception to 30 April 2018) was conducted. Random-effects models were used to compute pooled estimates of RR for high or medium compared with low consumption of milk and dairy. Sensitivity analyses were conducted. Subgroup analyses were performed based on type of dairy, gender, geographic location, and type of study design. Random-effects meta-regression was used to evaluate other confounding factors. Overall, medium compared with low consumption was associated with lower pooled risk of bladder cancer for total dairy products (RR = 0.90; 95% CI: 0.81, 0.98), milk (RR = 0.90; 95% CI: 0.82, 0.98), and fermented dairy products (RR = 0.87; 95% CI: 0.79, 0.96). The inverse association for milk consumption was stronger in Asians (RR = 0.79; 95% CI: 0.59, 0.98) and in cohort design studies (RR = 0.85; 95% CI: 0.71, 0.99). Moreover, high compared with low consumption was significantly associated with a lower pooled risk for milk (RR = 0.89; 95% CI: 0.81, 0.98) and fermented dairy products (RR = 0.78; 95% CI: 0.61, 0.94). However, high compared with low consumption of whole milk was significantly associated with a higher risk (RR = 1.21; 95% CI: 1.04, 1.38). The statistical heterogeneity was considerable. In conclusion, the present meta-analysis suggests a decreased risk of bladder cancer associated with medium consumption of total dairy products and with medium and high consumption of milk and fermented dairy products. An increased risk of bladder cancer was observed with high consumption of whole milk. Interpretations of the results should be made with caution. This review was registered at www.crd.york.ac.uk/prospero as CRD42018097020.