Association between coffee consumption and risk of bladder cancer in a meta-analysis of 16 prospective studies
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RESEARCH
Open Access
Association between coffee consumption and risk of bladder cancer in a metaanalysis of 16 prospective studies Zhi-Wei Dai1, Ke-Dan Cai1, Fu-Rong Li2, Xian-Bo Wu2 and Guo-Chong Chen3*
Abstract Background: Current evidence remains equivocal as to whether and how consumption of coffee may be associated with risk of bladder cancer, and potential influence of confounding by smoking on this association is yet to be elucidated. We conducted an updated meta-analysis of prospective studies to address these issues. Methods: Relevant studies were identified by searching PubMed and EMBASE databases from inception to April 2019. A random-effects model was used to estimate summary relative risk (RR) with corresponding 95% confidence interval (CI) of bladder cancer associated with coffee consumption. Results: The final analysis included 16 prospective studies comprising 2,122,816 participants and 11,848 bladder cancer cases. Overall, coffee consumption was not associated with risk of bladder cancer (RR high-vs-low = 1.07, 95% CI: 0.96–1.20). The lack of association persisted in the strata defined by sex or participants’ smoking status. Meta-regression analyses identified the number cases (P difference = 0.06) and the degree of adjustment for smoking (P difference = 0.04) as potential sources of heterogeneity. There was an increased risk of bladder cancer related to higher coffee consumption among studies with fewer cases (RR high-vs-low = 1.38, 95% CI: 1.05–1.81) and among those with poorer adjustment for smoking (RR high-vs-low = 1.48, 95% CI: 1.14–1.93). Results were similar in the dose-response analyses (RR 1 cup/d = 1.01, 95% CI: 0.98–1.03). Conclusion: Best evidence available to date does not support an independent association between coffee consumption and bladder cancer risk. Some direct associations observed in individual studies may be a result of residual confounding by smoking. Keywords: Coffee, Bladder cancer, Cohort studies, Meta-analysis
Background Coffee is among the most commonly consumed beverages worldwide. As such, a small impact of coffee drinking on health risk could lead to significant public health consequences. Over the past decades, many epidemiologic studies have been carried out to extensively evaluate potential influences coffee drinking on multiple health outcomes, including the developments of various types of cancer [1]. While inverse associations between coffee consumption and risk of cancers at specific sites including liver and endometrium have been documented [2], some evidence for an * Correspondence: [email protected] 3 Department of Epidemiology and Population Health, Albert Einstein College of Medicine, 1300 Morris Park Avenue, Bronx, NY 10461, USA Full list of author information is available at the end of the article
increased risk of bladder cancer related to coffee drinking also emerged. In 1991, the International Agency for Research on Cancer (IARC) Monographs classified coffee as “possibly carcinogenic” to the bladder [3]. The IARC Monographs review
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