Coffee consumption and risk of colorectal cancer: a meta-analysis of observational studies

Objective: Separate meta-analyses based on case-control and cohort studies have reported different results on the relationship between coffee consumption and colorectal cancer risk. To clarify the effect of coffee intake on colorectal cancer risk, we performed a meta-analysis based on both case-control and cohort studies. Design: Review study. Setting: We identified case-control and cohort studies related to coffee consumption and colorectal cancer risk listed on MEDLINE, the Cochrane Controlled Trials Register, EMBASE, Science Citation Index and PubMed (until May 2011). Subjects: Research literature on the relationship between coffee consumption and colorectal cancer risk. Results: Twenty-five case-control (15 522 cases) and sixteen cohort studies (10 443 cases) were included in the meta-analysis. Comparing the highest v. the lowest/non category of coffee consumption, the combined results from case-control studies showed a significant relationship with colorectal cancer (OR=0.85, 95% CI 0.75, 0.97) and colon cancer (OR=0.79, 95% CI 0.67, 0.95), but not rectal cancer (OR=0.95, 95% CI 0.79, 1.15). For cohort studies, there was a slight suggestion of an inverse association with colorectal cancer (relative ratio=0.94; 95% CI 0.88, 1.01) and colon cancer (OR=0.93, 95% CI 0.86, 1.01), rather than rectal cancer (OR=0.98, 95% CI 0.88, 1.09). In subgroup analyses using case-control studies, significant inverse associations were found in females for colorectal cancer and in Europe for colorectal and colon cancer, while the subgroup analyses of cohort studies found that coffee drinks substantially decreased risk of colon cancer only in Asian women. Conclusions: Results from case-control studies suggest coffee consumption can significantly decrease the risks of colorectal cancer and colon cancer, especially in Europe and for females.