Coffee drinking and colorectal cancer risk: an evaluation based on a systematic review and meta-analysis among the Japanese population

Objective: It remains unclear whether coffee drinking is associated with colorectal cancer risk. We performed a systematic review and meta-analysis of epidemiologic studies on this issue among the Japanese population. Methods: Original data were obtained from MEDLINE searches using PubMed or from searches of the 'Ichushi' database, complemented with manual searches. Meta-analysis was performed by using the random effects model to estimate the summary relative risk with 95% confidence interval according to the study design. The final judgment was made based on a consensus of the research group members with consideration for both epidemiological evidence and biological plausibility. Results: We identified five cohort studies and nine case-control studies. Of these, one cohort study reported a strong inverse association ( in women only), whereas three case-control studies reported a strong inverse association with colon or rectal cancer. In meta-analysis, high consumption of coffee was not appreciably associated with colorectal cancer risk among cohort studies, whereas it was associated with significantly lower risk of colorectal or colon cancer among case-control studies. The summary relative risk/odds ratio ( 95% confidence interval) for the highest versus lowest categories of coffee consumption was 0.95 ( 0.77-1.17) and 0.78 ( 0.65-0.95) for cohort and case- control studies, respectively. Conclusions: The evidence is insufficient to support that coffee drinking increases or decreases the risk of colorectal cancer among the Japanese population.