Meta-analysis of coffee consumption and risk of colorectal cancer.

Several studies have found that coffee consumption is related to a lower risk of colorectal cancer, but results have not been consistent. Thus, a meta-analysis of the published articles was conducted to examine this relation. Because of the various ways data were collected and analyzed, a "semiquantitative" approach that compared the high versus the low category of intake for each study was used. The combined results from 12 case-control studies showed an inverse association between coffee consumption and risk of colorectal cancer (pooled relative risk (estimated by odds ratio) for high vs. low category of coffee consumption (RR) = 0.72, 95% confidence interval (CI) 0.61-0.84); the findings were similar in population-based and hospital-based case-control studies. Five cohort studies did not support an association (pooled RR = 0.97, 95% CI 0.73-1.29). The combined results of all studies were driven largely by the case-control studies, which comprised 85 percent of the cases (RR = 0.76, 95% CI 0.66-0.89). The lower risk of colorectal cancer among substantial coffee drinkers was observed in studies from Asia, Northern and Southern Europe, and North America. The results of this meta-analysis indicate a lower risk of colorectal cancer associated with substantial consumption of coffee, but they are inconclusive because of inconsistencies between case-control and prospective studies, the lack of control for important covariates in many of the studies, and the possibility that individuals at high risk of colorectal cancer avoid coffee consumption. Several ongoing prospective cohort studies, based on extensive dietary questionnaires, may provide important new data to evaluate this hypothesis.