Coffee is not significantly associated with a decreased risk of colorectal, colon, or rectal cancer, contrary to the results of previous trials that found a possible protective effect of coffee against these cancers, according to the results of a review of studies published in the International Journal of Cancer.

"An inverse association between coffee consumption and the risk of colorectal cancer has been found in several case-control studies," but the association was not consistent in prospective cohort studies, which are designed differently, Dr. Youjin Je, of Harvard School of Public Health, Boston, and colleagues note.

Case-control studies include patients with a disease or condition who are compared with "controls," healthy individuals matched up with the study group for factors such as age and sex to avoid bias. Prospective cohort studies are studies in which the participants the have a certain characteristic in common, such as smoking habit or birth order, are identified and then followed forward in time; the final outcome is unknown to the researchers before the trial ends.

The researchers conducted a systematic review of prospective cohort studies to examine the association between coffee consumption and colorectal cancer. They identified 12 studies that included a total of 646,848 participants and 5403 patients with colorectal cancer.

The combined result of the studies, comparing high versus low coffee consumption categories, revealed no significant association between coffee consumption and colorectal cancer risk.

When four studies conducted in the United States were considered, along with five studies conducted in Europe and three Japan, there was no relationship between cancer and coffee consumption and the data from each country were very similar.

Overall, there were no significant differences by sex and cancer site. However, there was a slight inverse association between coffee consumption and colon cancer in women who had a 21 percent reduced risk. This was especially true among Japanese women who had a 38 percent reduced risk.

Studies that analyze the data accounting for the effects of smoking and alcohol use and those with shorter follow-up showed stronger inverse associations between coffee consumption and colorectal cancer.

"Since any effect of coffee intake on colorectal cancer risk could vary by regular or decaffeinated coffee and boiled or filtered coffee, further investigation regarding type- and preparation method-specific analyses is warranted," Je's team comments.