Drinking three or more cups of coffee a day can cut the risk of colon cancer in half—but the benefit manifests itself only in women. What's more, Reuters reports, the research was conducted in Japan, where men drink and smoke so much that scientists had trouble controlling for those factors.
Male subjects in the pool of more than 96,000 people showed no significant drop in colon cancer incidence. The reason for the effect on women isn't known; green tea does not have the same benefits. A research team member speculated that the effect may be related to caffeine, which stimulates the bowel, or to the effect of antioxidants.