There is convincing laboratory evidence that calcium reduces the risk of colorectal cancer, but previous epidemiologic studies have reported somewhat inconsistent results. A. recent large prospective study confirms that higher calcium intake is associated with a modestly reduced risk of distal colorectal cancer. There was little additional risk reduction associated with consumers of more than 700 mg calcium/day. This study also suggests that certain subgroups, such as males, smokers, and people who consume low, levels of vitamin D, may be at differential risk. Because colon cancer is a common disease, even a modest decrease in risk has the potential for preventing a substantial number of cases.