Calcium and the prevention of colon cancer

Diet is a major determinant of colon cancer risk. Calcium may protect against colon cancer, presumably by binding cytotoxic bile acids and fatty acids. Numerous studies support this proposition. In subjects at risk for colon cancer oral calcium supplementation has been shown to reduce rectal epithelial proliferation rate, thereby supposedly decreasing cancer risk. In contrast to the original hypothesis that phosphate counteracts the effect of calcium, evidence has now been provided that phosphate is crucial for the intraluminal binding of bile acids in complexes of calcium, phosphate, and bile acids. Supplemental calcium has been shown to reduce the cytotoxic potential of fecal water, which is probably attributable to the profound effect of calcium on bile acid and fatty acid metabolism. However, some reservation with regard to the protective ability of calcium seems to be warranted as we found that oral calcium supplementation caused an increase in epithelial proliferation rate in the sigmoid of patients with adenomatous polyps. Further controlled studies evaluating the effects of calcium on the epithelium of different parts of the colon should now be performed.