Dairy foods and prevention of colon cancer: human studies.

Colon cancer is the commonest gastrointestinal cancer and the second leading cause of cancer deaths in the United States. Recent approaches to lowering the incidence of colon cancer have included attempts at dietary prevention and chemoprevention. International and national incidence rates for colon cancer suggest an inverse relationship with dietary calcium and/or vitamin D intake (or sun exposure). Several human intervention studies have suggested that supplemental calcium administration will change proliferative indices of risk for colon cancer from high to lower risk patterns. The principal current hypothesis for the action of calcium implies that calcium may precipitate or bring out of solution fatty acids and bile acids that are potentially toxic to the colorectal epithelium. Both calcium administration and dairy food administration are associated with lowering aqueous fecal concentrations of bile acids and fatty acids accompanied by a highly significant lowering of cytotoxicity in studies in vitro. There is biochemical and biological evidence in cell culture systems that exposure to calcium and/or vitamin D reduces the oncogenic properties of colon cancer cells. A recent blinded study of the administration of low-fat dairy foods demonstrated a significant improvement in several parameters of proliferation as well as in two differentiation markers from a high to a lower risk pattern. Furthermore, administration of calcium also has been shown to reduce the incidence of recurrent adenomatous polyps in individuals at increased risk for colon polyp formation because of the presence of prior colon adenomata. These combined data suggest that administration of supplemental calcium or low-fat dairy foods may have a significant effect upon colonic polyp and perhaps colon cancer incidence.