Studies of calcium in food supplements in humans.

Colon cancer is one of the commonest cancers in the Western world. Environmental factors appear to predominate as exemplified by a change in incidence in colon cancer within 20 years when people emigrate from a low- to a high-incidence country. It had been suggested that a diet high in energy, fat, and meat content and low in fiber content is most likely responsible. Epidemiologic observations have pointed to a potential effect of calcium or/and vitamin D in reducing the incidence of colon cancer. Other studies have shown a reduction in preneoplastic colon adenomas with increased calcium or/and vitamin D intake. High fat diets were shown to be accompanied by an increase in fecal fatty acids and bile acids or a change in bile acid composition. Soluble fatty acids and bile acids then could interact with the colonic epithelium inducing cell damage and increased proliferation. A hypothesis was developed suggesting that calcium supplementation and increased calcium in the colonic lumen would precipitate these bile acids and fatty acids. Examination of the effect of supplemental calcium or calcium in dairy foods showed a major reduction in fecal bile acids and fatty acids in solution in volunteers and accompanied by a reduction in cytolytic activity. Studies then were performed in patients at risk for colon cancer seeking a change in proliferative biomarkers of risk from a high-risk to a low-risk pattern with supplemental calcium administration. These studies generally have shown a beneficial effect of the addition of calcium at 1.2-2 gm per day in addition to a regular diet for periods of 2 to 6 months. A recently published study also demonstrated that a diet, in which low-fat dairy foods containing an average of about 825 mg of calcium, significantly improved proliferative biomarkers as well as two differentiation bio-markers of risk for colon cancer from a high- to a low-risk pattern. These observations, together with recent studies showing reduced adenomatous polyp recurrence when supplemental calcium was provided, demonstrate the potential of calcium and perhaps vitamin D as chemopreventive agents for colorectal neoplasia.