Randomized trial of the effect of calcium supplementation on fecal risk factors for colorectal cancer.

Newmark et al. (J Natl Cancer Inst 1984; 72:1323-8) hypothesized that supplementation with calcium would decrease the concentration of bile acids in aqueous phase feces and that such a reduction would reduce the risk of malignant disease in the bowel. A randomized trial was therefore undertaken to examine the effects of calcium supplementation on fecal biochemistry. A total of 68 men between 40 and 60 years of age volunteered to participate after having been selected randomly from population lists in Scarborough, a city in the Toronto area, Ontario, Canada. Participants were randomly assigned to receive a daily supplement of 3 g of calcium carbonate or a sucrose placebo for a period of 1 week. Fecal samples were collected for 2 days prior to supplementation and for the last 2 days of supplementation. Records of all foods consumed were kept throughout the study period. The average concentration of total soluble bile acids fell in the placebo group (-11.2 g/ml) but increased slightly in the calcium group (1.4 g/ml). Similar patterns of change were observed for deoxycholic acid (placebo, -3.0 g/ml; calcium, 4.5 g/ml). The distribution of changes in total bile acids and deoxycholic acid differed between randomization groups at the 10 percent level of significance in univariate analysis. After adjustment for initial stool chemistry and initial levels and changes in nutrient intake, no reduction in fecal bile acid levels was observed in association with calcium supplementation. In fact, a statistically significant (p = 0.05) increase in deoxycholic acid concentration remained in the calcium supplemental group. Thus, this study was unable to support the hypothesis that calcium supplementation alters aqueous phase bile acids in the manner hypothesized to be consistent with protection from colorectal cancer.