Bacterial transformation of bile acids is possibly involved in colorectal carcinogenesis. In several epidemiological studies, the secondary bile acid concentration in feces is related to the incidence of colonic cancer. However, data on fecal bile acids in case-control studies are conflicting. We investigated the influence of age, intestinal transit time, and dietary composition on fecal bile acid profiles in healthy subjects of three different age groups (mean ages 22, 48, and 67 years). Fecal bile acids were analyzed by gas-liquid chromatography. The concentration of the major secondary fecal bile acids increased with advancing age and was significantly higher in elderly subjects, compared to young adults. The concentration in middle-aged persons was intermediate. Analysis of dietary constituents showed that the fat intake in the three groups was comparable. The dietary fiber intake in elderly subjects was significantly lower than in the other two groups. The former group did excrete less dry fecal material compared to both other groups. Dietary fiber intake was negatively correlated with the total bile acid concentration. Probably, a decrease in dietary fiber intake results in higher fecal bile acid concentrations with advancing age. From the findings of this study, it is obvious that matching for age is important when case-control studies concerning the role of fecal bile acids in colorectal carcinogenesis are conducted.

It has been suggested that transformation of secondary bile acids into (co)carcinogenic compounds may have a role in the development of cancer of the large bowel. Because of age dependent differences of this disease we undertook a study of cholic and deoxycholic acid metabolism of eleven young adults (group A, 20-30 years old) and eleven elderly persons (group B, 55-75 years old) with a double isotope dilution method. Daily food intake was standardized individually and gut transit time measured with radioopaque pellets and labelled chromium chloride. The 7 alpha-dehydroxylation fractions (the ratio of deoxycholic acid input rate from the large bowel to cholic acid synthesis rate) were higher in group B (P less than 0.01) due to higher deoxycholic acid input rates (P less than 0.005), especially when individuals from both groups with rapid gut transit were compared. As contributory factor was recognized the higher fractional turnover rate of cholic acid in group B. Pool sizes and synthesis rates of cholic acid and gut transit times were similar. In group A, but not in B, gut transit times correlated with deoxycholic acid input rates (P less than 0.01). The differences in bile acid metabolism may be related to a more effective colonic absorption of deoxycholic acid in the elderly persons with a concomitant decrease of active ileal absorption of cholic acid in the elderly persons. Differences in diet or gut transit time between both groups do not seem to be the underlying mechanism.