Effect of age on tests of intestinal and hepatic function in healthy humans.

We studied intestinal function and hepatic microsomal phase I monooxygenase function in healthy, free-living subjects, aged 19-91 yr. In subjects (n = 114) given a diet including 100 g/day of fat, fecal fat in a 72-h collection did not increase with advancing age. D-Xylose excretion (n = 54) following a 25-g oral load significantly declined with increasing age, but a concomitant decline in creatinine clearance suggested a decrease in renal function rather than an absorptive defect. Furthermore, there was no evidence for an age-associated increase in bile salt deconjugation by intestinal bacteria as shown by the glycocholate breath test (n = 60). Finally, there was no evidence for a decrease in hepatic microsomal function with advancing age as measured by the aminopyrine breath test (n = 60). We conclude that digestive/absorptive and hepatic microsomal phase I monooxygenase function are well preserved in healthy humans throughout life.