Age-dependent alterations of intestinal absorption. II. A clinical study using a modified D-xylose absorption test.

With advancing age functional and morphological changes take place within the intestinal tract. The age-dependency of intestinal absorption has been studied using a D-xylose absorption test. The absorption rate (constant k12), the time of appearance of the relative maximum of the D-xylose concentrations in the blood serum after oral administration (time tm), and the extent of the relative absorption in the small intestine as a function of time RA(t) were determined by graphic-mathematical evaluation of the blood level kinetics of D-xylose after oral and intravenous administration. Within the age range of 3 to 96 yr, it has been proven that a slowing down of intestinal absorption occurs with advancing age. By prolonging the period during which the food components are absorbed in the small intestine (shift of tm towards the absorption processes take place at a slower rate. Absorption disorders in old age are due to morbidity and not, sui generis, to involution.