Effect of age on intestinal absorption of riboflavin in humans

The development of gastrointestinal absorption function in humans was studied using riboflavin, a vitamin which is absorbed by a site‐specific (proximal small intestine) and saturable transport process. Oral doses of 150 mg./m.² body surface area of riboflavin‐5′‐phosphate were administered in solution to subjects ranging in age from 0.25 to 40 years. The urinary recovery of the vitamin increased significantly (from 6 to 12% of the dose) over this age range. The ratio of maximum excretion rate to dose and the time of occurrence of the maximum excretion rate were independent of age. The kinetics of riboflavin elimination also did not show any appreciable change with age. These observations suggest that, in the age range studied, younger subjects retain the vitamin at intestinal absorption sites for a shorter period of time than do older subjects. This appears to be due to decreased intestinal transit rate with increasing age. Prompt release of drugs from pharmaceutical dosage forms seems therefore even more important in children than in adults in order to assure adequate absorption.