Factors affecting the absorption of riboflavin in man

The urinary recovery of riboflavin as a function of dose after oral administration to fasted normal humans shows that the process responsible for the absorption of this vitamin is saturable. The saturation effect is not evident when riboflavin doses as high as 30 mg. are administered after a meal. The enhanced absorption of riboflavin in the presence of food appears to be due to a decrease in intestinal transit rate which causes the vitamin to be retained at absorption sites in the small intestine for a longer period of time. The site specificity and saturability of riboflavin absorption suggest that the vitamin is absorbed by specialized transport rather than by passive diffusion. This conclusion is supported by kinetic and physical‐chemical data, as well as by the results of studies of the effect of route of administration on the recovery of riboflavin in the urine.