The effect of age on plasma proinsulin-like material after oral glucose

The total plasma insulin and proinsulin-like material after oral glucose was studied in 68 lean subjects of varying ages with normal glucose tolerance tests. Although each subject had a normal test, the mean glucose levels increased with increasing age. When younger subjects (ages 15 to 44) were compared with older (45 to 74), no significant differences in total insulin responses were seen, but plasma proinsulin-like material was significantly higher in the older age subjects. All values after stimulation were significantly greater in subjects 45 to 74 years of age than in those 15 to 44 years of age (p less than 0.01). A significant correlation between the amount of proinsulin and the age of the subject was seen. These findings may reflect a decreased conversion of proinsulin to insulin in the aging pancreas or could reflect decreased clearance of proinsulin in older subjects.