Effect of Age on Systemic Delivery of Oral Glucose in Men

This study examined the effect of age on the posthepatic delivery of oral glucose (PHDG) during steady-state conditions. We used an intravenous-oral modification of the euglycemic insulin-clamp technique to assess PHDG in six men aged 24–39 yr (young) and eight men aged 65–83 yr (old). Each subject underwent two studies in which insulin was infused at 120 mU.m⁻² · min⁻¹ for 3 h, and either oral glucose (45 g) or water was given 60 min after initiating insulin. This level of insulin infusion is known to fully suppress hepatic glucose output. For each subject, PHDG was calculated as the difference between the whole-body glucose disposal rates in the paired studies. The time course of PHDG differed in the two groups (P < .0001), with an overall delay in PHDG in the older men. During the 1st h, younger men showed a greater PHDG (58.6 ± 3.8% of the oral load vs. 45.1 ± 4.2%) than the older group (P = .04). During the 2nd h, PHDG was less in the younger group (20.7 ± 4.9%) than the older group (36.6 ± 3.9%, P = .02). Over the 2-h period, total PHDG was comparable in younger (79.3 ± 7.4%) and older (81.7 ± 7.9%) men. These results indicate that normal aging is associated with significantly delayed but overall equal PHDG in men, consistent with the greater effect of age on 2-h rather than earlier postprandial glucose levels. It reinforces the role of impaired peripheral utilization as the primary mechanism of the glucose intolerance of aging.