Insulin action in aging man: evidence for tissue-specific differences at low physiologic insulin levels

This study examined the effect of age on insulin action in several tissues. Euglycemic insulin clamp studies were performed on healthy young (n = 7, 20 to 35 years, 10 and 20 mU/m2 X min insulin infusions) and old (n = 7, 66 to 80 years, 8 and 16 mU/m2 X min insulin infusions) adults. Insulin values were similar during both the lower (young, 24 +/- 1.6, old, 24 +/- 2.1 microU/ml) and higher (young, 40 +/- 3.3; old, 39 +/- 3.8 microU/ml) insulin infusion rates. Although suppression of hepatic glucose output (HGO) was more rapid (p less than .05) in the elderly group at each dose, HGO was eventually suppressed to similar levels in both age groups (low dose: young, 34.4 +/- 10.8, old, 25.3 +/- 1.8 mg/m2 X min; higher dose: young, 22.8 +/- 10.2, old, 6.2 +/- 2.1 mg/m2 X min). Glucose disposal was less (p less than .01) in the aged group at both insulin infusion rates. Suppression of C-peptide was slower in the elderly participants (p less than .05) in the low dose study. Suppression of free fatty acid and glucagon levels was the same in each age group. We concluded that the insulin resistance of aging is not generalized to all tissues.