Physical inactivity and obesity underlie the insulin resistance of aging

Abstract

OBJECTIVE Age-associated insulin resistance may underlie the higher prevalence of type 2 diabetes in older adults. We examined a corollary hypothesis that obesity and level of chronic physical inactivity are the true causes for this ostensible effect of aging on insulin resistance. RESEARCH DESIGN AND METHODS We compared insulin sensitivity in 7 younger endurance-trained athletes, 12 older athletes, 11 younger normal-weight subjects, 10 older normal-weight subjects, 15 younger obese subjects, and 15 older obese subjects using a glucose clamp. The nonathletes were sedentary. RESULTS Insulin sensitivity was not different in younger endurance-trained athletes versus older athletes, in younger normal-weight subjects versus older normal-weight subjects, or in younger obese subjects versus older obese subjects. Regardless of age, athletes were more insulin sensitive than normal-weight sedentary subjects, who in turn were more insulin sensitive than obese subjects. CONCLUSIONS Insulin resistance may not be characteristic of aging but rather associated with obesity and physical inactivity.

Figure 1

Insulin sensitivity in athletes and sedentary normal-weight and obese, young, and old individuals. Bars are mean rates of insulin-stimulated glucose disposal (R_d), and error bars are SEM. One-way ANOVA with Tukey-Kramer HS adjustment: *difference (P < 0.05) between athletes and either normal-weight or obese, **significant difference (P < 0.05) between normal weight and obese. □, younger; ■, older.