Physical Inactivity and Obesity Underlie the Insulin Resistance of Aging

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.