Short-term exercise improves β-cell function and insulin resistance in older people with impaired glucose tolerance

Background: There is a high prevalence of diabetes and impaired glucose tolerance (IGT) in the older population. Normal aging is associated with insulin resistance and impaired insulin secretion, with greater defects in people with IGT. Short-term exercise has been found to increase insulin sensitivity, but little is known about acute exercise effects on p-cell function in older people with IGT. Methods: We assessed the effects of 7 consecutive days of supervised aerobic exercise (1 h/d at 60-70% heart rate reserve) in 12 sedentary older people with IGT. Screening included oral glucose tolerance test, stress/maximal O-2 uptake test, and dual-energy x-ray absorptiometry scan. Participants had a frequently sampled iv glucose tolerance test at baseline and 15-20 h after the seventh exercise session. Insulin sensitivity (S-1), glucose disappearance constant (Kg, a measure of iv glucose tolerance), acute insulin response to glucose (AIRg), and disposition index (AIRg x S-1), a measure of beta-cell function in relation to insulin resistance, were calculated. Results: Exercise was well tolerated. Body weight, fasting glucose, fasting insulin, and iv glucose tolerance were unchanged with exercise. S, increased by 59%, AIRg decreased by 12%, and disposition index increased by 31%. There was no significant change in fasting lipid, catecholamine, leptin, or adiponectin levels. Conclusions: Short-term exercise not only improved insulin resistance but also significantly enhanced p-cell function in older people with IGT. These effects of short-term exercise on beta-cell function cannot be explained by changes in body weight or circulating levels of lipids, leptin, adiponectin, or catecholamines.