Effects of Exercise Training Intensity on Pancreatic β-Cell Function
Diabetes Care
vol. 32, 1807 - 1811, 2009
Abstract
Objective:
Insulin resistance and β-cell dysfunction both are important contributors to the pathogenesis of type 2 diabetes. Exercise training improves insulin sensitivity, but its effects on β-cell function are less well studied.
Research Design and Methods:
Sedentary, overweight adults were randomized to control or one of three 8-month exercise programs: 1) low amount/moderate intensity, 2) low amount/vigorous intensity, or 3) high amount/vigorous intensity. Of 387 randomized, 260 completed the study and 237 had complete data. Insulin sensitivity (Si), acute insulin response to glucose (AIRg), and the disposition index (DI=Si×AIRg) were modeled from an intravenous glucose tolerance test.
Results:
Compared with control subjects, all three training programs led to increases in DI. However, the moderate-intensity group experienced a significantly larger increase in DI than either of the vigorous-intensity groups and through a different mechanism. The high-amount/vigorous-intensity group improved Si and had a compensatory reduction in AIRg, whereas the moderate-intensity group had a similar improvement in Si but almost no reduction in AIRg. Importantly, the inactive control group experienced a significant increase in fasting glucose.
Conclusions:
To the extent that the DI accurately reflects β-cell function, we observed that both moderate- and vigorous-intensity exercise training improved β-cell function, albeit through distinct mechanisms. It is not clear which of these mechanisms is preferable for maintenance of metabolic health. While moderate-intensity exercise led to a larger improvement in DI, which may reflect a transition toward a more normal DI, longer-term investigations would be necessary to determine which was more effective at reducing diabetes risk.
Commentary
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Articles that have been selected because they must be read in order to provide safe current medical practice.
A: Evidence from an article that is shown in a human (double-blind, when appropriate), randomized trial, meta-analysis or both
The epidemic of type-2 diabetes mellitus appears to reflect both a decrease in sensitivity to insulin and a malfunction of the pancreatic β-cells.1-3 As insulin sensitivity falls in the obese person there is a compensatory hyperactivity of the β-cells until these eventually fail.4,5 The disposal index, used in this study, is a measure of the individual's capacity to respond to a loss of insulin sensitivity. The volume and intensity of the 3 exercise regimens chosen for the present 8-month experiment reflect the treatment of obese subjects; the high intensity, high volume program was at 65% to 80% of peak oxygen intake, but corresponded to no more than 32km of walking or jogging per week, a normal exercise routine for many active elderly people, and perhaps for this reason program adherence (67%) was relatively good. Somewhat surprisingly, although all 3 exercise groups tended to improve, the largest increase in the index of β-cell function was seen with the moderate intensity low volume group (Fig 1 in the original article). The authors caution that further, longer duration studies are needed to confirm that the moderate intensity low volume program has the greatest effect in reducing the risk of developing diabetes. The findings are puzzling, as traditional markers of success such as reductions in obesity were greater in the subjects taking more physical activity. One possible factor contributing to differences in response is that a greater proportions of fat is metabolized with lower intensity exercise, with less of a resultant tendency to lipotoxicity in the pancreas.6
