Exercise is a cornerstone in the management of type 2 diabetes because, over the short term, it can lower blood glucose levels. Regular exercise is also believed to improve insulin sensitivity and mitigate some of the increased cardiovascular risk associated with diabetes. However, studies examining the effect of exercise on glycemic control have yielded inconsistent results. Many have been too small to generate adequate statistical power. To better clarify the effect of exercise on glycemic control and body mass in people with type 2 diabetes, a group of Canadian researchers conducted a meta-analysis on the subject. Their findings appear in a recent Journal of the American Medical Association.

Study identification

The analysis was limited to controlled clinical studies (CCTs) using adult subjects with type 2 diabetes that included verification of compliance with the exercise plan through direct supervision or through exercise diaries. As glycosylated hemoglobin (HbA1c) was used as the main outcome of interest, only studies using an exercise intervention of 8 or more weeks and that had no drug component were included. A total of 14 studies (11 randomized and 3 non-randomized) were culled from nearly 1,500 identified CCTs. Two of them presented data for 2 comparison groups within the study, bringing the total number of comparisons to 16.

The shape of a typical exercise plan

The studies included a total of 504 participants evenly divided by gender, with a mean age of 55. In 12 studies that used aerobic training the mean [SD] frequency of exercise was 3.4 [0.9] times per week for 53 [17] minutes including 10 minutes of warm-up and cool-down. Most exercise plans centered on moderate aerobic activity such as walking or cycling. Two studies used progressively increased resistance training with a mean of 10 [0.7] exercises, with 2.5 [0.7] sets, and 13 [0.7] repetitions, 2.5 [0.4] times per week. On average, the exercise intervention lasted 18 weeks for aerobic programs and 15 weeks for the resistance training programs.

Exercisers see better results

The pooled HbA1c was significantly lower in the exercise groups compared with the control groups (7.65% vs 8.31%; weighted mean difference --0.66%; P<.001). The authors note that a similar reduction of 0.6% observed in a treatment group in the United Kingdom Prospective Diabetes Study was associated with a 32% reduction in diabetes-related clinical end points and a 42% reduction in diabetes-related deaths.

Exercise was not found to significantly reduce body mass. The researchers raise a number of potential explanations for this finding. These include the possibility that the exercise intervention was not lengthy or intensive enough for changes to be realized or that increases in physical activity resulted in increased lean body mass. Future research with longer intervention periods and better quantification of body composition changes would help clarify the relationship between exercise and body mass in this population.

Encouraging results

This analysis suggests that a relatively modest investment in physical activity can result in significant improvement in glycemic control. This is particularly heartening given the non-pharmacological nature of physical activity. These findings highlight the importance for health providers to encourage their patients with type 2 diabetes to undertake exercise programs.