Structured Exercise Controls Blood Sugar

In their background information, Daniel Umpierre, M.Sc., of the Hospital de Clinicas de Porto Alegre, Brazil, and colleagues, discussed how exercise has become a "cornerstone" of the management of diabetes, sitting alongside dietary changes and medication. Current guidelines recommend that patients undertake a total of at least 150 minutes of moderate-intensity aerobic exercise on at least three occasions a week. However, while this is backed by a lot of research, it is not clear what type of exercise helps the most, and whether doing more of it makes a difference.

So they carried out a systematic statistical review of all the published randomized controlled trials they could find that examined the effect of structured exercise training (aerobic, resistance, or both) or physical activity advice (with and without dietary advice) with reductions in hemoglobin A1c (HbA1c), a marker of glucose control, in patients with Type 2 diabetes.

They decided only to include studies that ran for at least 12 weeks, and where the "treated" patients were compared to a control group that did not follow the intervention, and where the researchers took before and after measures of HbA1c levels.

After searching MEDLINE, Cochrane-CENTRAL, EMBASE, and other established registries and records of clinical trials, published between January 1980 and February 2011, they found over 4,000 articles about this type of research, of which 47 were randomly controlled trials that met their criteria: altogether these covered 8,538 participants, including controls.

From the 23 studies that covered structured exercise training, Umpierre and colleagues found that overall, undertaking this type of exercise, such as following a program at a gym or with a personal instructor, was associated with a 0.67% reduction in HbA1c level compared with controls.

They also found, when they looked specifically at structured aerobic training (the sort of exercise that makes you breathless and sweaty, like jogging, fast pace walking, cycling, and aerobics classes) the reduction in HbA1c was bigger, at 0.73%.

Structured resistance training (for instance using weights to develop strength) also seemed to have an effect (this was associated with 0.57% reduction in HbA1c), although not as dramatic as structured aerobic training.

The researchers also found that doing more than 150 minutes a week of structured exercise appears to increase the benefit, up to 0.89% reduction in HbA1c levels, they found. In contrast, doing less than 150 minutes a week, on average was linked to a much lower 0.36% reduction.

Twenty-four of the studies looked at the effect of giving advice about physical exercise. Their data showed that overall this was associated with a 0.45% reduction in HbA1c, but closer examination revealed that while a 0.58% reduction was linked to interventions that combined physical activity advice with dietary advice, "physical activity advice alone was not associated with HbA1c changes," wrote the researchers.

Umpierre and colleagues concluded that their findings show structured aerobic, resistance, and combined training are each linked to similar reductions in HbA1c in patients with Type 2 diabetes, and that doing more than 150 minutes a week of such exercise is linked to greater reductions than doing less. However, they could not find any apparent benefit from doing more intensive exercise:

"Although high-intensity exercise has been previously shown to have an association with HbA1c reduction, our findings did not demonstrate that more intensive exercise was associated with greater declines in HbA1c," wrote the researchers.

In conclusion they found that structured exercise training that consists of aerobic exercise, resistance training, or both combined is associated with HbA_1c reduction in patients with Type 2 diabetes. Structured exercise training of more than 150 minutes per week is associated with greater HbA_1c declines than that of 150 minutes or less per week. Physical activity advice is associated with lower HbA_1c, but only when combined with dietary advice. 

JAMA. 2011;305 (17):1790-1799