The findings of the randomized, 26-week controlled trial, which was carried out in 8 community based centres all over Canada, are published in the September 18th, 2007 issue of the Annals of Internal Medicine.
The study was conducted by lead author Dr Ronald Sigal, associate professor of medicine and cardiac sciences at University of Calgary, Alberta, Canada, and colleagues.
Sigal said scientists already knew something about the benefit of exercise on blood sugar levels:
"We know that aerobic exercise improves glycemic control."
But what was less clear, said Sigal, was the effect of other types of exercise, particular resistance exercise, involving the lifting of weights to build strength:
" Some thought that resistance exercise is not useful or even dangerous for some people with diabetes," he explained.
Sigal and colleagues enrolled 251 sedentary adults with type 2 diabetes, aged 39 to 70 who were not taking regular exercise. They had to pass a stress test or be cleared for exercise training by a cardiologist though, and show they could stick to a 4 week exercise programme before being enrolled in the trial.
The participants were randomly assigned to one of four groups:
One group did 45 minutes of aerobic training, on treadmills and exercise bikes, three times a week (aerobics group).
A second group did 45 minutes of resistance training, on weights, three times a week (resistance group).
A third group did 45 minutes of aerobics and 45 minutes of resistance training three times a week (combined aerobics and resistance group).
A fourth group did no exercise (control group).
The researchers measured changes in participants' hemoglobin A1c value at 6 months and they also measured changes in body composition, plama lipid levels and blood pressure.
A1c reflects changes in blood sugar over the previous two to three months and is expressed as a percentage. An absolute drop of 1.0 per cent in A1c (for instance from 8.5 to 7.5 per cent) reflects a 15 to 20 per cent reduction in heart attack and stroke risk, and a 25 to 40 reduction in risk of diabetes-related eye or kidney disease.
The results showed that:
- A1c in the aerobics group (compared to control) dropped by 0.51 per cent.
- In the resistance group it dropped by 38 per cent.
- However, the combined aerobics and exercise group showed a drop in A1c of 46 per cent over the aerobics only group and 59 per cent over the resistance only group.
- This meant an overall drop of 97 per cent in A1c value in the combined exercise group compared to the no exercise group.
- The no exercise (control) group showed no change in A1c value after 6 months.
- Changes in blood pressure and lipid levels did not differ significantly among the groups.
- Adverse events were more common in the three exercise groups than in the control group.
" Either aerobic or resistance training alone improves glycemic control in type 2 diabetes, but the improvements are greatest with combined aerobic and resistance training."
Dr Sigal said that of those participants who already had good blood sugar control at the start of the study, the ones who did both aerobics and resistance training demonstrated further improvement in glucose control.
"The bottom line," said Sigal, "is that doing both aerobic and resistance exercise is the way to maximize the effects of exercise on blood glucose control in type 2 diabetes".
In an accompanying editorial, Drs William E Kraus and Benjamin D Levine wrote:
"Imagine an inexpensive pill that could decrease the hemoglobin A1c value by 1 percentage point, reduce cardiovascular death by 25 percent, and substantially improve functional capacity (strength, endurance, and bone density)."
"Diabetes experts would be quick to incorporate this pill into practice guidelines and performance measures for diabetes," they added.
They suggested these results should encourage all clinicians to include exercise advice and counselling as part of treatment for type 2 diabetes.
In reflecting on the study's limitations the authors said that the results could not be generalized to patients who do not stick to exercise programmes, since those participants were excluded from the study. Also, they pointed out that:
"The participants were not blinded, and the total duration of exercise was greater in the combined exercise training group than in the aerobic and resistance training groups," implying that increased exercise duration could have something to do with the added improvement observed in the combined exercise group.
The World Health Organization (WHO) estimates that worldwide there are nearly 200 million people with diabetes, mostly type 2, and this number will be 300 million in 2025.
Risk for type 2 diabetes is strongly linked with genes, but lifestyle factors such as lack of exercise and diet are also important contributors.
"Effects of Aerobic Training, Resistance Training, or Both on Glycemic Control in Type 2 Diabetes: A Randomized Trial."
R. J. Sigal, G. P. Kenny, N. G. Boulé, G. A. Wells, D. Prud'homme, M. Fortier, R. D. Reid, H. Tulloch, D. Coyle, P. Phillips, A. Jennings and J. Jaffey.
Ann Intern Med 2007; 357-369.
Published online 18th September 2007.
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