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QUESTION: In patients with type 2 diabetes mellitus, does exercise training improve glycaemic control (reduce glycosylated haemoglobin [HbA1c] concentrations) and reduce body mass?
Data sources
Studies in all languages were identified by searching Medline (1966 to 2000), EMBASE/Excerpta Medica (1980 to 2000), Sport Discuss (1949 to 2000), HealthSTAR (1975 to 2000), Dissertation Abstracts (1861 to 2000), and the Cochrane Controlled Trials Register; by checking the reference lists of major textbooks, review articles, and relevant articles from the search; and by contacting experts.
Study selection
Studies were selected if they were randomised controlled trials (RCTs) or controlled clinical trials (CCTs) of exercise interventions lasting ≥ 8 weeks in patients with type 2 diabetes in whom compliance could be verified by direct supervision or diaries.
Data extraction
2 investigators independently extracted data on sample size, baseline, and post-treatment means and standard deviations of the intervention and control groups for HbA1c concentrations and body mass, exercise programme characteristics (type, frequency, duration, intensity, and energy cost), and study quality (randomisation, blinding, withdrawals, and concealment).
Main results
14 trials (11 RCTs) were included (504 patients, mean age 55 y, 50% men, mean duration of diabetes 4.6 y). The duration of the intervention ranged from 8 to 52 weeks (mean 18 wks). Study quality was moderate to low (mean score 1.6 out of 5 points). 12 trials that compared exercise with no exercise showed reduced HbA1c concentrations with the exercise programme (p < 0.001) (table). 2 trials that compared diet plus exercise with no diet and no exercise also showed reduced HbA1c concentrations with the intervention (p=0.008) (table). A sensitivity analysis showed no difference between results from RCTs and CCTs (table). The results did not differ by type of exercise (aerobic v resistance training). Exercise alone (12 trials, p=0.60) or combined with diet (2 trials, p=0.24) did not reduce body mass (table). The results did not differ when RCTs, CCTs, aerobic training, or resistance training were analysed separately. Meta-regression analysis showed that the reduction in HbA1c concentrations could not be predicted by change in body mass, exercise intensity, or total amount of exercise.
Conclusion
In patients with type 2 diabetes mellitus, exercise training reduces HbA1c concentrations but does not reduce body mass.
Exercise v no exercise for type 2 diabetes at mean 18 weeks*
QUESTION: In patients with type 2 diabetes mellitus, does exercise training improve glycaemic control (reduce glycosylated haemoglobin [HbA1c] concentrations) and reduce body mass?
Commentary
Exercise is widely recommended to patients with type 2 diabetes mellitus; however, evidence for its effect on glycaemic control is scarce. Although patients enrolled in exercise programmes obviously increase their energy output, they may compensate by spending less energy in other daily activities — a decrease in energy expenditure that is rarely accounted for in most studies.1,2
Without adjustment for overall energy expenditure and other factors associated with exercise, it is difficult to predict the independent effect of exercise interventions on body mass and glycaemia, which also makes it difficult to provide specific recommendations to patients and practitioners. Any increase in energy expenditure will improve glucose tolerance. The meta-analysis by Boulé et al shows that three 45 minute moderate intensity aerobic workouts per week (similar to the activity goals specified in the clinical guidelines for the treatment of obesity3) can reduce HbA1c concentrations to a degree sufficient to reduce risk for myocardial infarction by 9% and microvascular complications by 24%, according to UK Prospective Diabetes Study Group data.4
Many patients with diabetes do not have access to supervised exercise programmes. Even among those who do have access, simple lifestyle changes (eg, brisk walking daily) is more likely than supervised exercise to be sustained over the long term.5 This study does not address how to help patients sustain increased physical activity — a major challenge facing physicians and their patients with type 2 diabetes.
Footnotes
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Sources of funding: Natural Sciences and Engineering Research Council of Canada; Ontario Ministry of Health and Long Term Care; Canadian Institutes of Health Research.
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For correspondence: Dr R J Sigal, Ottawa Health Research Institute, Ottawa, Ontario, Canada. rsigal@ohri.ca.