Exercise, dietary changes and medications are frequently used in the management of type 2 diabetes. However, it is difficult to determine the independent effect of exercise from some trials because exercise has been combined with dietary modifications or medications, or compared with a control which includes another form of intervention. The review authors aimed to determine the effect of exercise on blood sugar control in type 2 diabetes.
This review found that exercise improves blood sugar control and that this effect is evident even without weight loss. Furthermore, exercise decreases body fat content, thus the failure to lose weight with exercise programmes is probably explained by the conversion of fat to muscle. Exercise improved the body's reaction to insulin and decreased blood lipids. Quality of life was only assessed in one study, which found no difference between the two groups. No significant difference was found between groups in blood levels of cholesterol or blood pressure. A total of 14 randomised controlled trials were assessed. These included 377 participants and compared groups that differed only with respect to an exercise programme intervention. The duration of the interventions in the studies ranged from eight weeks to one year. Two studies reported follow-up information, one at six months after the end of the six month exercise intervention and one at twelve months post-intervention. Generally, the studies were well-conducted, but blinding of outcome assessors was not reported and although all studies reported that randomisation was performed, few gave details of the method.
No adverse effects with exercise were reported. The effect of exercise on diabetic complications was not assessed in any of the studies.
The relatively short duration of trials prevented the reporting of any significant long term complications or mortality. Another limitation was the small number of participants included in the analyses for adiposity, blood pressure, cholesterol, body's muscle and quality of life.
The meta-analysis shows that exercise significantly improves glycaemic control and reduces visceral adipose tissue and plasma triglycerides, but not plasma cholesterol, in people with type 2 diabetes, even without weight loss.
Exercise is generally recommended for people with type 2 diabetes mellitus. However, some studies evaluate an exercise intervention including diet or behaviour modification or both, and the effects of diet and exercise are not differentiated. Some exercise studies involve low participant numbers, lacking power to show significant differences which may appear in larger trials.
To assess the effects of exercise in type 2 diabetes mellitus.
Trials were identified through the Cochrane Central Register of Controlled Trials (CENTRAL), MEDLINE, EMBASE and manual searches of bibliographies.
All randomised controlled trials comparing any type of well-documented aerobic, fitness or progressive resistance training exercise with no exercise in people with type 2 diabetes mellitus.
Two authors independently selected trials, assessed trial quality and extracted data. Study authors were contacted for additional information. Any information on adverse effects was collected from the trials.
Fourteen randomised controlled trials comparing exercise against no exercise in type 2 diabetes were identified involving 377 participants. Trials ranged from eight weeks to twelve months duration. Compared with the control, the exercise intervention significantly improved glycaemic control as indicated by a decrease in glycated haemoglobin levels of 0.6% (-0.6 % HbA1c, 95% confidence interval (CI) -0.9 to -0.3; P < 0.05). This result is both statistically and clinically significant. There was no significant difference between groups in whole body mass, probably due to an increase in fat free mass (muscle) with exercise, as reported in one trial (6.3 kg, 95% CI 0.0 to 12.6). There was a reduction in visceral adipose tissue with exercise (-45.5 cm2, 95% CI -63.8 to -27.3), and subcutaneous adipose tissue also decreased. No study reported adverse effects in the exercise group or diabetic complications. The exercise intervention significantly increased insulin response (131 AUC, 95% CI 20 to 242) (one trial), and decreased plasma triglycerides (-0.25 mmol/L, 95% CI -0.48 to -0.02). No significant difference was found between groups in quality of life (one trial), plasma cholesterol or blood pressure.