Both aerobic and resistance types of exercise have been shown to be associated with a decreased risk of type 2 diabetes.9,10,45–48 In a large prospective study,46 each increase of 500 kcal (2100 kJ) in energy expenditure per week was associated with a decreased incidence of type 2 diabetes of 6% (relative risk 0.94, 95% CI –0.90 to 0.98)).
This benefit was particularly evident among people at high risk of diabetes (i.e., those with a high body mass index), a finding that has been supported by several other investigators.47,49 For instance, among 21 271 male physicians, those who reported weekly physical activity sufficient to cause a sweat had a reduced incidence of type 2 diabetes.47 Moderately intense levels of physical activity (5.5 Mets for at least 40 minutes per week) and of cardiovascular fitness (> 31 mL oxygen per kilogram per minute) have also been shown to be protective against the development of type 2 diabetes in middle-aged men,48 with an even greater effect among those at high risk of diabetes. Several investigators have reported a reduced incidence of type 2 diabetes among high-risk people (e.g., those who are overweight) after lifestyle interventions.50,51 A review of RCTs on the topic52 concluded that modest weight loss through diet and exercise reduced the incidence of the disease among high-risk people by about 40%–60% over 3–4 years. In one of the RCTs,53 a lifestyle intervention that included moderate physical activity for at least 150 minutes per week was found to be more effective than metformin alone in reducing the incidence of diabetes. It showed that only 7 people would need to be “treated” with the lifestyle intervention to prevent a single case of diabetes over a 3- year period, compared with 14 people given metformin.53 In summary, increasing research supports the importance of regular physical activity for the primary prevention of type 2 diabetes. Further research is warranted to uncover the ideal methods (e.g., resistance v. aerobic training) and intensity levels of exercise.
Exercise interventions are also effective in the management of diabetes. One prospective cohort study showed that walking at least 2 hours per week was associated with a reduction in the incidence of premature death of 39%–54% from any cause and of 34%–53% from cardiovascular disease among patients with diabetes.49 Moreover, walking that led to moderate increases in heart and breathing rates were associated with significant reductions in all-cause mortality (hazard rate ratio 0.57, 95% CI 0.41 to 0.80) and cardiovascular-related mortality (hazard rate ratio 0.69, 95% CI 0.43 to 1.09).49 In another cohort study,54 physically inactive men with established type 2 diabetes had a 1.7-fold increased risk of premature death compared with physically active men with type 2 diabetes.
This difference has also been observed among people with metabolic syndrome.55 Several clinical trials have been conducted on the topic.56–63 Both aerobic and resistance training has been shown to be of benefit for the control of diabetes; however, resistance training may have greater benefits for glycemic control than aerobic training may have.58 A meta-analysis of 14 controlled trials (11 randomized) revealed that exercise interventions resulted in a small but clinically and statistically significant reduction in glycosylated hemoglobin (0.66%) compared with no exercise intervention; 64 in most of the trials, participants in both the exercise and control groups were treated concurrently with oral hypoglycemic agents. This level of change is similar to that observed in studies comparing intensive glucose-lowering therapy with conventional treatments, a change that is known to be associated with a 42% reduction in diabetes-related mortality.64 In summary, exercise interventions for patients with diabetes are beneficial in improving glucose homeostasis. Prospective studies with an adequate follow-up show a strong association between exercise and reduced rates of death from any cause and from diabetes in particular. Future research will need to concentrate on examining the effects of dose (intensity and frequency of exercise).