Prevention of T2DM: Physical exercise
Type 2 diabetes can be prevented or at least postponed by physical activity and a healthy diet. In the last decade, associations between physical activity and changes in physical activity levels with the risk of type 2 diabetes have been evaluated by a number of prospective studies and clinical trials. The results based on these prospective studies and clinical trials have shown that moderate to high levels of physical activity and an increase in physical activity levels can prevent type 2 diabetes. Thus, there is consistent evidence that 30 minutes of moderate intensity aerobic physical for at least 5 days a week reduces the risk of type 2 diabetes. This is broadly consistent with the current recommendations for physical activity in adults. More recently, it has been shown that weight training or aerobic exercise for at least 150 minutes per week are both independently associated with a lower risk of type 2 diabetes, and that the combination of both forms of exercise is associated with greater reduction risk of type 2 diabetes.
Mechanisms of physical activity in the prevention of type 2 diabetes mellitus
The large body of literature demonstrates that regular physical activity can improve insulin sensitivity and other components of the metabolic syndrome, e.g. decrease blood pressure, increase plasma levels of high-density lipoprotein cholesterol, decrease plasma levels of triglycerides, reduce body weight and maintain healthy weight, and also reduce the risk of developing the metabolic syndrome. The analysis from the Insulin Resistance Atherosclerosis Study showed that both vigorous and non-vigorous activities were associated with higher insulin sensitivity among 1467 men and women of 40 to 69 years of age. The British Regional Heart Study examined the role of serum insulin concentration and components of the insulin resistance syndrome in the relation between physical activity and the incidence of type 2 diabetes among 5159 men of 40 to 59 years of age. It showed that physical activity was significantly and inversely associated with serum insulin concentrations and many components of the metabolic syndrome, and serum insulin concentrations and the components of the metabolic syndrome was a mediating factor in the relation between physical activity and the incidence of type 2 diabetes.
Evidence of cohort studies
An amateur tennis player, currently injuredMore than twenty prospective epidemiological studies of physical activity and the risk of type 2 diabetes have been published and they have clearly shown the benefit of physical activity in the prevention of type 2 diabetes. The early landmark study conducted in 5990 male alumni of the University of Pennsylvania investigating the association between leisure time physical activity and the risk of type 2 diabetes showed that leisure time physical activity was effective in the prevention of type 2 diabetes. Later, the Nurses´ Health Study involving 87 253 US women reported that women who were engaged in vigorous exercise at least once per week had a 33% reduced aged-adjusted relative risk of type 2 diabetes compared with women who did not exercise weekly after a 8 years of follow-up. Studies carried out in other parts of the world revealed similar results. The Osaka Health Survey for instance included 6013 Japanese men aged 35-60 years who were free of diabetes, impaired fasting glycemia, or hypertension at baseline. Men who participated in regular physical exercise at least once a week and vigorous activity only once a week at weekends were associated with a decreased risk of type 2 diabetes. A large Finnish cohort study consisting of 6898 Finnish men and 7392 women of 35 to 64 years of age without a history of stroke, coronary heart disease, or diabetes at baseline reported that moderately active work was associated with a 30% reduction in the risk of type 2 diabetes and that moderate leisure-time physical activity was related to a 19% decrease in the risk of type 2 diabetes compared to the most sedentary group during a follow-up of 12 years. Daily walking or cycling to and from work for more than 30 minutes was also significantly and inversely associated with the risk of type 2 diabetes.
Evidence of clinical trials
First clinical trials conducted in Sweden and China regarding changes in physical activity in the prevention of type 2 diabetes demonstrated that changes in lifestyle that included physical activity can prevent type 2 diabetes. The Malmö study from Sweden used increased physical exercise and weight loss as major intervention strategies to prevent and delay type 2 diabetes. Participants with impaired glucose tolerance had less than half the risk of developing type 2 diabetes compared to those who did not take part in the exercise program during the 5-year follow-up. In the Da Qing study in China, 577 individuals with impaired glucose tolerance were divided into four groups (i) exercise alone; (ii) diet alone; (iii) diet plus exercise; and (iv) a control group. The cumulative incidence of type 2 diabetes during 6 years was significantly lower in the three intervention groups compared with the control group (41% in the exercise group, 44% in the diet group, 46% in the diet plus exercise group, and 68 % in the control group) and remained significant even after adjusting for differences in baseline body mass index and fasting glucose. A major limitation of these two studies, however, was that the study participants were not randomly assigned to the intervention and control groups.
These results were later confirmed by two well-designed randomized controlled trials in Finland and the United States. In the Finnish Diabetes Prevention Study (DPS), 522 middle-aged men and women with impaired glucose tolerance were randomized either to the intensive lifestyle intervention group consisting of nutritional and physical activity interventions or the control group. The physical activity intervention consisted of supervised, progressive, individually tailored circuit-type resistance training sessions with the goal to accumulate 30 minutes of physical activity/day. The cumulative incidence of diabetes after four years was 11% in the intervention group and 23% in the control group. During the entire trial, the risk of diabetes was reduced by 58% in the intervention group. The role of leisure time physical activity in preventing type 2 diabetes was evaluated by examining the association of the changes in leisure time physical activity during the study with the incidence of diabetes in the combined intervention and control groups. In the combined groups, an increase in total leisure time physical activity was associated with a lower diabetes incidence. Participants in the upper third of the change in total leisure time physical activity were 80% less likely to develop diabetes during the trial than those in the lower third. Participants who were in the upper third for a change in moderate-to vigorous leisure time physical activity were 49 to 65% less likely to develop diabetes than those who were in the lower third.
In the U.S. Diabetes Prevention Program (DPP), the 3234 non-diabetic persons with elevated fasting and post-load plasma glucose concentrations were randomized into placebo, metformin, or a lifestyle-modification program with the goals of at least a 7% weight loss and at least 150 minutes of physical activity per week. The exercise intervention emphasized brisk walking, but also other activities with equivalent intensity (aerobic dance, bicycle riding, skating, and swimming) were recommended. The participants were advised to distribute the physical activity throughout the week, with at least 10 minutes per session. Voluntary, supervised physical activity sessions were offered at least twice per week throughout the study, including group walks, aerobic classes, and one-to-one personal training. After an average follow-up of 2.8 years, the incidence of diabetes was 11.0, 7.8 and 4.8 cases per 100 person-years in the placebo, metformin and lifestyle groups, respectively. The lifestyle intervention reduced the incidence by 58% and metformin by 31%, as compared with placebo.
Furthermore, the Indian Diabetes Prevention Program and the Japanese Prevention trial also reported a risk reduction of people with impaired glucose tolerance that underwent a lifestyle intervention program. However, they did not report separately the results of the effect of the increase in physical activity levels.
Finally, until very recent, it was unclear whether weight training, either alone or combined with aerobic exercise, is effective for the prevention of type 2 diabetes. However, a recent prospective cohort study that included 32,002 men from the Health Professionals Follow-up Study showed now that weight training or aerobic exercise for at least 150 minutes per week are both independently associated with a lower risk of type 2 diabetes and that combining both forms of exercise is associated with the greatest reduction in risk of type 2 diabetes.
A community event realzied two years ago (Walking for Diabetes) during the World Diabetes DayAs it is very important to implement scientific research findings into clinical practice, future research should be focused on how to increase the motivation of physicians in prescribing physical activity. In addition, studies are needed to evaluate activity-prescription schemes that are sustainable in everyday use for the people at risk of type 2 diabetes. Epidemiological evidence has shown that physical activity is of medical benefit, not just for preventing diabetes, but also for cardiovascular health and quality of life. Thus, public health messages, health care professionals, and health care system should promote physical activity.
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