Several large studies were published on prevention of diabetes type 2 by exercise combined with other interventions such as weight loss and intensified medical treatment.  In one study 3234 nondiabetic patients with impaired glucose tolerance were randomly assigned to either placebo, metformin (850 mg twice daily), and lifestyle-modification program with the goals of a minimum of 7% weight loss and 150 min physical activity per week (52).

Physical activity was only recommended, not supervised; adherence to the intervention was assessed by a log book kept by the patient. The mean age of the participants was 51 years and average follow-up was 2.8 years.

By the end of the curriculum (24 weeks) 50% of the participants in the lifestyle-intervention group had reached the goal of 7% weight loss,  which decreased to 38%  at the most recent visit,  however.  The proportion of participants who met the goal of 150 min physical activity per week was 74% at 24 weeks, and 58% at the most recent visit.

Patients assigned to the lifestyle intervention had a much greater weight loss and greater increase in leisure time physical activity than did participants assigned to placebo or metformin. The average weight loss was 0.1, 2.1, and 5.6 kg in the placebo, metformin, and lifestyle-intervention groups, respectively (p

< .001).

The incidence of diabetes was reduced by 58% in the lifestyle-intervention group, and by 31% in the metformin group, as compared to placebo. Rates of adverse events, hospitalizations, and mortality were similar in both groups. The number needed-to-treat was 6.9 for the lifestyle-intervention, and 13.9 for the metformin group.

Combined effects of lifestyle factors were examined in a large study for which 84,941 nurses were recruited between 1980 and 1996

(53). During 16 years of follow-up 3300 new cases of diabetes type 2 were documented.

Overweight or obesity were the single most important predictor of diabetes, but lack of exercise, poor diet, and current smoking were also associated significantly with an increased risk of diabetes.

The risk of developing diabetes type 2 could be lowered by 90%  by adhering consistently to lifestyle characteristics such as maintaining a body mass index below 25,  exercising regularly,  eating a prudent diet, abstaining from smoking, and consuming alcohol moderately.

In a large study from China 577 individuals with impaired glucose tolerance were randomized to four different groups: diet only, exercise only, diet plus exercise, and control (54).  At 6 years the cumulative incidence of diabetes was 67.7%  in the control group as compared to 43.8% in the diet group, 41.1% in the exercise group, and 46.0% in the diet plus exercise group (p

< .05).

CONCLUSIONS
Physical inactivity has been identified as one of the most important risk factors for developing diabetes type 2. Ninety percent of type 2 cases can be accounted for by a combination of physical inactivity, overweight, and dietary problems.

A number of mechanisms have been clarified by which regular exercise is capable of repairing or at least ameliorating the effects of the western lifestyle:  expression of eNOS in endothelial cells,  mobilization of endothelial precursor cells from the bone marrow, increasing insulin sensitivity in skeletal muscles, and normalizing and maintaining body weight. 

However,  the therapeutic value of physical exercise, although proven beyond any doubt, is severely limited by the inability of the vast majority of patients to implement and maintain lifestyle changes without constant supervision. Adherence to any interventional program advocating regular physical exercise and weight reduction is short-lived and haphazard.  Moreover,  it can be safely assumed that patients recruited for such a trial represent a positive selection from the large pool of patients not even considering to participate.

In the face of a relentless and accelerating increase of the incidence of type 2 diabetes new strategies are urgently needed to deal with this problem.  We have to face the fact that the majority of trials conducted in adults have yielded disappointing long-term results, demonstrating that patient motivation is the limiting factor in these interventions.

Impressive results are usually limited to a brief period of close supervision only to be eroded slowly as soon as the patient returns to normal life.  Now it is time to shift the focus of attention to the young generation.  The epidemic of overweight and physical inactivity has already arrived in this age bracket,  but there is still hope that changes in lifestyle achieved in school children or even in kindergarten may be longer lasting and perhaps permanent.

Gerhard Schuler and Axel Linke
Department of Internal Medicine/Cardiology, University of Leipzig, Leipzig, Germany

REFERENCES