Background: Persons with impaired glucose tolerance have a high risk of developing type 2 diabetes. Many lifestyle, herbal, and pharmacologic interventions have been studied to prevent or significantly delay this progression; however, the relative effectiveness of these interventions is unclear. The rapidly increasing incidence of diabetes makes gaining information about the most effective preventive strategies of critical importance. Gillies and colleagues conducted a meta-analysis to compare the effectiveness of pharmacologic and lifestyle interventions in preventing or delaying the development of type 2 diabetes.

The Study: To identify relevant studies, the authors used electronic databases, references of published studies and reviews, and expert recommendations. Inclusion was limited to good-quality randomized controlled trials that clearly defined patients with impaired glucose tolerance and included the development of diabetes as the primary outcome measure. Three reviewers had to approve each study for inclusion in the meta-analysis.

From more than 11,000 identified articles, 17 trials with 8,084 total participants were included in the meta-analysis. Pharmacologic interventions were orlistat (Xenical), oral diabetes medication, and the jiangtang bushen herbal regimen. Lifestyle interventions comprised diet and/or exercise.

Results: All interventions were effective in preventing or delaying diabetes. When considered separately, diet, exercise, and a combination each had a relative risk reduction of 49 percent. The pooled effect for all lifestyle interventions had a hazard ratio of 0.51; this was equivalent to a number needed to treat (NNT) of 6.4. Lifestyle interventions were more effective in participants with initially higher body mass indices. Oral diabetes medication and orlistat also were highly beneficial with pooled hazard ratios of 0.70 and 0.44, respectively. The herbal regimen had a hazard ratio of 0.32. The NNTs for diabetes medication, orlistat, and the herbal regimen were 10.8, 5.4, and 4.0, respectively. Adverse events were mainly gastrointestinal upsets related to medications; the reported incidence of adverse events varied widely among trials.

Conclusion: The authors conclude that lifestyle and pharmacologic interventions equally reduce progression to type 2 diabetes in persons with impaired glucose tolerance. These interventions can halve the risk of diabetes in these patient. A clear understanding of potential adverse effects of long-term pharmacologic therapy is needed for an accurate risk-benefit assessment.