Can Meformin Prevent or Delay Type 2 Diabetes?

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Meta-analysis: metformin treatment in persons at risk for diabetes mellitus, by Shelley R. Salpeter and colleagues. American Journal of Medicine 121:149-157, 2008

What is the problem and what is known about it so far?

Diabetes is a worldwide epidemic. The disease reduces quality of life, is associated with life-threatening complications, and presents a huge cost burden to society. Diet and exercise can help people avoid diabetes, but finding other effective ways to prevent diabetes, including medicines, is also important. Metformin, a drug that reduces weight and insulin resistance in people with diabetes, also reduces new cases of diabetes among people at risk.

Why did researchers do this particular study?

The researchers wanted to learn more about how metformin can help people avoid diabetes and how much it may be able to reduce the rate of new-onset diabetes among people at risk.

Who was studied?

Data was analyzed for a total of 4,570 nondiabetic subjects from 31 previous studies of metformin therapy.

How was the study done?

Researchers performed a meta-analysis (a study that combines and analyzes data from other previous studies) of 31 studies comparing metformin with "dummy" pills or no treatment in people without diabetes. They examined data about body mass index (a measure of overweight), fasting glucose and insulin levels, insulin resistance, cholesterol levels, and the number of cases of new-onset diabetes in these studies.

What did the researchers find?

Metformin reduced the number of new cases of diabetes by 40%. It reduced body mass index, fasting glucose and insulin levels, insulin resistance, LDL ("bad") cholesterol, and blood fats known as triglycerides and increased HDL ("good') cholesterol compared to either dummy pills or no treatment.

What were the limitations of the study?

This study looked at diabetes risk factors—not outcomes, such as heart disease. Some of the studies were short and might not have lasted long enough to show a decrease in new cases of diabetes. This may have resulted in underestimation of metformin’s ability to prevent new cases of diabetes. Insulin resistance was calculated instead of directly measured; however, such calculations are generally accurate. The 31 studies had all been published, so there may have been bias toward studies showing greater effects, which are more likely to be accepted for publication. Because diabetes is often diagnosed through fasting glucose or glucose tolerance tests, metformin could have masked some new cases. However, one study that postponed diabetes testing until 2 weeks after metformin was stopped still found significant reductions in new diagnoses. Finally, because most of the trials also included diet and exercise recommendations, it is unclear how much of the reduction in new diabetes came from lifestyle and how much came from metformin. Intensive lifestyle therapy prevents diabetes better than metformin, and combining lifestyle change and metformin prevents diabetes better than either therapy does separately.

What are the implications of the study?

Metformin therapy in people who are at risk for diabetes improves weight, blood fats, and insulin resistance and reduces new-onset diabetes by 40%. Intensive lifestyle change is the best approach for those at risk for diabetes. However metformin should be added when diet and exercise alone are not enough. Future studies are needed to determine whether preventive metformin treatment results in reductions in outcomes such as heart disease and death.

FOR MORE INFORMATION

Diabetes risk test

Preventing or delaying diabetes

Obesity and Diabetes Epidemic