Diabetes Drug and Exercise Don't Mix

Prediabetic patients benefit less from exercise when metformin is added

(RxWiki News) Exercise and metformin - a commonly prescribed diabetes drug - are both valuable treatments for preventing diabetes. Used separately, the treatments work well. In combination, however, they may be less effective.

For people with type 2 diabetes, exercise and metformin each improve resistance to insulin, a hormone that manages blood sugar. However, when the treatments were used together, metformin reduced the positive effects of a 12-week exercise program for people with pre-diabetes.

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Barry Braun, Ph.D., of the University of Massachusetts Amherst, and colleagues set out to test the effectiveness of certain methods for preventing type 2 diabetes. They expected to find that combining drug treatment with an exercise program would improve blood sugar levels more than either treatment on its own. However, their findings were surprising.

According to Dr. Braun, "Exercise combined with metformin was not better than exercise alone and it might even be worse."

From their study of 32 pre-diabetic men and women, the researchers found that adding metformin to an exercise program lessened the beneficial effects of exercise by 25 to 30 percent.

"We're now trying to understand the mechanisms to explain this," says Dr. Braun.

For their study, the researchers separated participants into one of four treatment groups: a 12-week exercise program, exercise plus metformin, metformin only, or no treatment. The exercise program involved 60 to 75 minutes of aerobic exercise (swimming, biking, walking, etc.) and resistance training three times per week.

The researchers also measured participants' insulin sensitivity at the beginning and end of the 12-week treatment period.

All of the treatment groups showed better insulin sensitivity, which means that the hormone insulin became a more effective regulator of their blood sugar levels. Only those who took metformin lost weight. However, adding metformin to the exercise program did not improve the effects of exercise.

While more research is needed to understand why metformin blunts the beneficial effects of exercise, Dr. Braun and colleagues believe it may be related to the way that metformin affects the muscles, liver, and insulin-producing cells of the pancreas.

They suspect that these parts of the body may react differently to exercise when metformin is present.

This research - which was funded by the American Diabetes Association and the National Institutes of Health - is published in the journal Diabetes Care.

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Review Date: 
December 7, 2011