In a head-to-head comparison over 15 years, diet and exercise outperformed the drug metformin in preventing people at high risk for diabetes from developing the disease.
Metformin, which helps control blood sugar and can be used alone or in combination with insulin to treat type 2 diabetes, also lowered the risk of developing the disorder in the study group, but not as much as making healthy lifestyle changes did.
The study revealed that in some people, lifestyle intervention had an even more powerful effect – in particular, those older than age 60. Metformin was relatively more effective in people younger and in those who were more obese.
Participants were enrolled in the Diabetes Prevention Program, a randomized trial that originally lasted three years and compared people assigned to either an intensive lifestyle intervention or 850 milligrams of metformin twice daily and a group taking a placebo.
The participants were all overweight or obese and had elevated blood sugar levels, both factors that put them at very high risk for developing Type 2 diabetes.
At the end of that three-year study, the people following the lifestyle intervention, which included a low-fat, low-calorie diet and 15 minutes of moderate-intensity exercise daily, had a 58 percent lower risk of having developed Type 2 diabetes compared to the placebo group. Those taking metformin were 31 percent less likely to have progressed to diabetes than those on placebo.
Since the lifestyle intervention had worked so well, all participants were offered a version of it for one year after the study concluded.
As of 2014, almost 90 percent of the original study group, or 2,776 people, had been followed since the end of the first three-year study, and based on their original group assignments, they were offered lifestyle reinforcement seminars twice yearly or continued to receive metformin.
After an average of 15 years, diabetes incidence was lower by 27 percent in the lifestyle intervention group and 18 percent in the metformin group compared to the placebo group.
In 2014, 55 percent of the lifestyle group, 56 percent of the metformin group and 62 percent of the placebo group had been diagnosed with diabetes.
The researchers also tested for changes in the tiny blood vessels of the kidney and retina and for nerve damage over time, all of which are associated with diabetes. The presence of these complications did not differ between groups overall. But among women in particular, the lifestyle group was less likely to show this kind of damage.
People who did not develop diabetes were almost 30 percent less likely to have kidney, retina or nerve damage than those who did.
It was surprising that although lifestyle changes did reduce the risk of diabetes, they did not always reduce the risk of microvascular complications. The researchers stated “Metformin could be especially useful in people who are unable to follow diet and exercise strictly, who are obese, have polycystic ovarian disease, or cannot walk or exercise due to physical infirmity”.
However, lifestyle interventions should be the first choice for diabetes prevention, with metformin recommended for younger and more obese people.
Source: The Lancet Diabetes and Endocrinology, online September 13, 2015.
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