Previous studies in humans have credited a diabetes drug called metformin with reducing the risks of developing pancreatic cancer and breast cancer. Another study found that ovarian cancer patients taking metformin for their diabetes lived longer than those who did not take the drug. Given these findings, Rafael de Cabo of the National Institute on Aging (Baltimore, MD) thought that metformin might be a good candidate for studying ways to improve aging and lengthen lifespan.

When de Cabo and his team gave a small dose of metformin to middle-aged mice, the drug boosted their health and extended their lives (Nat. Commun. published online 30 July 2013; doi:10.1038/ncomms3192 ). The scientists tested two doses of the drug. Mice that were given 0.1% metformin mixed into their diets lived almost 6% longer than untreated mice: the treated mice lived 160 weeks, while those not given the drug lived about 150 weeks. But when mice were given 1% metformin in their diets, their lifespans were shortened by about 14% compared to untreated mice. The latter result was likely due to the toxicity of the high dose, which induced kidney failure in the mice.

Aging is a driving force behind metabolic syndrome, which is a predisposing condition for type 2 diabetes and heart disease. Metformin is clinically proven to alleviate symptoms of diabetes, improving insulin sensitivity, spurring the conversion of sugar to energy and preventing the buildup of sugar in the liver. In the treated mice, 0.1% metformin appeared to burn more fat for energy, keep the mice's body weight low, increase the animals' antioxidant responses to cell stress, reduce inflammation and prevent the onset of metabolic syndrome.

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The study's findings suggest that metformin may mimic some of the previously reported health benefits of calorie restriction, or limiting the amount of calories taken in each day from food. In this study, the diets of the mice were not calorie-restricted. In fact, treated mice ate more calories than the untreated mice. This suggests that the drug may provide the benefits of calorie restriction without requiring food deprivation.

Studies in humans will have to confirm the results seen in these mice. The researchers point out that the lower dose of metformin used in the study led to blood levels in the mice that were 10 times higher than those in human patients treated with the drug for diabetes.