Image caption Mouse studies gave "promising" results

A diabetes pill has anti-ageing effects and extends the life of male mice, research suggests.

Scientists believe the drug, metformin, may mimic the effects of extreme calorie restriction.

This regime, which is based on eating a very low calorie diet, is thought to promote healthy ageing.

The human implications of the study are unclear, the researchers report in the journal, Nature Communications.

Rafael de Cabo, of the National Institute on Ageing in Baltimore, Maryland, US, said calorie restriction in laboratory animals had been shown to increase their lifespan.

His team is searching for interventions - such as a drug - that can mimic these effects.

Right now the best that we can say is probably what your grandmother told you... eat a good diet and exercise Dr Rafael de Cabo, National Institute on Ageing

Metformin is one of the most widely prescribed treatments for type-2 diabetes, which occurs mainly in people above the age of 40. It is also used to treat metabolic syndrome, a combination of diabetes, high blood pressure and obesity.

Previous work has shown that metformin can extend the lifespan of simple organisms such as worms, but studies in flies and mammals have given conflicting evidence.

The scientists gave one of two different doses of metformin to middle-aged male mice and found that lower doses increased lifespan by about 5%, and also delayed the onset of age-associated diseases. But they said the higher dose of metformin was toxic and reduced the lifespan of mice.

Further studies were needed to determine if metformin has any effect on human health and lifespan, said Dr de Cabo.

"These are very promising results that need to be translated to humans via clinical studies," he said.

He said the best current advice was to eat a good diet and exercise.

"Right now the best that we can say is probably what your grandmother told you," he told BBC News.

"Eat a good diet and exercise are the only two things that we know for sure that they work very well in humans."

'Note of caution'

Prof Tom Kirkwood, associate dean for ageing at Newcastle University, said it is unclear what the study might mean for human health.

"Metformin is a well-established drug that acts on metabolism and has long been used against type-2 diabetes," he said.

"We've known for a long time that modulating metabolism in mice can extend survival and postpone age-related conditions, and there are sound reasons why this should be the case is a small, short-lived animal.

"What we don't know however is whether similar effects on lifespan might be produced in humans.

"This is something that we cannot simply take for granted and the study's authors do well to sound a note of caution."