A diabetes drug given in low doses may have anti-ageing effects, US scientists have said following an experiment with mice.

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

Eating a very low calorie diet is thought to promote healthy ageing, BBC reported.

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

However, the human implications of the study were unclear, the researchers said in the journal Nature Communications.

Metformin is a widely prescribed treatment 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.

Earlier work has shown that metformin can extend the lifespan of simple organisms like 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 five percent, 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, BBC reported.

De Cabo said further studies were needed to determine if metformin has any effect on human health and lifespan.