The molecule, called resveratrol, is found in red grapes or wine.

Previous research has revealed the substance has anti-ageing effects in some organisms, extending the lifespan of yeast by 60%, worms and flies by 30%, and fish by about 60%.

It has also been suggested the reported health benefit of red wine may also be down to the resveratrol.

Healthier mice

To investigate the effects of the molecule on mammals, the researchers looked at middle-aged mice fed on a high-calorie diet, with 60% of the calories coming from fat.

These mice shared many of the problems of humans on an equivalent diet, including obesity, insulin resistance and heart disease.

They discovered the mice given resveratrol alongside their food did not lose weight but they showed decreased glucose levels, healthier hearts and liver tissue, and better motor function compared with the mice on the same diet but without the supplement.

The mice's health was almost in line with that of mice fed on a standard diet, the researchers found.

They also discovered the chemical was improving the mice's life-span. The scientists estimated resveratrol reduced the risk of death in the mice by about 31%, a point similar to the lifespan for the standard diet mice.

The exact mechanism of the chemical is not yet known, but the researchers believe it may be activating a gene called SIRT1, which is linked to a family of proteins thought to be involved with longevity.

Researcher on the study, Dr Rafael de Cabo, from the National Institute on Aging at Harvard Medical School, said: "After six months, resveratrol essentially prevented most of the negative effects of the high calorie diet in mice."

His colleague David Sinclair, associate professor of pathology at Harvard Medical School, said: "The 'healthspan' benefits we saw in the obese mice treated with resveratrol are positive clinical indicators and may mean we can stave of in humans age-related diseases such as type 2 diabetes, heart disease and cancer, but only time and more research will tell."

'Sit back and relax'

In an accompanying article in the journal, Professor Peter Rabinovitch, from the University of Washington, said the findings were potentially good news for humans, but added a note of caution.

"The safety of resveratrol at the high doses in humans comparable to those used by [the researchers] is unknown, especially over the course of years or even decades, when relatively modest side-effects could have dramatic consequences."

He said the next step for the researchers should be to investigate the effects of the chemical in humans.

"For now, we counsel patience. Just sit back and relax with a glass of red wine - which alas, has only 0.3% of the relative resveratrol dose given to the gluttonous mice."

Professor Steve Bloom, head of an obesity research group at Imperial College, London, said: "If we start with the idea that there is an evolutionary advantage for the life expectation of each species, and this is tied into scarcity or abundance of food.

"If there is plenty of food, you'll live a very active life for a while, and then drop dead.

"If there isn't much food, because reproduction takes more energy, it is better to keep a small number of animals going for longer.

"There is a system to regulate it, and it looks like resveratrol bypasses this system or may be an endogenous part of that system.

"This paper is extremely interesting - it could be the breakthrough of the year, with massive possibilities for treating human beings."