Scientists may have discovered the reason why red wine appears to protect the heart.

Numerous studies have suggested that moderate alcohol drinking helps to reduce the likelihood of heart disease.

The so-called "Mediterranean diet", which includes a larger intake of wine, has been credited with lower rates of heart disease in those countries, despite a higher intake of saturated fats.

However, there is no clear evidence that red wine is any better than any other alcoholic drink.

But a team of scientists from Barts and the London School of Medicine, and the Queen Mary University in London, may have found a mechanism which points to the benefits of red wine.

They say it appears to interfere with the production of a body chemical which is vital to the process which clogs up arteries and increases the risk of a heart attack.

Wines tested

That chemical, a protein called endothelin-1 (ET-1), has already been shown to be involved in the formation of early signs of artery disease, such as the formation of fatty streaks on the walls of arteries.

Chemicals which work against it have been shown to reduce the rate of heart attacks in people who have heart disease.

The London team tested extracts from 23 red wines, four white wines, a rosé wine and one red non-alcoholic grape juice sample, after finding that certain chemicals - called polyphenols - from Cabernet Sauvignon grapes decreased the manufacture of ET-1 in bovine artery wall cells.

They found that, in the red wines, the amount they inhibited ET-1 ran parallel with the amount of these polyphenols they contained.

The white and rosé wines had no similar effect.

Cabernet the best

Dr Roger Corder, from the William Harvey Research Institute at St Barts, said: "What we are proposing is the mechanism that could explain why red wine is a better alcoholic beverage to consume than others.

"If you consume one glass of red wine and you have a good absorption of the active principle, that would be more than adequate."

He said that Cabernet Sauvignon-derived wines seemed to have the most impact.

The study is published in the journal Nature.