Researchers say they have discovered the key component in red wine that explains the so-called French Paradox, or the way the French can eat lots of cheese, buttery sauces and other rich foods and still suffer less heart disease than Americans.
The explanation is pigments known as polyphenols.
The pigments are not present in white wine or rose, and they seem to be less potent when they are present in grape juice.
Polyphenols inhibit the production of a peptide that contributes to hardening of the arteries, researchers report in Thursday's issue of the journal Nature.
In laboratory dish experiments, polyphenols in red wine decreased the amount of the peptide endothelin-1 produced by cells taken from the blood vessels of cows.
Endothelin-1 is a potent blood vessel constrictor, and overproduction of the compound is thought to be a key factor in why arteries clog with fatty deposits, said the researchers from the William Harvey Research Institute at the London School of Medicine & Dentistry.
In the study, the cow cells were exposed to extracts from 23 red wines, four white wines, one rose and one type of red grape juice.
Researchers found the decrease in endothelin-1 levels was related to the amount of polyphenols in the wines.
The white and rose wines _ which contain little or none of the pigment _ had no effect on endothelin-1 levels.
Red grape juice, which has plenty of the pigment, was markedly less potent in reducing endothelin-1 than red wine. The researchers said that suggests that something in the winemaking process changes the pigment's properties.
Researchers believe the pigment comes from red wine skins. In white wine and rose, the grape skins are taken out before fermentation.
The type of grape also appeared to matter. Four of the six most effective red wines used in the study were made entirely or partially from cabernet sauvignon grapes.
``The key message is moderate consumption of red wine is likely to prevent heart disease, but we have no evidence that white wine or rose would have a similar benefit,'' said Roger Corder, who led the study.
The lower incidence of heart disease in France, despite a diet rich in butter and other fats, has led researchers to look to the consumption of red wine, another staple of the French diet.
Other studies have shown red wine helps fight heart disease, and scientists have theorized that the benefits are caused by antioxidant compounds that prevent or slow the damaging effects of oxygen on the body.
Corder's research shows a different mechanism altogether. He said it is a more plausible explanation for the French Paradox.
David Klurfeld, a researcher at Wayne State University who linked red wine and a reduction in heart disease in 1981, noted that the cells were tested in a dish and said it is unclear how polyphenols work in the body. However, he said, the research opens another pathway that should be pursued.
``Is this the only mechanism, or is it a combination? There's not enough evidence that points us in any direction,'' Klurfeld said. ``We're basically playing spin the wine bottle here.''