Researchers at the Universite Louis Pasteur de Strasbourg were examining the effect on the heart of Concord grape juice.

"Grape juice can have a similar effect (against heart disease) as red wine but without the alcohol. That is a very important message," said Dr Valerie Schini-Kerth, lead author of the study published in the journal Cardiovascular Research.

Red wine and certain types of grape juice have high levels of polyphenols, which block the production of a protein linked to cardiovascular disease -- the number one killer in many Western countries.

Heart and vascular problems develop when endothelial cells that make up blood vessels do not work properly.

Schini-Kerth and her team found that polyphenols in Concord grape juice activate endothelial cells to produce nitric oxide which helps to protect against cardiovascular disease and to maintain healthy blood vessels and blood pressure.

Polyphenols work the same way in red wine and in grape juice.

"But not every grape juice has the beneficial effect. It has to have a high level of polyphenols," Schini-Kerth said.

The amount of polyphenols in grape juice, as in red wine, depends on the type of grape used and how it is processed.

"We have information on more than 100 different kinds of wine and the amount of polyphenols. What we know is that the most protective ones have the highest levels of polyphenols. That is established," she said.

But Schini-Kerth, whose research was partly funded by Welch Foods Inc which is a leading producer of grape juice, said little information is available on the levels of polyphenols in grape juice.

The scientists were studying cells from pigs, which provide a good model for studying human cells.

They were looking at healthy blood vessels and are planning a further study to see whether grape juice has a similar impact on blood vessels that show signs of cardiovascular disease.