No cream cakes and lots of exercise may have been joined by a much more palatable way of helping keep your heart healthy - eating chocolate.

Although the trial that showed the beneficial effects had only involved a total 40 people, Professor Carl Keen, who led the research, said the results were "remarkably robust".

Another reason for scepticism could be that the research was sponsored by chocolate makers Mars, but Professor Keen, from the University of California, Davis (UCD), said: "I think that responsible food companies should sponsor research into their products.

"And of course people should always be sceptical until results are repeated and published in peer-reviewed journals." The work is currently under review in two international journals.

The research team, from UCD and Mars, gave the subjects a tablespoonful of cocoa in water to drink - control subjects received plain water. After two hours, they saw that in the test group the time that blood took to clot was reduced.

High concentration

This is beneficial, explained Professor Keen, because "blood platelets can become hyperactive and clot, which can lead to heart attacks and strokes".

Historical uses for chocolate

Weight gain for undernourished Treating tuberculosis Calming agitated people Soothing stomachs and aiding digestion Masking bitter tastes

The effect had almost gone after six hours.

The component of chocolate most likely to be responsible for the effect are molecules called flavinoids. These have been credited with similar beneficial effects in tea and wine, but cocoa has a particularly high concentration.

The fat and sugar in chocolate could have detrimental effects on the body but Professor Keen said: "One should view chocolate as being part of a healthy diet - I don't have any guilt when I eat it."

The professor reported his findings at the American Association of the Advancement of Science's (AAAS) annual expo in Washington DC.