"Only a small daily treat of dark chocolate may substantially increase the amount of antioxidant intake and beneficially effect vascular health," said Dr F. Hermann and colleagues from University Hospital, Zurich.
Dark chocolate is a rich source of antioxidants, and contains more polyphenols per gram than green tea or red wine.
The research, published in the journal Heart (vol 92, pp 119-120), compared the effects of dark or white chocolate on blood flow and the platelet activity of 20 healthy male smokers.
Smokers were chosen as the study group because smoking is a major risk factor in cardiovascular health. Endothelial cells, which line the walls of the arteries, are affected by cigarette smoke, both passive and active. Platelets contribute to blood clotting and then to thrombosis.
The volunteers were randomly divided into two groups and, after a 24-hour period of abstinence from polyphenol rich foods, were given 40g of dark or white chocolate.
"Dark but not white chocolate induced a rapid and significant improvement of endothelial and platelet function in healthy smokers two to eight hours after ingestion," said the researchers.
"The high flavonoid content of dark chocolate may potentially explain the mechanisms for the reduced platelet activation," explained Hermann.
Endothelium dysfuntion is caused by reactive oxygen species, but the high antioxidant content of the dark chocolate slows or blocks these destructive species.
The new study adds to a growing body of research about the beneficial effects of chocolate on heart health. Previous studies published in the American Journal of Hypertension (Vol. 18, Issue 6, pp. 785-791) and the Journal of the American College of Cardiology (Vol. 46, pp.1276-1283), also reported positive effects of dark chocolate on the health of smokers' blood vessels.
Other studies have claimed promising results against a wide range of conditions including blood pressure, diarrhoea, breast cancer prevention and decreasing the effects of aging on the brain.
The Zurich researchers were careful to stress that further research is required to study the long-term effects of polyphenols on health. Moderation with chocolate consumption was also stressed particularly since it may adversely affect heart health because of sugar and fat content.
The chocolate industry has however already profited from the wave of positive health effect of cocoa, with producers increasingly highlighting polyphenol content on their labels.
CocoaVia, from Mars, and Acticoa, by Barry Callebaut, both boast high polyphenol content and are marketed as healthy options. The Mars Nutrition for Health & Well-Being is a new range from the confectionary giant aimed at consumers who want to be healthy but are reluctant to give up chocolate completely.