Researchers compared the effects of dark (74% cocoa solids) and white chocolate on the smoothness of arterial blood flow in 20 male smokers.
In smokers the activity of both endothelial cells, which line the artery walls, and platelets, which are involved in the formation of blood clots, are continuously disrupted, making the arteries susceptible to the narrowing and hardening characteristic of coronary artery disease.
Before eating 40 g of chocolate (about 2 oz), smokers were first asked to abstain from other foods rich in antioxidants, such as onions, apples, cabbage, and cocoa products for 24 hours.
After two hours, ultrasound scans revealed that dark chocolate significantly improved the smoothness of arterial flow, an effect which lasted for eight hours. Blood sample analysis also showed that dark chocolate almost halved platelet activity. Antioxidant levels rose sharply after two hours.
White chocolate had no effect on endothelial cells, platelets, or antioxidant levels.
Dark chocolate has more antioxidants per gram than other foods laden with the substances, such as red wine, green tea, and berry fruits, say the authors, who suggest that the beneficial effects of dark chocolate lie in its antioxidant content.
"Only a small daily treat of dark chocolate may substantially increase the amount of antioxidant intake and beneficially affect vascular health," conclude the authors.