A study out of  the Yale Prevention Research Center in Connecticut has found that the cocoa in dark chocolate may be able to boost the function of endothelial cells that line the inside of blood vessels. Cocoa contains a group of antioxidant compounds called flavonoids which are also found in fruits and vegetables, wine and green tea. The action of the flavonoids on the endothelial cells is what may help decrease the risk of cardiovascular disease.

The study included 45 healthy people which were divided into three groups that ate either eight ounces of cocoa without sugar; cocoa with sugar; or a placebo. They also underwent endothelial function testing using a high frequency ultrasound to measure flow mediated dilation (FMD). They found that the FMD improved significantly in 2.4% of the group who consumed cocoa with no sugar, and 1.5% percent of those who ate cocoa with sugar.  There was a 0.8% percent decrease in FMD in the group that ate the placebo.

Researchers believe that the significant improvement in endothelial function seen in this study could be further investigated in a long-term, randomized clinical trial.  They state that at this time they do not suggest making dark chocolate a  part of someone's daily routine, but only that we start to explore what cardiovascular benefits flavonoid-rich foods might offer.