Zurich, Switzerland - Another study—this time randomized and double-blind—has found that flavonoid-rich dark chocolate might be good for the heart [1]. Writing in the November 20, 2007 issue of Circulation, Dr Andreas J Flammer (Cardiovascular Center, Zurich, Switzerland) and colleagues report that compared with "cocoa-free" chocolate, a dark chocolate rich in flavonoids induced coronary vasodilation and reduced platelet adhesion in heart-transplant recipients, even on top of standard secondary-prevention CVD drugs.

The authors say the findings suggest a role for this type of chocolate in preventing graft atherosclerosis in transplant recipients and possibly in reducing the risk of atherosclerosis in a wider population.

"This beneficial potential provides a strong rationale to further investigate the clinical effects of cocoa in cardiovascular disease," the authors write.

Commenting on the study for heartwire, Dr Franz H Messerli (Columbia University, New York) said the results were an important part of an ongoing story.

"I don't think we can conclude that dark chocolate is going to be the next nitroglycerin, but still. . . . This is the first study that shows that, indeed, chocolate improves coronary blood flow, and significantly so, in patients who already were on vasodilators—ACE inhibitors and beta blockers," he said. "So over and above conventional therapy, when you give dark chocolate at the dose it was given in this study, you get improved coronary blood flow."

Flammer and colleagues assessed coronary vasomotion using quantitative coronary angiography and cold-pressor testing before and two hours after giving 22 heart transplant recipients 40 g of dark chocolate (70% cocoa) or cocoa-free chocolate. On the second measurement, coronary artery diameter increased significantly from baseline, endothelium-dependent coronary vasomotion improved, and platelet adhesion decreased in the flavonoid-rich group. No significant changes were seen in the group eating the control chocolate.

To assess whether these improvements paralleled changes in serum antioxidants, Flammer et al also measured concentrations of flavanols (a flavonoid subclass) in the serum and found that epicatechin concentrations correlated with coronary vasomotion, but catechin concentrations did not. This last observation adds weight to hypothesis that epicatechin is a "possible mediator" of improved coronary vasomotion with chocolate consumption, the authors note.

"Our results suggest a short-term effect of flavonoid-rich dark chocolate in terms of inducing coronary vasodilation and improving coronary vasomotion and shear-stress-dependent platelet adhesion, which results in the potential to beneficially affect atherothrombosis," they conclude.

In an accompanying editorial [2], Drs Norman Hollenberg and Naomi DL Fisher (Brigham and Women's Hospital, Boston, MA) note that despite the evidence amassing in support of chocolate's cardioprotective properties, physicians, the public, and the mainstream media must be wary of interpreting the results. For one, they write, the term "dark" is misleading, since color can have nothing to do with flavanol content, and many manufacturers actually use processing techniques that destroy flavanols, even when the product tastes (and is labeled) "dark."

"If the industry wants us to use chocolate as a health food, then they will have to change their behavior," the editorialists write. "Specifically, what the world needs is a label on each package that describes the flavanol content of the chocolate. It should be obvious that the percentage of cocoa, like the color of chocolate, does not represent a measure of flavanols at all. . . . Probably the most effective mechanism is for the lay press to stop talking about dark chocolate or percent cocoa and start discussing flavanol content."

But an even bigger hurdle will be determining the true "health benefits" of chocolate in a large, well-designed, appropriately controlled trial—an expensive prospect in the nutrition industry, they note, where a positive study "does not create intellectual property," making it difficult for a company to justify the expense of the trial as an investment.

"This is a problem we have to overcome if we are to obtain the evidence that we need to make appropriate recommendations to the community," Hollenberg and Fisher write. To heartwire, Messerli mentioned that he knows of at least one company attempting to study chocolate's antihypertensive effects in a large, well-designed trial.

Messerli, as well as the editorialists, points out that any evidence of cocoa's antioxidant health benefits do not outweigh some of the hazards of overindulging in what is for many a favorite treat.

"We still have to consider the caloric load: there's absolutely no question that chocolate is very high in calories and fairly high in fat," Messerli said. "But it's no longer an absolute no-no, as it used to be."