This speculation gained further support following the report of Heiss et al. that consumption of a single flavanol-rich cocoa beverage could transiently improve forearm brachial artery flow-mediated vasodilation. Importantly, this observation correlated with increased levels of bioavailable NO measured in the blood. Neither an increase in flow-mediated vasodilation nor an increase in bioavailable NO was observed when subjects consumed a low-flavanol cocoa beverage.The increase in bioavailable NO observed in vivo is consistent with the hypothesis raised by Karim et al., that the vascular action of cocoa flavanols is, in part, due to their ability to influence NO status.
This hypothesis was confirmed by Fisher et al. in the human study that demonstrated an activation of the NO system following the consumption of a flavanol-rich cocoa beverage.
Most recently, a study in smokers - a group known to have poor vascular reactivity - demonstrated that the consumption of a cocoa drink rich in flavanols led to significant increases in circulating NO and flow-mediated dilation. These changes were correlated with increases in flavanol metabolites in plasma. Taken together, these human in vivo studies provide support for the concept that cocoa flavanols may help to support cardiovascular health.
Cocoa Flavanols in the Diet
Flavanols are a specific class of compounds within the much larger family of polyphenolic compounds known as flavonoids. They occur naturally in a variety of plant-based foods and beverages, including cocoas, chocolates, teas, red wines, fruits, cereals, beans, spices, and nuts. The US Department of Agriculture (USDA) is developing a database that contains information on the flavanol content in many foods and this can be accessed via their website (see Figure 1). The monomeric flavanols (epicatechin and catechin) and the oligomeric flavanols (procyanidins) are present in cocoas and chocolates to a varying extent, depending on the type of cocoa and food processing techniques used to make the finished product.