Previous research has already shown that flavonols protect blood vessel health and it is therefore thought that they should benefit the heart. But the new study, reported in the 4 October issue of the Journal of the American College of Cardiology (vol 46, pp1276-1283), is important because it demonstrates these benefits in smokers, people that have raised risk of heart disease.
Smokers' blood vessels tend to respond poorly to changes in blood flow, possibly related to impairments in how nitric oxide sends signals to the inner lining, the endothelium, of blood vessels.
This impaired endothelial function is a marker for increased risk of cardiovascular disease.
Dr Malte Kelm from the Heinrich-Heine-University in Duesseldorf and his team recruited 12 healthy smokers in their early 30s for their double-blind, crossover study.
On the first day they were given either a cocoa drink made by Mars that is specially enriched in flavanols or a drink that tasted the same, but contained very low levels of flavanols, and then crossed over on the second day.
Circulating nitric oxide levels and blood vessel responses (or the flow-mediated dilation) were measured before drinking the cocoa and again two hours later.
There were significant increases in circulating nitric oxide and flow-mediated dilation after ingestion of drinks containing 176 to 185 milligrams of flavanols, a dose potentially exerting maximal effects. These changes correlated with increases in flavanol metabolites.
In addition, the improvements were reversed when the participants were given a drug (L-NMMA) that interferes with nitric oxide signaling, thus supporting the idea that the flavanol-rich cocoa drink produced its effects by influencing the nitric oxide system.
"Taken together, these findings support the notion that flavanol-rich foods, including cocoa products, may help to promote cardiovascular health," Dr Kelm said.
The small study needs to be confirmed by further research, however, before consumers can be advised to consume high amounts of flavanols for heart health.
It is still not known, for example, whether or not the chronic consumption of flavanol-rich foods can lead to sustained increases in endothelial function, and the prevention of future cardiovascular events.
Lead author Christian Heiss added that in smokers, it is unlikely that cocoa can completely attenuate the deleterious effects.
However Mary B. Engler, based at the University of California in San Francisco, noted that the study has helped to identify the optimal concentrations, potential mechanisms and the role of biologically active metabolites of the cocoa flavonoids in the improvement in vascular function in smokers.