Flavonols are found naturally in chocolate, fruit, red wine and teas, and have previously been linked to improvements in heart health.
The new study, sponsored by confectionary giant Mars, examined the effect on blood vessel relaxation of chocolate flavanols in the form of a specially prepared cocoa drink, and then a drink containing isolated, cocoa-derived (-)epicatechin.
"Applying accepted causality criteria and gold standard methodologies, we have been able to advance our understanding of the relationship between the intake of certain flavanols present in cocoa, their absorption into the circulation, and their effects on cardiovascular function," said lead author Hagen Schroeter, from the University of California, Davis.
The initial randomised, double-blind, cross-over study gave volunteers a specially prepared cocoa drink containing either high or low concentrations of specific cocoa flavanols. Only the group that consumed the flavanol rich drink showed blood vessel relaxation.
A follow-on "proof-of-concept" study gave volunteers either a placebo drink or a drink containing isolated, cocoa-derived (-)epicatechin. The latter test group experienced similar blood vessel relaxation as for the flavanol-rich cocoa drink.
The role of (-)epicatechin was directly linked to nitric oxide, a molecule used by the endothelium to signal surrounding muscle to relax, thereby dilating the blood vessels and increasing blood flow. This supports previous research by individual team members suggesting a link between nitric oxide and cocoa flavanols.
"Pinpointing specific nutrients responsible for the observed cardiovascular effects, as we are seeing here with (-)epicatechin, opens up new possibilities for the development of dietary interventions for cardiovascular disease," said co-author Norman Hollenberg from Harvard Medical School.
Mars has been very active in this research area, having spent over 15 years researching the benefits of cocoa. Previous research by members of the international team has benefited from Mars sponsorship, and a mounting body of supporting evidence has strengthened the link between flavanols and nitric oxide.
The message is not to eat vast quantities of chocolate however. "This new research emphasizes the importance of understanding the potential public health applications of emerging cocoa science," said Harold Schmitz, chief science officer of Mars, and co-author of the study.
Indeed, Professor Ian McDonald from Nottingham University, recently told NutraIngredients.com: "The message must not get out there that all chocolate products have these benefits. It would be a more sensible strategy to develop low-fat, low-energy drinks that are enriched in these flavanols."
The study is published in the Proceedings of the National Academy of Sciences of the United States of America (Vol. 103, pp. 1024-1029).