Phytochemicals known as flavanols, which are found in chocolate,
fruits and vegetables, can boost the levels of nitric oxide
in the blood of smokers and reverse some of their smoking-related
impairment in blood vessel function, according to a new study
in the Oct. 4, 2005, issue of the Journal of the American College
"While the long-term benefits of such improvements remain
to be established, we believe that one exciting outcome of this
study is the demonstration that flavanol-rich cocoa can significantly
improve an important marker of cardiovascular health in a population
with an established cardiovascular risk factor. This raises
the possibility that a potential new agent for the prevention
and/or treatment of cardiovascular disease may emerge from additional
research," said Malte Kelm, M.D. from the Heinrich-Heine-University
in Duesseldorf, Germany.
The researchers studied smokers because their 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.
A dozen smokers (six men and six women) in their early 30s,
who did not have any known health problems, were enrolled in
the double-blind crossover study to compare the effects of a
cocoa drink rich in flavanols to a cocoa drink that tasted the
same, but contained very low levels of flavanols. One woman
was excluded from the analysis because she had high cholesterol
levels. Circulating nitric oxide levels and blood vessel responses
(flow-mediated dilation) were measured before drinking the cocoa
and again two hours later. Each participant drank flavanol-rich
and flavanol-poor cocoa drinks during different testing sessions.
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.
However, he said the main point of the study was to identify
the active ingredients so that they can be studied further.
The researchers pointed out that the cocoa drink they used was
specially processed to retain much higher levels of flavanols
than are typically found in commercially-available cocoa drinks;
so it is unlikely that drinking more hot chocolate would produce
a similar effect.
Even though this study involved only 11 participants, lead
author Christian Heiss, M.D., Ph.D., pointed out that the results
were in agreement with other studies indicating potential benefits
from flavanol-rich foods, including cocoa and chocolate.
"Therefore, we feel that there exists an increasing body of
evidence for an acute effect of flavanol-rich foods on vascular
reactivity. Nevertheless, the conclusion drawn from these results
have to be interpreted with caution, because it is not known
whether or not the chronic consumption of flavanol-rich foods
leads to sustained increases in endothelial function, and the
prevention of future cardiovascular events. In particular in
smokers, it is unlikely that cocoa can completely attenuate
the deleterious effects of continued smoking," Dr. Heiss said.
Dr. Heiss is currently affiliated with the Division of Cardiology,
University of California in San Francisco, California.
The researchers emphasized that this study was not designed
to investigate whether flavanols could protect smokers; smokers
were enrolled because they tend to have abnormal blood vessel
Mary B. Engler, Ph.D., who is also at the University of California
in San Francisco, but was not connected with this study, noted
that it is the first such study in smokers to demonstrate that
endothelial function improved after drinking cocoa with high
levels of flavonoids.
"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. Although, it is a small study with 11 subjects,
it has important implications and further supports the current
evidence on the heart-healthy benefits of dark chocolate and
drinks rich in cocoa flavonoids. Larger, long-term studies are
definitely needed in follow-up," Dr. Engler said.
Dr. Engler emphasized that quitting smoking is the best way
to reduce heart disease risk. She also pointed out that many
foods and beverages contain a substantial amount of the same
flavonoids (flavanols-epicatechin, catechin) found in cocoa
and dark chocolate. These foods include green and black tea
(especially Ceylon tea), red wine, sweet cherries, apples, apricots,
purple grapes, blackberries, raspberries and broad beans.
Professor Gerd Heusch, M.D., at the Universitätsklinikum Essen
in Essen, Germany, who also was not connected to this research
effort, said the study indicates that flavonoids have an effect
on the same nitric oxide system that is damaged by smoking.
"A flavanol- rich drink is capable of increasing nitric oxide
levels in the blood and reversing the detrimental effect of
smoking on vascular adaptation. It remains to be seen whether
the acute beneficial effect of a flavanol-rich drink translates
into a long-term benefit, in terms of attenuating or preventing
the development of atherosclerosis," Dr. Heusch said.
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