Potential Heart Health Benefits of Cocoa Polyphenols
Prof. Norman K. Hollenberg, MD, PhD
The proper place of any element in the diet can only be understood in the context
of our overall thoughts on the subject of nutrition. Concerns about adequacy
of nutrition, and concepts of what represents an optimal diet have evolved
continuously over the past century. Early in the twentieth century, major
emphasis was given to deficits, ranging from vitamin deficiencies to frank
starvation. Beginning at about the middle of the twentieth century, a
progressive rise in the frequency and severity of obesity has become the
subject of a widespread, sustained, and appropriate concern. As a by-product
of that concern, there seems to be a knee-jerk response to thoughts about
chocolate intake: In a world in which obesity is rampant, who needs yet
another source, albeit a pleasurable one, of 'empty calories'? This question
raises two additional questions. Does chocolate intake actually make a
substantial contribution to obesity? Do chocolate and cocoa provide only
empty calories? The answer to both questions is encouraging.
Does chocolate intake lead to obesity? It is instructive to compare countries
in which chocolate use is very high with countries that consume a much more
limited per capita chocolate intake. The countries with the two highest levels
of chocolate intake, Switzerland and Norway, are not commonly associated with
obesity. One the other hand, the U.S.A. and Finland have a chocolate intake
about a third of that found in Norway and Switzerland, and in both obesity is
rampant.
What about the issue of empty calories? There is growing evidence that at least
some chocolate and cocoa might offer substantial health benefits. Again, that
information must be viewed in the broader context. We live in a world in which
the notion of the health benefits of antioxidants, and the potential benefits
of specific items in the diet such as red wine and green tea appear in the
newspapers almost daily. In November 1999, one of the most conservative general
magazines in the world, Consumer Reports, featured an article on the health
benefits of green tea. Indeed, the article included a table which ranked the
various green teas for their health benefits!
There is a hierarchy in the quality of evidence available on any health subject.
The best evidence comes from large, carefully controlled, randomized clinical
trials. Evidence from smaller trials, designed in the same way, stands second.
Evidence from observational studies, from epidemiology, stands a distant third:
At best, only an association can be found. Studies on mechanisms, if they concur
with the epidemiological evidence, increase the likelihood that the association
is real. Far behind comes evidence from uncontrolled trials, case reports, and
anecdotes. It is sobering that the best available evidence in this area, whether
the subject be red wine, green tea, or antioxidants, comes from ‘evidence of the
third class' association, perhaps supplemented by pathophysiological, mechanistic
considerations. Indeed, when we consider vitamin E, the epidemiological evidence
remains supportive whereas the well-designed, well-controlled clinical trials
have largely been negative.
The positive properties of red wine, green tea, and many fruits is widely
considered to involve an antioxidant class of polyphenols, which in addition
to their antioxidant properties have a range of pharmacological properties that
could have health benefits. These benefits include a salutary action on platelets
and blood vessels. Evidence to be presented at this symposium includes the fact
that polyphenol-rich cocoa and chocolate lead to measurable plasma levels of the
potentially useful agents; at the concentration in vitroand in vivo, there is
a useful influence on platelet function that matches the influence of aspirin;
that in vitro cocoa polyphenols activate nitric oxide synthesis which is an
important element in the endothelial function. Endothelial dysfunction is
characterises atherosclerosis, hypertension, and diabetes mellitus.
Although the evidence is still preliminary, it is worthwhile and constructive
to consider the fact that the evidence suggesting a health benefit of cocoa
and chocolate is at least comparable to the level of evidence supporting positive
health effects of green tea and red wine.
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