Some "chocoholics" who just couldn't give up their
favorite treat to comply with a study to test blood
stickiness have inadvertently done their fellow chocolate
lovers — and science — a big favor.
Their "offense," say researchers at Johns Hopkins, led
to what is believed to be the first biochemical analysis to
explain why just a few squares of chocolate a day can
almost halve the risk of heart attack death in some men and
women by decreasing the tendency of platelets to clot in
narrow blood vessels.
"What these chocolate 'offenders' taught us is that
the chemical in cocoa beans has a biochemical effect
similar to aspirin in reducing platelet clumping, which can
be fatal if a clot forms and blocks a blood vessel, causing
a heart attack," said Diane Becker, a professor at the
schools of Medicine and Public Health.
Becker cautions that her work is not intended as a
prescription to gobble up large amounts of chocolate candy,
which often contains diet-busting amounts of sugar, butter
and cream. But as little as 2 tablespoons a day of dark
chocolate — the purest form of the candy, made from
the dried extract of roasted cocoa beans — may be
just what the doctor ordered.
Researchers have known for nearly two decades that
dark chocolate, rich in chemicals called flavonoids, lowers
blood pressure and has other beneficial effects on blood
flow. The latest Johns Hopkins findings, presented Nov. 14
at the American Heart Association's annual Scientific
Sessions in Chicago, identified the effect of normal
everyday doses of chocolate found in ordinary foods, unlike
previous studies that found decreased platelet activity
only at impractically high doses of flavonoids equivalent
to eating several pounds of chocolate a day.
In the study, 139 people — whom Becker somewhat
tongue-in-cheek calls "chocolate offenders" — were
disqualified from a much larger study looking at the
effects of aspirin on blood platelets. The Genetic Study of
Aspirin Responsiveness, known as GeneSTAR, was conducted at
Johns Hopkins from June 2004 to November 2005 and enrolled
more than 500 men and 700 women participants nationwide.
Shortly before aspirin dosing began for the subjects,
they were told to stay on a strict regimen of exercise and
to refrain from smoking or using foods and drinks known to
affect platelet activity. These included caffeinated
drinks, wine, grapefruit juice — and chocolate.
The noncompliers who admitted to eating chocolate were
a diverse group who got their flavonoid "fix" from a
variety of sources, including chocolate bars, cups of hot
cocoa, grapes, black or green tea and strawberries. And
while they were excluded from the aspirin study, Becker and
her team scoured their blood results for chocolate's effect
on blood platelets, which the body recycles on a daily
When platelet samples from both groups were run
through a mechanical blood vessel system designed to time
how long it takes for the platelets to clump together in a
hair-thin plastic tube, the chocolate lovers were found to
be less reactive, on average taking 130 seconds to occlude
the system; platelets from those who stayed away from
chocolate as instructed clotted faster, at 123 seconds.
In another key test, of urine for waste products of
platelet activity, primarily urinary thromboxane
(11-dehydro-thromboxane B2), scientists found that
chocolate eaters showed less activity and waste products on
average, at 177 nanograms per millimol of creatinine, vs.
an average of 287 nanograms per millimol of creatinine in
the group that abstained.
Participants ranged in age from 21 to 80; 31 percent
were black and the rest white. In total, more than 200
different tests of platelet reactivity were performed and
analyzed in the study. Because whole blood contains other
cells that affect platelet aggregation, testing was
repeated using a purified version of test samples made up
of strictly platelet-rich plasma.
None of the "offenders" had previous histories of
heart problems, such as a heart attack, but all were
considered to be at slightly increased risk of heart
disease because of family history. Fifty percent of women
participants were postmenopausal.
"These results really bring home the point that a
modest dietary practice can have a huge impact on blood and
potentially on the health of people at a mildly elevated
risk of heart disease," said co-author Nauder Faraday, an
associate professor in the School of Medicine. "But we have
to be careful to emphasize that one single healthy dietary
practice cannot be taken alone but must be balanced with
exercise and other healthy lifestyle practices that impact