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June 5, 2004
Two
teams of cardiologists from Greece presented the findings
last week in New York
City at the American Society of Hypertension's
annual meeting.
Both studies were small and brief, so they
aren't conclusive. But the Athens-based researchers told Science
News Online that they're preparing follow-up studies of whether
the effects seen in the initial trials hold up when people
consume coffee or chocolate regularly.
Chocolate says relax
A host of studies have identified beneficial properties in
chocolate's rich supply of cocoa flavonoids — naturally occurring
antioxidants (SN:
3/18/00, p.188:).
In some cases, the flavonoids appear to keep blood platelets
from making the blood too thick and sticky. Other times, they
elevate a person's good cholesterol, the type called high-density
lipoprotein (HDL) cholesterol. Especially impressive, test-tube
studies have shown that the flavonoids from chocolate relax
and dilate blood vessels surgically removed from animals. If
that happens in people, it means chocolate could lower blood
pressure and thus reduce the risk of heart attack and other
heart disease.
In the new study, Charalambos Vlachopoulos of
Athens Medical School and his colleagues at Hippokration Hospital
in fact measured the effect in people eating chocolate.
The
researchers recruited generally healthy men and women around
30 years old to come in for an afternoon of tests after fasting
for 5 hours on each of two separate days. On one day, each
volunteer started by eating a 100-gram (3.5 ounce) bar of chocolate.
It was the bittersweet variety, Vlachopoulos explains, because
dark chocolate has roughly twice the antioxidant punch of milk
chocolate. On the other day, the volunteers received no snack.
For 3 hours on each test day, Vlachopoulos' team monitored
the tension — as stiffness and constriction — of an artery
in each volunteer's arm. To measure stiffness, the scientists
made
a calculation based on people's pulses at their wrists.
For
an indicator of artery constriction, the researchers used an
inflated blood-pressure cuff to cut off blood flow to the forearm
and hand for 4.5 minutes. The return of blood to an artery
triggers the vessel to dilate, boosting blood flow. The researchers
used ultrasound to measure how much the forearm artery responded
when the cuff was removed.
The pulse readings indicated that
people's arteries were definitely less stiff after they ate
the chocolate, Vlachopoulos says. The comparison for artery
dilation also favored chocolate: Volunteers' forearm arteries
were 20 percent more dilated on days of eating chocolate versus
no-chocolate days.
Although the first signs of extra arterial
dilation were evident within an hour after the chocolate snack,
maximum dilation wasn't witnessed until the end of the 3-hour
trial, so it might have gone still higher after measurements
ceased. The delay might have been because the chocolate flavonoids
were absorbed and metabolized by the body slowly.
The ability
of an artery to dilate is choreographed by its lining, or endothelium.
When "endothelial dysfunction" occurs, Vlachopoulos explains,
a cardiologist ends up telling a person, "You have a higher
risk of heart attack, heart failure, or developing hypertension."
Caffeine
turns on tension
"I participated in that study of Dr. Vlachopoulos
and had to eat that big dark chocolate bar. It was so bad.
So bitter," recalls cardiologist Konstantinos Aznaouridis.
As a milk chocolate aficionado, he says that dark chocolate
proved to be more medicine than a treat.
As a coffee lover,
Aznaouridis was inspired to test dilation of the arteries in
people drinking decaf and regular. His team at Athens' Alexandra
Hospital had healthy volunteers drink a cup of coffee containing
no more than 2 milligrams of caffeine or a whopping 80 milligrams
of the stimulant.
The study participants' forearm arteries
dilated significantly more after they drank the decaf, Aznaouridis
reported. Within 90 minutes, their arteries returned to their
original size. However, when these same people drank caffeinated
coffee, their arteries failed to return to normal size during
the study period.
This impaired responsiveness due to caffeine
is worrisome, Aznaouridis notes, since "endothelial dysfunction
is a precursor of atherosclerosis." That's why his next study,
back at Hippokration Hospital, where he now works with Vlachopoulos,
will probe for signs that the body adapts to caffeine in coffee
drinkers studied for 2 weeks. Do people adapt to caffeine,
Aznaouridis asks, or do their arteries suffer as they did in
this brief trial?
References:
Aznaouridis, K., C. Vlachopoulos,
et al. 2004. Dark chocolate improves arterial stiffness and
endothelial function. American Society of Hypertension annual
meeting. May 18-22. New York.
Papamichael, C., K. Aznaouridis,
et al. 2004. Coffee exerts an acute unfavorable effect on
endothelial function of healthy subjects. American Society
of Hypertension
annual meeting. May 18-22. New York.
Further Readings:
Gorman,
J. 2002. More good news about chocolate. Science News 161(March
2):142. Available
to subscribers here.
Harder, B. 2003. Coffee jitters: Caffeine boosts predictor
of heart problems. Science News 163(Jan. 4):5. Available
to subscribers here.
Raloff, J. 2001. Even a little coffee may up heart risk.
Science
News 160(Sept. 22):180. Available to subscribers here.
Chocolate hearts. Science News 157(March 18):188-189.
Available here.
Chocolate therapies (with recipe for Janet's
Chocolate Medicinal Mousse Pie). Science News Online (March
18). Available here.
Eat sweets, live longer. Science News Online
(Dec. 19). Available here.
New heart risk from too much coffee? Science
News 151(Jan. 11):22.
Chocolate: As hearty
as red wine . . . Science News 150(Oct. 12):235.
. . . but we eat it for pleasure. Science News 150(Oct. 12):235.
Prescription-strength chocolate. Science News
Online (Oct. 12). Available here.
Schmitz, H.H. 2002. Flavonoids: What they are and where
you can find them. American Association for the Advancement of
Science annual meeting. Feb. 15. Boston.
Sources:
Konstantinos Aznaouridis Athens Medical
School Hippokration Hospital Vas. Sophias Avenue 114 11528
Athens Greece
Charalambos Vlachopoulos Athens Medical School
Hippokration Hospital Vas. Sophias Avenue 114 11528 Athens
Greece
From
Science News, Vol.
165, No. 23, June 5, 2004
Copyright (c) 2004 Science Service
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