Cardiovascular Showdown—Chocolate vs. Coffee

Chocolate and coffee seem to go together perfectly. Think of a double-shot mocha at the corner coffee shop. Yet, the two ingredients appear to have opposite effects on a person’s arteries, according to two new studies. Chocolate is good for them, whereas coffee—or at least its caffeine—does damage.

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: Chocolate Hearts). 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?

Janet Raloff is the Editor, Digital of Science News Explores, a daily online magazine for middle school students. She started at Science News in 1977 as the environment and policy writer, specializing in toxicology. To her never-ending surprise, her daughter became a toxicologist.

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