The findings appear in Hypertension's August issue.
High Blood Pressure Is Common
A quick, noninvasive test can check blood pressure.
The study included 10 men and 10 women with high blood pressure that had never been treated. They were recruited from a clinic at Italy's Università di L'Aquila.
Subjects were about 43 years old, on average. To qualify, they needed systolic blood pressure (the first number of a blood pressure reading) of 140-159 or diastolic blood pressure (the second number) of 90-99.
Participants didn't have other health problems. They also didn't smoke or drink alcohol.
Eating Chocolate for Science's Sake
The study wasn't a chocolate free-for-all. The researchers drew up a schedule detailing the type and amount.
First, chocolate was totally forbidden for a week. Next, subjects were given a daily bar (about 3.5 ounces) of dark or white chocolate for another week.
Then, chocolate was banned for another week. Finally, subjects tried whichever bar they hadn't already eaten for a week.
Meanwhile, they wore mobile blood pressure monitors 24 hours a day.
Subjects were also told to maintain their normal activity level and to budget their diet for chocolate's calories.
With dark chocolate, 24-hour systolic blood pressure dropped 12 points; diastolic blood pressure dipped 8.5 points.
No benefits were seen with white chocolate.
Dark Chocolate Stood Out
White chocolate was the perfect comparison food, states researcher Jeffrey Blumberg, PhD, in a news release.
White chocolate doesn't contain any flavonoids. But it has all the other ingredients and calories of dark chocolate, says Blumberg.
"It's important to note that the dark chocolate we used had a high level of flavonoids, giving it a slightly bittersweet taste," he says.
"Most Americans eat milk chocolate, which has a low amount of these compounds," continues Blumberg.
Milk chocolate wasn't tested in the study.
Blumberg is a senior scientist, associate director, and chief of the Antioxidants Research Laboratory at the Jean Mayer USDA Human Nutrition Research Center on Aging. The Center is located at Tufts University.
More Work Ahead
The study was small and the findings need to be confirmed, write Blumberg and colleagues.
They didn't compare dark chocolate to other flavonoid-rich fare.
"Caution is always warranted when considering dietary recommendations for foods high in fat and calories, especially for [heart] disease," write the researchers.