Previous research has shown that eating chocolate can lower blood pressure, but doctors have worried that any benefit could be offset by high doses of sugar, fat and calories.
The study conducted by German researchers at the University of Cologne sought to examine the effect of consuming small amounts of dark chocolate -- which has lower levels of sugar and fat, said the study appearing in the July 4 issue of the Journal of the American Medical Association (JAMA).
A clinical trial carried out between January 2005 and December 2006 showed that 6.3 grams (30 calories) of dark chocolate a day was associated with a small but significant lowering of blood pressure, the study said.
The trial was carried out on 44 adults from 56 to 73 years old, including 24 women and 20 men, who suffered from pre-hypertension or stage one hypertension.
Participants were randomly assigned over 18 weeks to eat either dark chocolate containing 30 milligrams of healthy polyphenols or white chocolate, which has no cocoa.
For those who ate dark chocolate, their average systolic blood pressure was lowered by 2.9 millimeters of mercury and diastolic blood pressure by 1.9 millimeters without a change in body weight, plasma levels of lipids or glucose, the study said. Systolic refers to the top reading for blood pressure, and diastolic the bottom reading.
Consuming dark chocolate also helped reduce the prevalence of hypertension, or high blood pressure, from 86 percent to 68 percent, it said.
The participants who ate white chocolate saw no reduction in their blood pressure.
While eating dark chocolate resulted in a relatively small reduction in blood pressure, "the effects are clinically noteworthy," the study said.
For a population, a three millimeter reduction in systolic blood pressure would reduce the relative risk of stroke deaths by eight percent and the risk of coronary artery disease by five percent, the authors wrote.
The results of the trial were "intriguing," the study said, as having heart patients eat small amounts of dark chocolate would be much simpler than the conventional approach which requires patients to change their entire diet.
Eating dark chocolate "is a dietary modification that is easy to adhere to and therefore may be a promising behavioral approach to lower blood pressure," the authors wrote.
The researchers said future studies should examine the effects of dark chocolate in other populations and look at results over a longer period.