Pulling data from 20 studies published over the last decade, researchers found that people who ate flavanol-rich cocoa products every day for a few weeks saw their blood pressure drop by about two or three points.
That doesn't mean people should drop exercise in favor of chocolate, said Dr. Elizabeth Jackson, a cardiologist and assistant professor of medicine at the University of Michigan Health Systems in Ann Arbor.
"If I had to choose between cocoa and exercise, I would take the exercise," said Jackson, who was not involved in the new study.
"To me this says a little bit of dark chocolate isn't too bad, but you wouldn't want to go overboard with the calories and eat a pound of chocolate," she said.
For the analysis, published in The Cochrane Library, Australian researchers searched several online databases to find randomized controlled trials - considered the "gold standard" of medical research - that compared people eating flavanol-rich cocoa products to people eating low-flavanol cocoa powder or products that contained none of the plant compounds.
While the researchers cannot say flavanols are responsible for lowering blood pressure in the study participants, the compounds - which are also found in foods such as green tea, berries and red wine - are linked to nitric oxide production in the body. Nitric oxide, according to the authors, helps relax blood vessels, which reduces blood pressure.
According to the American Heart Association, a person's systolic blood pressure (the top number) should be less than 120 millimeters of mercury (mm Hg), and their diastolic blood pressure (the bottom number) should be less than 80 mm Hg.
The 20 studies included in the review followed people who were generally healthy for two to 18 weeks.
Of 856 participants, 429 ate between 3 grams (g) and 100 g of dark chocolate or cocoa that contained anywhere from 30 milligrams (mg) to 1080 mg of flavanols, daily.
The other 427 people were put in comparison groups that ate low-flavanol cocoa powder or products that did not contain any flavanols.
At the end of the studies, those who ate the flavanol-rich dark chocolate or cocoa product saw their systolic blood pressure fall by roughly 2.8 mm Hg while their diastolic fell by 2.2 mm Hg.
There are, however, some limitations to the findings.
Since most of the studies included in the analysis only followed people over a few weeks, the researchers cannot say what, if anything, would happen to the blood pressure of a person who ate cocoa or chocolate over months or years.
They also can't say if eating cocoa or dark chocolate led study participants to have fewer heart attacks or strokes, both of which are linked to high blood pressure.
In addition, there's no telling how much cocoa or chocolate would be best, because each study used different amounts. Moreover, not all cocoa is equivalent because processing can remove flavanols from the finished product.
The effects also seemed greater in younger people compared to older adults.
Jackson said that's not surprising since blood vessels may become less elastic as people age, and would be less likely to react to the nitric oxide.
The studies were also of varying quality, and overall the researchers said the quality of the evidence was low.
Still, the study's lead author Dr. Karin Ried of the National Institute of Integrative Medicine in Melbourne, Australia, told Reuters Health there may be a place for a bit of daily chocolate in a healthy lifestyle.
"Moderate regular dosages of flavanol-rich cocoa products such as dark chocolate may be part of a comprehensive lifestyle plan to optimizing health," Ried said in an email.
SOURCE: http://bit.ly/MvDtGQ The Cochrane Library, online August 14, 2012.