Researchers have suspected for many years that chocolate may have a beneficial effect on blood pressure, ever since discovering that the indigenous Kuna people of the Central American island San Blas have normal blood pressure well into old age. One of the major lifestyle differences between the traditional Kuna and their urban relatives, scientists found, is that the traditional Kuna drink enormous quantities of essentially unprocessed cocoa.
Laboratory studies later confirmed that a group of naturally occurring chocolate chemicals called flavanols may have a beneficial effect on blood pressure. Scientists believe that flavanols cause nitric oxide to form in the body, which in turn relaxes and opens the blood vessels.
But until recently, there has been little experimental evidence to suggest that benefit can be gained simply from eating the processed chocolate sold in the United States.
Then in August 2012, researchers from the National Institute of Integrative Medicine in Melbourne, Australia and the University of Adelaide published a research review in The Cochrane Library finding that people who consumed more chocolate or cocoa really do have lower blood pressure.
The researchers reviewed the results of 20 separate studies involving a total of 856 people who were fed between three and 100 grams of chocolate or cocoa powder each day, containing between 30 and 1,080 mg of total flavanols. All the studies lasted between two and eight weeks, except for one that lasted 18 weeks.
On average, participants who consumed the chocolate lowered their blood pressure by two to three mmHg compared with participants given placebos. In trials where the placebo group consisted of people fed flavanol-free chocolate, the relative blood pressure decrease in the experimental group was even greater (three to four mmHg).
"Although we don't yet have evidence for any sustained decrease in blood pressure, the small reduction we saw over the short term might complement other treatment options and might contribute to reducing the risk of cardiovascular disease," lead researcher Karin Ried said.
Large observational study
Further evidence comes from a large longitudinal study conducted by researchers from the German Institute of Human Nutrition and published in the European Heart Journal in March 2010. Researchers collected dietary information on 19,357 people, all of whom were between the ages of 35 and 65, had no history of heart attack or stroke and were not taking blood pressure drugs. They found that patients who consumed the most chocolate (an average of 7.5 grams per day) had blood pressure about one mmHg lower than participants who ate the least (an average of 1.7 grams per day).
In the eight years following the study, the researchers found that participants who had the most chocolate were significantly less likely to suffer from heart attacks or strokes, and that differences in blood pressure accounted for 12 percent of this risk.
"Chocolate consumption appears to lower cardiovascular disease risk, in part through reducing blood pressure," the researchers wrote.
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