In order to prove that the blood pressure reduction is linked to the consumption of dark chocolate, the scientists conducted a trial between January 2005 and December 2006.

The test group included 44 adults (age 56 through 73 years; 24 women, 20 men) with untreated upper-range prehypertension (BP 130/85 – 139/89) or stage 1 hypertension (BP 140/90 – 160/100).

The volunteers received for 18 weeks either 6.3 g (30 calories) per day of dark chocolate containing 30 mg polyphenols or matching polyphenol-free white chocolate.

The researchers found that systolic blood pressure, the top number, fell an average of nearly three points and diastolic dropped almost two points in the dark chocolate group, compared with no change in blood pressure readings in the white chocolate group. Also, hypertension prevalence declined from 86 percent to 68 percent.

“Although the magnitude of the BP reduction was small, the effects are clinically noteworthy. On a population basis, it has been estimated that a 3-mm Hg reduction in systolic BP would reduce the relative risk of stroke mortality by 8 percent, of coronary artery disease mortality by 5 percent, and of all-cause mortality by 4 percent,” the authors write.

In the United States, more than 65 million adults have high blood pressure levels above 140/90, according to the National Heart, Lung and Blood Institute. An estimated 59 million more have pre-hypertension, which means blood pressure of 120/80 or above.

Adoption of small amounts of flavanol-rich cocoa into the habitual diet is a dietary modification that is easy to adhere to and therefore may be a promising behavioral approach to lower blood pressure in individuals with above-optimal blood pressure. Still, as the authors noted longer term studies are needed to evaluate the effects of dark chocolate in other, larger populations.