One small square of dark chocolate a day could have a clinically relevant effect on blood pressure, according to a preliminary trial from Germany. People aged 56-74 who ate 6.3 g of dark chocolate for 18 weeks dropped their systolic blood pressure nearly 3 mm Hg more than those given a matching portion of white chocolate (−2.9 mm Hg, 95% CI −3.9 to −2.0). The dark chocolate, which contained 30 mg of polyphenols, reduced diastolic blood pressure by a mean of 1.9 mm Hg (1.1 to 2.7).
The researchers think a specific subgroup of polyphenols called flavanols are probably responsible, mediated by the vasodilator S-nitrosoglutathione. At the end of the trial, serum concentrations of S-nitrosoglutathione were significantly higher in the group given dark chocolate.
The 44 participants had baseline blood pressures between 130/85 and 160/100. They were healthy, reasonably affluent non-smokers with normal body weight and a habitually low intake of alcohol and chocolate. Dark chocolate won't necessarily work the same way in other populations, say the authors. But these findings pave the way for bigger, longer, and more diverse studies, preferably looking for the effects of cocoa flavanols on heart disease.