As you probably know is Dr Shock completely biased when writing about chocolate especially dark chocolate. He mostly writes about the research with positive results of chocolate on cardiovascular diseases. A recent review included 5 studies of adequate quality for inclusion in a recent meta analysis as well as 8 other peer reviewed studies for the effect of cocoa on blood pressure.
In these 13 reports dark chocolate lowered blood pressure in 6 of the 7 open label studies but diastolic blood pressure only in 1 of 6 double blind studies and as you know double blind studies are the one’s with the most scientific conclusions. The inconclusive results of all these 13 studies is suggested to be caused by methodological factors of these studies.
the published studies on chocolate and blood pressure include a relatively small number of subjects, and results are conflicting. In addition, because of secrecy surrounding the production of chocolate and the unique sociocultural context of this popular food, research on efficacy and effectiveness is complex.
The lowering of blood pressure mainly appeared in the open label studies, suggesting a placebo effect. Even the double blind studies could have suffered from unblinding due to the bitter taste and physiological effects of flavanoids in chocolate. Different ways of blood pressure measuring methods were used. Especially the double blind studies provided limited detail or used devices with suboptimal accuracy.
Two brands of chocolate were used which seem to differ in chemical and biological properties. Moreover, variations in cocoa bean processing can dramatically alter chemical composition of the final product. Fermentation, roasting, and alkali treatment, while improving flavor, reduce flavanol content. These two brands also purchase cocoa beans from several countries and they blend beans for their products.
So before we can start using dark chocolate as a lifestyle intervention for hypertension and prehypertension some question have to be resolved first. Is it an effect of brand, is their a dose and time dependent effect, what’s the optimal blood pressure measure method?
Until then, take care with dark chocolate
Egan, B., Laken, M., Donovan, J., & Woolson, R. (2010). Does Dark Chocolate Have a Role in the Prevention and Management of Hypertension?: Commentary on the Evidence Hypertension, 55 (6), 1289-1295 DOI: 10.1161/HYPERTENSIONAHA.110.151522