A new meta-analysis of studies investigating the effect of dark chocolate and flavanols on hypertension has drawn mixed conclusion and suggest more studies be done on dietary habits and genetic factors.
Dark chocolate containing high levels of cocoa solids and flavanol-rich cocoa products have attracted interest for their potential to reduce high blood pressure for some time. A number of chocolate companies have been exploring the potential, including Barry Callebaut and Mars who recently teamed up to develop a system for measuring antioxidant activity and boost consumer awareness.
Previous meta-analyses of research studies have drawn positive conclusions, but the authors of the new paper, from the University of Adelaide in Australia, saw value in a new review to take into account conflicting results from recent intervention trials.
They searched for randomised controlled trials conducted between 1955 and 2009 which investigated the effects of cocoa as a food or drink on systolic and diastolic blood pressure in hypertensive individuals or those with normal blood pressure (normotensive) for at least 2 weeks.
Altogether 15 trial arms of 13 studies were identified as meeting the inclusion criteria.
Nine trials used chocolate with 50 to 70 per cent chocolate, and compared the effects with white chocolate or coca-free controls. Six compared high and low flavanol cocoa products. Flavanol doses ranged from 30mg to 1000mg a day.
While the pooled data did show a significant blood-pressure reducing effect of cocoa-chocolate compared to the control, this was only seen to be the case in hypertensive and pre-hypertensive subgroups – not in normotensive subgroups.
Dark chocolate was seen to perform better than a placebo at reducing systolic or diastolic pre-tension, but flavonol-rich chocolate did not significantly reduce blood pressure below 140mmHg systolic or 80mmHg diastolic.
“Additional trials of hypertensive populations are needed to elucidate whether local dietary habits or genetic factors influence the blood pressure-lowering effect of cocoa,” they concluded.
The meta analysis has been published in the open access journal BMC Medicine, and is available at http://www.biomedcentral.com/content/pdf/1741-7015-8-39.pdf
Does chocolate reduce blood-pressure? A meta-analysis
Authors: Reid, K., Sullivan, T., Falkler, P., Frank, O., Stocks, N