Researchers from the University of Adelaide (Australia) searched Medline, the Cochrane database, and international trial registries for randomized controlled trials held between 1955 and 2009 investigating the effect of flavanol-rich cocoa as food or drink on systolic blood pressure (SBP) and diastolic blood pressure (DBP), for a minimum duration of two weeks. A meta-analysis of the 15 trial arms of the 13 assessed studies fitting the inclusion criteria was conducted, as well as subgroup analysis by baseline BP (hypertensive or normotensive), to explore the association between type of treatment, dosage, duration or baseline BP, and BP outcome.

The results showed that daily flavanol dosages ranged from 30 mg to 1,000 mg in the active treatment groups, and interventions ran for 2 to 18 weeks. The pooled meta-analysis of all trials revealed that for people with hypertension, eating chocolate could reduce their BP by up to 5%, when compared with control; a subgroup meta-analysis, however, revealed that chocolate consumption was significant only for the hypertensive or pre-hypertensive subgroups, as BP was not significantly reduced in the normotensive subgroups. The study was published on June 28, 2010, in the open access journal BMC Medicine.

"Flavanols have been shown to increase the formation of endothelial nitric oxide, which promotes vasodilation and consequently may lower blood pressure,” sad lead author Karin Ried, Ph.D., manager of the Queensland (Australia) Primary Health Care Research Evaluation and Development (PHCRED) project. "There have, however, been conflicting results as to the real-life effects of eating chocolate. We've found that consumption can significantly, albeit modestly, reduce blood pressure for people with high blood pressure but not for people with normal blood pressure.”

Flavonoids are a larger family of compounds found in the seeds and skins of plants, such as grapes, cocoa beans, and citrus fruits. Other studies with flavonoid-containing foods, such as tea and wine, have shown similar effects on vascular and blood pressure regulation, as well as improving insulin sensitivity and reducing one of the major risk factors for diabetes.

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