Does chocolate reduce blood pressure? A meta-analysis
Ried et al. BMC Medicine 2010, 8:39
Karin Ried1*, Thomas Sullivan2, Peter Fakler1, Oliver R Frank1, Nigel P Stocks1
Background: Dark chocolate and flavanol-rich cocoa products have attracted interest as an alternative treatment
option for hypertension, a known risk factor for cardiovascular disease. Previous meta-analyses concluded that
cocoa-rich foods may reduce blood pressure. Recently, several additional trials have been conducted with
conflicting results. Our study summarises current evidence on the effect of flavanol-rich cocoa products on blood
pressure in hypertensive and normotensive individuals.
Methods: We searched Medline, Cochrane and international trial registries between 1955 and 2009 for randomised
controlled trials investigating the effect of cocoa as food or drink compared with placebo on systolic and diastolic
blood pressure (SBP/DBP) for a minimum duration of 2 weeks. We conducted random effects meta-analysis of all
studies fitting the inclusion criteria, as well as subgroup analysis by baseline blood pressure (hypertensive/
normotensive). Meta-regression analysis explored the association between type of treatment, dosage, duration or
baseline blood pressure and blood pressure outcome. Statistical significance was set at P < 0.05.
Results: Fifteen trial arms of 13 assessed studies met the inclusion criteria. Pooled meta-analysis of all trials
revealed a significant blood pressure-reducing effect of cocoa-chocolate compared with control (mean BP change
± SE: SBP: -3.2 ± 1.9 mmHg, P = 0.001; DBP: -2.0 ± 1.3 mmHg, P = 0.003). However, subgroup meta-analysis was
significant only for the hypertensive or prehypertensive subgroups (SBP: -5.0 ± 3.0 mmHg; P = 0.0009; DBP: -2.7 ±
2.2 mm Hg, P = 0.01), while BP was not significantly reduced in the normotensive subgroups (SBP: -1.6 ± 2.3
mmHg, P = 0.17; DBP: -1.3 ± 1.6 mmHg, P = 0.12). Nine trials used chocolate containing 50% to 70% cocoa
compared with white chocolate or other cocoa-free controls, while six trials compared high- with low-flavanol
cocoa products. Daily flavanol dosages ranged from 30 mg to 1000 mg in the active treatment groups, and
interventions ran for 2 to 18 weeks. Meta-regression analysis found study design and type of control to be
borderline significant but possibly indirect predictors for blood pressure outcome.
Conclusion: Our meta-analysis suggests that dark chocolate is superior to placebo in reducing systolic
hypertension or diastolic prehypertension. Flavanol-rich chocolate did not significantly reduce mean blood pressure
below 140 mmHg systolic or 80 mmHg diastolic.