Does chocolate reduce blood pressure? A meta-analysis

Karin Ried, Thomas Sullivan, Peter Fakler, Oliver R Frank, Nigel P Stocks, Karin Ried, Thomas Sullivan, Peter Fakler, Oliver R Frank, Nigel P Stocks

Abstract

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.

Figures

Figure 1
Figure 1
Flow diagram of trial selection.
Figure 2
Figure 2
Meta-analysis of the effect of chocolate/cocoa on (A) systolic blood pressure or (B) diastolic blood pressure. N, number of participants; ΔSBP/ΔDBP, difference in mean SBP/DBP between start and end of intervention; SD, standard deviation; CI, confidence interval
Figure 3
Figure 3
Subgroup meta-analysis of the effect of chocolate/cocoa on (A) systolic blood pressure of hypertensive subjects (≥ 140 mmHg at baseline) or (B) 'normotensive' subjects (< 140 mmHg at baseline) and on (C) diastolic blood pressure of (pre-)hypertensive subjects (≥ 80 mmHg) or (D) 'normotensive' subjects (< 80 mmHg). See Figure 2 legend for abbreviation definitions.
Figure 4
Figure 4
Funnel plots of trials included in the meta-analysis for (A) systolic blood pressure and (B) diastolic blood pressure. The vertical line of Begg's funnel plot represents the pooled mean effect size, and the dotted lines represent the 95% confidence interval. P values are derived from Egger's test.

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