Effect of cocoa on blood pressure.
Level 1 - systematic review of randomized trials
Systematic review and meta-analysis of randomized controlled trials
PubMed 28439881 · doi:10.1002/14651858.CD008893.pub3
What was done
Authors updated a Cochrane systematic review searching databases through November 2016 for randomized controlled trials lasting at least two weeks that evaluated flavanol-rich chocolate or cocoa products versus low-flavanol products or placebo in adults with or without hypertension. Random-effects meta-analyses measured differences in systolic blood pressure (SBP) and diastolic blood pressure (DBP). Subgroup and sensitivity analyses evaluated baseline blood pressure, flavanol content in controls, age, study duration, blinding, and industry employment.
What was found
Thirty-five trials (40 treatment comparisons, 1804 mainly healthy participants; duration 2 to 18 weeks, mean 9 weeks) were analyzed. Active cocoa interventions provided 30 to 1218 mg flavanols per day (mean 670 mg). Cocoa significantly lowered SBP (mean difference -1.76 mmHg, 95% CI -3.09 to -0.43, P = 0.009; 40 comparisons, 1804 participants) and DBP (mean difference -1.76 mmHg, 95% CI -2.57 to -0.94, P < 0.001; 39 comparisons, 1772 participants). SBP was reduced by 4 mmHg in hypertensive participants (9 comparisons, 401 participants), trended lower in prehypertensive participants (8 comparisons, 340 participants), and did not change significantly in normotensive participants (23 comparisons, 1063 participants; subgroup difference P = 0.08, I2 = 60%). Adverse events, primarily gastrointestinal symptoms and nausea, occurred in 1% of cocoa participants versus 0.4% of control participants.
Why it matters
Flavanol-rich cocoa intake provides a small, statistically significant short-term reduction in blood pressure, with potentially greater benefits in individuals with hypertension.
Limits
Trial durations were short (mean 9 weeks, maximum 18 weeks), leaving long-term efficacy, safety, and cardiovascular clinical outcomes unmeasured. High unexplained heterogeneity between trials led to downgrading evidence quality from high to moderate. Subgroup analysis by baseline blood pressure showed only borderline statistical significance. Sensitivity analysis excluding trials with industry-employed authors (33 trials, 1482 participants) showed a slight reduction in effect size.
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