Effects of high flavanol dark chocolate on cardiovascular function and platelet aggregation
Graphical abstract
Introduction
Regular consumption of dark chocolate has been linked to a lower incidence of myocardial infarction and stroke, and to an overall reduction in cardiovascular mortality [1], [2], [3], [4]. Such observations are consistent with reports that cocoa products lower blood pressure [5], [6], [7], [8], improve endothelium-dependent vasodilator responses [7], [8], [9], [10], [11], [12], [13], and inhibit platelet aggregation [12], [13], [14], [15], [16], [17], [18].
The actions of cocoa and dark chocolate have been attributed primarily to the high level of flavan-3-ols. However, the flavanol content of cocoa products is highly variable depending on post-harvest treatment of cocoa beans. Fermentation, drying and roasting reduce total flavanol content, with the result that commercial dark chocolate typically contain < 1% flavanols by weight [19], [20]. Cocoa flavanols are composed of monomers, primarily (−)-epicatechin (10–40% total flavanols), and procyanidins, which are short oligomers composed of epicatechin and catechin units, mainly dimer to decamer (20–80% total flavanols) [19], [20]. Cocoa products also contain high levels of methylxanthines, theobromine (0.5–2.0%) and caffeine (0.03–0.2%) [20], which may act as phosphodiesterase inhibitors or adenosine receptor antagonists [21], [22], [23]. The specific contributions of the flavanol and methylxanthine components to the cardioprotective effects of regular cocoa or dark chocolate consumption have yet to be fully defined.
Patient and volunteer studies of the effects of dark chocolate and cocoa on blood pressure, endothelial function, and platelet aggregation, have often lacked adequate blinding because inappropriate placebo products (such as white chocolate) were used, which lack flavanols and theobromine [5], [6], [7], [9], [12], [14], [15], [16], [17], [18], [24]. Here to investigate the role of flavanols in mediating the actions of dark chocolate on blood pressure and platelet function we compared responses to a high flavanol dark chocolate (HFDC) with a placebo low flavanol dark chocolate (LFDC) in a double-blind crossover study in men with pre-hypertension or mild hypertension.
Section snippets
Study design and participants
The study was a single centre randomized double-blind placebo controlled investigation with a crossover design. Ethical approval for the study was obtained from the NHS Research Ethics Service (East London and the City Research Ethics Committee; REC reference number: 07/Q0605/44). Volunteer participants were recruited through the east London GP network using a database search for men with recently diagnosed untreated mild hypertension (SBP 140–159 mm Hg; DBP 90–99 mm Hg) or prehypertension (SBP
Blood pressure and heart rate changes
The study population was generally middle aged, and mainly pre-hypertensive based on daytime ambulatory blood pressure measurements (Table 2). No significant changes in systolic or diastolic blood pressure were observed after HFDC or LFDC, whether measured by 24 h ambulatory BP recording or in the clinic. There was a tendency for lower SBP and MAP (≈− 2 mm Hg) after HFDC for both overall and daytime ambulatory BP measurements, but this did not reach significance. Heart rate was increased after LFDC
Overview
The age-related increased risk of an atherothrombotic event — myocardial infarction or stroke — is generally viewed as a complex relationship evolving over many years. It is frequently linked to deterioration in vascular function, increased prevalence of proinflammatory changes, raised blood pressure, dyslipidaemia, and platelet thrombogenicity. These are all changes that cocoa flavanols may modulate [1], [2], [3], [4], [5], [6], [7], [8], [9], [10], [11], [12], [13], [14], [15], [16], [17],
Conclusions
Clinical trials of blood pressure lowering drugs show consistent reductions in the incidence of stroke [49]. However, there is still scope for better treatment of hypertension, particularly in the elderly with systolic hypertension where endothelial dysfunction is an unmet clinical need [41], [50]. In addition, exaggerated blood pressure responses during exercise with reduced heart rate recovery post exercise are associated with increased cardiovascular mortality, due to endothelial dysfunction
Funding
This study was supported by a grant (to R. Corder) from Barry Callebaut Belgium NV.
Acknowledgements
Mr. Clovell M. David for technical assistance and Mr. Michael G. Taylor for patient recruitment.
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