Background: Mental stress has been shown to induce acute endothelial dysfunction. Black ethnicities experience a disproportionately higher burden of cardiovascular disease, with stress-related vascular responses proposed as a contributing factor. Although flavonoid-rich foods, particularly cocoa flavanols, can mitigate stress-induced decline in endothelial function, evidence in high-risk populations remains limited. This study investigates the influence of cocoa flavanols on vascular responses to mental stress in healthy, black male volunteers.
Methods: A randomised, placebo-controlled, double-blind, counterbalanced within-subject acute study was used to evaluate the effects of cocoa flavanols on stress-induced vascular responses. Healthy black participants (n=9) completed two sessions and consumed either a high-flavanol cocoa (150 mg (-)-epicatechin) or a low-flavanol cocoa (< 4 mg (-)-epicatechin), prior to undergoing mental stress (8-minute paced auditory serial addition task: PASAT). Vasodilatory responses (forearm blood flow, FBF), systolic and diastolic blood pressure (BP), heart rate (HR), heart rate variability (HRV), and pre-ejection period (PEP), were assessed pre-flavanol consumption (Baseline), post-flavanol consumption at rest (Rest) and during mental stress (Stress). Endothelial function (as measured by brachial artery flow-mediated dilatation, FMD) was assessed at Baseline and 30-and-90 minutes post-mental stress (i.e., 2-3-hours post-flavanol intake).
Results: Preliminary results (n = 9) show that stress induced significant increases in systolic and diastolic BP, HR, HRV, and PEP in comparison to baseline (Baseline/Rest, p’s<.05). FBF also significantly increased during stress compared to Baseline (p= .004, +2.19 ± 0.46). There was no significant decline in FMD following mental stress, yet FMD was significantly higher 30 minutes post-stress following high-flavanol cocoa compared to low-flavanol cocoa (p=.014, +2.74 ± 0.87) and compared to Baseline (p=.024, +2.10 ± 0.60). No differences in PASAT performance were observed between dietary interventions (p= .0678). Data from a full sample of 14 participants is expected to be analysed by April 2026.
Conclusion: The mental stress task evoked the expected cardiovascular and vasodilatory responses across both dietary interventions. Whilst cocoa flavanols did not affect physiological responses during stress, they did improve endothelial function following mental stress in young, black participants.
Keywords: mental stress, cardiovascular diseases, endothelial function, cocoa flavanols, ethnicity