Cocoa Flavanols Improve Vascular Responses to Acute Mental Stress in Young Healthy Adults

Abstract

Mental stress has been shown to induce cardiovascular events, likely due to its negative impact on vascular function. Flavanols, plant-derived polyphenolic compounds, improve endothelial function and blood pressure (BP) in humans, however their effects during stress are not known. This study examined the effects of acute intake of cocoa flavanols on stress-induced changes on vascular function. In a randomised, controlled, double-blind, cross-over intervention study, 30 healthy men ingested a cocoa flavanol beverage (high-flavanol: 150 mg vs. low-flavanol < 4 mg (-)-epicatechin) 1.5 h before an 8-min mental stress task). Forearm blood flow (FBF), BP, and cardiovascular activity were assessed pre- and post-intervention, both at rest and during stress. Endothelial function (brachial flow-mediated dilatation, FMD) and brachial BP were measured before the intervention and 30 and 90 min post-stress. FMD was impaired 30 min post-stress, yet high-flavanol cocoa attenuated this decline and remained significantly higher compared to low-flavanol cocoa at 90 min post-stress. High-flavanol cocoa increased FBF at rest and during stress. Stress-induced cardiovascular and BP responses were similar in both conditions. Flavanols are effective at counteracting mental stress-induced endothelial dysfunction and improving peripheral blood flow during stress. These findings suggest the use of flavanol-rich dietary strategies to protect vascular health during stress.

Keywords: cocoa flavanols; endothelial function; forearm blood flow; mental stress.

Figure 1

Experimental Study Design.

Figure 2

Time course of Heart rate (A), Heart rate variability (B), Pre-ejection period (C) and Systolic and Diastolic blood pressure (SBP, DBP) (D) before (pre-intervention baseline) and following either a high-flavanol cocoa or low-flavanol cocoa, at rest and during stress (8-min PASAT). Data are presented as Mean ± SEM. Post-hoc analyses were conducted using Bonferroni’s multiple comparison test. *** HR, HRV, PEP, SBP and DBP were significantly different during stress, compared to rest and pre-intervention baseline, for both conditions (p < 0.001). ** SBP was significantly greater during rest compared to pre-intervention baseline (p < 0.01). * DBP was significantly greater during rest compared to pre-intervention baseline (p < 0.05). (N = 10–13 for HR, HRV and PEP; N = 30 for BP).HR, heart rate; HRV, heart rate variability; PEP, pre-ejection period; SBP, systolic blood pressure; DBP, diastolic blood pressure; BP, blood pressure, PASAT, paced-auditory-serial-addition-task, SEM, standard error of mean

Figure 3

Forearm blood flow (A) and Forearm vascular conductance (B) following high-flavanol cocoa or low-flavanol cocoa at rest and during stress (8-min PASAT). Values are % change from pre-intervention baseline, and presented as Mean ± SEM. Post-hoc analyses were conducted using Bonferroni’s multiple comparison test. FBF was significantly greater following high-flavanol cocoa compared to low-flavanol cocoa *** during rest (p < 0.001) and ** during stress (p < 0.01). ### FBF and FVC were significantly greater during stress compared to rest (p’s < 0.001). $$ FBF and FVC were significantly greater following high-flavanol cocoa compared to low-flavanol cocoa (p’s < 0.01) (N = 29). FBF, forearm blood flow; FVC, forearm vascular conductance; PASAT, paced-auditory-serial-addition-task; SEM, standard error of mean

Figure 4

Time course of flow-mediated dilatation of the brachial artery (FMD, %) before and after consumption of either a high-flavanol cocoa or low-flavanol cocoa, at 30 and 90 min post-stress (8-min PASAT). Data are presented as Mean ± SEM. Post-hoc analyses were conducted using Bonferroni’s multiple comparison test. *** FMD was significantly greater at 30 min post-stress (corresponding to 2 h following flavanol consumption) (p < 0.001), and * 90 min post-stress (corresponding to 3 h following flavanol consumption) (p < 0.05), following high-flavanol cocoa compared to low-flavanol cocoa. ### FMD was significantly lower at 30 min post-stress (corresponding to 2 h following flavanol-consumption), compared to pre-intervention baseline (p < 0.001) (N = 30).