Dietary flavanols improve cerebral cortical oxygenation and cognition in healthy adults

Abstract

Cocoa flavanols protect humans against vascular disease, as evidenced by improvements in peripheral endothelial function, likely through nitric oxide signalling. Emerging evidence also suggests that flavanol-rich diets protect against cognitive aging, but mechanisms remain elusive. In a randomized double-blind within-subject acute study in healthy young adults, we link these two lines of research by showing, for the first time, that flavanol intake leads to faster and greater brain oxygenation responses to hypercapnia, as well as higher performance only when cognitive demand is high. Individual difference analyses further show that participants who benefit from flavanols intake during hypercapnia are also those who do so in the cognitive challenge. These data support the hypothesis that similar vascular mechanisms underlie both the peripheral and cerebral effects of flavanols. They further show the importance of studies combining physiological and graded cognitive challenges in young adults to investigate the actions of dietary flavanols on brain function.

Figure 1

Haemodynamic responses in frontal cortical regions during hypercapnia (5% CO₂) both before (0 h) and after (2 h) intake of either a low- or high-flavanol dietary intervention. Time course for Oxygenated (a) and Deoxygenated-haemoglobin (b) are presented as relative changes from baseline (room air) and averaged across participants (N = 17) and across frontal brain locations. The average relative concentrations of oxy- (c) and deoxy haemoglobin (d) during minutes 3–4 of the CO₂ challenge (corresponding to maximal dilation) show that the high-flavanol intervention induces significantly higher oxygenation levels than the low-flavanol at 2 h post-intervention (*p = 0.030). No significant differences are observed for deoxygenated haemoglobin (Mean ± SEM).

Figure 2

Brain maps of oxygenated haemoglobin during hypercapnia (5% CO₂) both before (0 h) and after (2 h) intake of either a low- or high-flavanol dietary intervention. (a) Oxy-haemoglobin concentration changes (in z scores) across frontal cortical regions and averaged across participants (N = 17) are presented at the time of onset (0 h) and 1, 2, 3, and 4 min into the CO₂ challenge. Brain maps, viewed from the top, are oriented as indicated in the inset diagram: F = front, B = back, L = left, R = right; Darker grey background color indicates the recording area. (b) Latency to reach 90% maximal blood oxygenation was significantly lower (***p < 0.001) by approximately 1 min after the high-flavanol intervention in comparison to low-flavanol (Mean ± SEM).

Figure 3

Cognitive performance in a modified version of the Stroop task 2 h after intake of either a low- or high-flavanol dietary intervention. Inverse efficiency score (IES) is described as reaction time/accuracy (expressed in seconds) during cognitive performance across four different conditions representing progressively harder cognitive demands (a). The Double-Stroop condition induces the slowest cognitive processing (higher IES) compared to the other conditions (word, colour and Stroop). The benefit of the high-flavanol intervention (lower IES) in only apparent in the Double Stroop condition, when the level of conflict is higher. The cognitive benefit of high-flavanol cocoa in the Double Stroop over and above the other cognitive tasks is significantly higher in comparison to the low-flavanol intervention (*p = 0.045) (b). Two sub-groups of volunteers, (i): N = 13 and (ii): N = 4, revealed distinct oxy-haemoglobin benefits from flavanols during hypercapnia (c); with only the sub-group (i) showing benefits from flavanols during both the hypercapnia challenge and the cognitive task (d). The data is presented as Mean ± SEM.