Flavonoids are small molecules that can be found ubiquitously in plants (e.g. cocoa, berries, grapes, apples) and can protect humans against vascular disease, as evidenced by improvements in peripheral endothelial function, likely through nitric oxide (NO) signalling. Emerging evidence also suggests that diets rich in these compounds may protect against cognitive decline later in life, but the underlying mechanisms are not well established.

We have conducted randomized, counterbalanced, double-blind, placebo controlled, within-subject acute studies in healthy young adults to investigate the effects of one single dose of cocoa flavonoids (flavanols) on prefrontal cortical oxygenation using Near Infrared Spectroscopy (NIRS). In our first study (N=18), we showed that flavanol intake leads to faster (approx. 1 min; p < 0.001) and greater brain oxygenation (p=0.030 for Oxygenated Haemoglobin, O₂Hb ) in response to hypercapnia (5% CO₂), as well as higher performance in a Stroop Task, only when cognitive demand is high (p=0.045). We further observed that only participants who benefitted from flavanol intake during hypercapnia, also demonstrated improvements during cognitive performance (1). More recently we have also shown that cocoa flavanols might be beneficial in the context acute mental stress. During periods of stress, individuals often increase their consumption of unhealthy foods, especially high fat foods, and it is well established that both fat and mental stress alone can negatively impact peripheral vascular function. However, their effects on the cerebral vasculature are less understood. We have firstly demonstrated that a high-fat breakfast (56.5 g fat) impaired prefrontal cortical oxygenation (p<0.05 for O₂Hb and Tissue Oxygenated Index, TOI) during the mental stress episode in healthy young volunteers, in comparison to a low fat-breakfast (11.4 g fat) (N=19). In a follow-up study (N=23), we have further investigated whether a high-fat breakfast administered with an acute dose of cocoa flavanols may prevent fat-induced impairments in cortical oxygenation during stress. We are currently analysing this set of data and will be able to share at the meeting.

Together our data suggests that flavonoid-rich foods might be an effective dietary strategy to improve cortical oxygenation in young healthy adults and that might be important in the context of high cognitive demand and during periods of stress. These findings will have important implications for future research to explore the relationship between food choices and cerebral haemodynamics during cognitive performance/mental stress. Our data further suggests that flavonoids might exert similar actions on the cerebral vasculature as they do in the peripheral vasculature.