by Megan Finnegan
Flavanols are a group of compounds found in cocoa, the central ingredient of chocolate, are well known to improve vascular function in the arms, hands, legs, and feet. In a recent article co-authored by Psychology professors Drs. Fabiani and Gratton, researchers showed that these circulatory benefits can be seen in the brain and in cognitive performance. They found that within two hours of ingesting a flavanol enriched cocoa drink, participants not only showed more responsive blood vasculature, but that this change translated to increased cognitive performance on difficult tasks.
In order for the brain to effectively respond to cognitive demands, it must regulate blood flow to neurons, increasing blood flow when neurons increase their activity. Previous research on the effects of flavanols reported mixed results in changes to blood flow with some showing increased blood flow and some showing decreases. These studies also showed inconsistent results as to whether flavanols consumption led to better cognitive performance. Professors Fabiani and Gratton along with Catarina Rendeiro and a team of collaborators from the University of Birmingham hypothesized that some of this discrepancy could be due to flavanols only exerting their benefits when the cognitive task was difficult and neuronal demand was particularly high.
To test this, researchers recruited 18 volunteers who each received either a low flavanol cocoa drink or a similar drink with high flavanol content. Their brain's ability to respond to increased need for oxygen was tested by having the volunteers inhale air enriched with carbon dioxide, which signals to the body that more oxygenated blood should be delivered to tissue. After 2 hours, participants were then asked to engage in a modified version of a task of selective attention known as the Stroop task while their brains were scanned for changes in blood flow. In this task, volunteers must either read the color word (i.e. the words 'red', 'blue', or 'green') or, in the harder task, respond to the color of the font the word is written in, which necessitates suppressing a tendency to read the word. For example, if they see the word ‘red’ written in a green font then, in the harder task, they must say green and not red.
The researchers found that high-flavanol intake not only increased the brain's ability to provide more oxygen-rich blood when demand was high, but that this translated to increased performance on the modified Stroop task. Interestingly, this improvement in cognitive function was only seen in the most demanding version of the task, which required the highest levels of attention and response control to perform. While most of the volunteers did see cognitive improvements after ingesting the flavanol rich drink, a few did not. When the researchers compared the brain's blood flow response between these two groups, they found that those that did not see cognitive improvements also did not have improvements in response to blood flow demands. This suggests that the key mechanism of flavanol performance benefits may lie in its ability to improve blood flow to the brain.
While this all may seem like reason for chocolate lovers to rejoice, even dark chocolate can be full of fat, sugar, and excess calories with some manufacturing processes removing much of the flavanol content. The research team points out in their work that there exist other known methods of increasing performance on cognitively demanding tasks, including regular exercise. It has been hypothesized that exercise may also function by a similar mechanism of improving blood supply to the brain. So although you may see some benefit from that holiday chocolate, moderation is probably still the best policy.
This research was reported in:
Gratton, G., Weaver, S.R., Burley, C.V. et al. Dietary flavanols improve cerebral cortical oxygenation and cognition in healthy adults. Sci Rep 10, 19409 (2020). https://doi.org/10.1038/s41598-020-76160-9