In a study published in the journal Scientific Reports, researchers have demonstrated that consumption of cocoa flavanols can improve efficiency in blood oxygenation in the frontal cortex — a brain region that plays a key role in planning, regulating behavior and decision-making — of young healthy people and that it is likely to contribute to improvements in cognitive function, but only when cognitive demands are high.
Flavanols, a sub-group of plant flavonoids, are present in cocoa, grapes, apples, tea, berries and other foods.
They are known to have a beneficial effect on cardiovascular health, but their effects on brain health are not well understood.
“Flavanols are small molecules found in many fruits and vegetables, and cocoa, too,” said senior author Dr. Catarina Rendeiro, a scientist in the School of Sport, Exercise and Rehabilitation Sciences at the University of Birmingham.
“They give fruits and vegetables their bright colors, and they are known to benefit vascular function.”
“We wanted to know whether flavanols also benefit the brain vasculature, and whether that could have a positive impact on cognitive function.”
The researchers tested 18 participants before their intake of cocoa flavanols and in two separate trials, one in which the subjects received flavanol-rich cocoa and another during which they consumed processed cocoa with very low levels of flavanols.
About two hours after consuming the cocoa, participants breathed air with 5% carbon dioxide — about 100 times the normal concentration in air.
“This is a standard method for challenging brain vasculature to determine how well it responds,” said first author Professor Gabriele Gratton, a researcher in the Beckman Institute for Advanced Science and Technology and the Department of Psychology at the University of Illinois at Urbana-Champaign.
“The body typically reacts by increasing blood flow to the brain. This brings in more oxygen and also allows the brain to eliminate more carbon dioxide.”
With functional near-infrared spectroscopy, a technique that uses light to capture changes in blood flow to the brain, the authors measured oxygenation in the frontal cortex.
“This allows you to measure how well the brain defends itself from the excess carbon dioxide,” said co-author Professor Monica Fabiani, also from the Beckman Institute for Advanced Science and Technology and the Department of Psychology at the University of Illinois at Urbana-Champaign.
The team also challenged participants with complex tasks that required them to manage sometimes contradictory or competing demands.
Most of the participants had a stronger and faster brain oxygenation response after exposure to cocoa flavanols than they did at baseline or after consuming cocoa lacking flavanols.
“The levels of maximal oxygenation were more than three times higher in the high-flavanol cocoa versus the low-flavanol cocoa, and the oxygenation response was about one minute faster,” Dr. Rendeiro said.
After ingesting the cocoa flavanols, participants also performed better on the most challenging cognitive tests, correctly solving problems 11% faster than they did at baseline or when they consumed cocoa with reduced flavanols.
There was no measurable difference in performance on the easier tasks, however.
“This suggests that flavanols might only be beneficial during cognitive tasks that are more challenging,” Dr. Rendeiro said.
Within the study cohort, there was a small group who did not benefit at all from the flavanol-enriched drink in terms of blood oxygenation levels, and who also did not derive any cognitive benefit.
This group was shown to have existing high levels of brain oxygenation responses to start with that were not increased further by drinking the enriched cocoa.
“Although most people benefited from flavanol intake, there was a small group that did not,” Dr. Rendeiro said.
“Four of the 18 study subjects had no meaningful differences in brain oxygenation response after consuming flavanols, nor did their performance on the tests improve.”
“Because these four participants already had the highest oxygenation responses at baseline, this may indicate that those who are already quite fit have little room for improvement.”
“Overall, the findings suggest that the improvements in vascular activity after exposure to flavanols are connected to the improvement in cognitive function.”
G. Gratton et al. 2020. Dietary flavanols improve cerebral cortical oxygenation and cognition in healthy adults. Sci Rep 10, 19409; doi: 10.1038/s41598-020-76160-9