Brain Oxygenation And Cognition In Healthy Adults Boosted With Cocoa Flavanols

This may be the first study to find a positive effect of eating foods rich in flavanols on brain vascular function and cognitive performance in young healthy adults according to Catarina Rendeiro, a researcher and lecturer in nutritional sciences at the University of Birmingham who led the research with the University of Illinois at Urbana-Champaign psychology professors Monica Fabiani and Gabriele Gratton.

"Flavanols are small molecules found in many fruits and vegetables, and cocoa, too," Rendeiro said. "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.”

This study involved 18 healthy young adult non-smokers without known heart, brain, vascular or respiratory disease with the assumption that any effects in this population would provide robust evidence that dietary flavanols can improve brain function in healthy people. 

Participants were tested before consuming cocoa flavanols in 2 separate trials: during one they received flavanol-rich cocoa and in the other processed cocoa with very low levels of flavanols. Both studies were double-blind with neither the researchers nor participants knowing which type of coca was being consumed in the trials to prevent the researchers’ and participants’ expectations from affecting the results. 

Participants breathed in air with 5% carbon dioxide which is about 100 times the normal concentration of air about 2 hours after consuming the cocoa, this is a standard method for challenging brain vasculature to determine how it responds. Typically the body reacts by increasing blood flow to the brain to bring more oxygen and allow the brain to eliminate more carbon dioxide. 

Using near-infrared spectroscopy the researchers measured oxygenation in the frontal cortex, which is a brain region that plays an important role in planning, regulating behavior and decision making. This measurement allowed the researchers to tell how well the brain was defending itself from the excess carbon dioxide. 

The participants were also challenged with complex tasks that required managing sometimes contradictory or competing demands. After exposure to cocoa flavanols most of the participants had stronger and faster brain oxygenation responses than at baseline or after consuming cocoa lacking in flavanols, according to the researchers. 

"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," Rendeiro said.

Participants also performed better on the most challenging cognitive tests, correctly solving problems 11% faster after ingesting cocoa flavanols than at baseline or after ingesting the cocoa with reduced flavanols. However, there was no measurable difference in performance on the easier tasks. Additionally, participants varied in their responses to exposure to cocoa flavanols. 

"This suggests that flavanols might only be beneficial during cognitive tasks that are more challenging," Rendeiro said. “Although most people benefited from flavanol intake, there was a small group that did not," Rendeiro added. 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," Rendeiro said. "Overall, the findings suggest that the improvements in vascular activity after exposure to flavanols are connected to the improvement in cognitive function."

“Future work should focus on systematically employing difficulty-graded cognitive challenges when assessing the efficacy of dietary flavonoids on human cognitive function,” the researchers wrote. “Most importantly, our data can potentially open new avenues for precision-medicine research with regard to understanding individual responses to flavanol intake and helping to identify populations that might benefit the most from interventions.”