A single dose of cacao, which is rich in certain plant compounds, can improve reaction time and decision-making skills during physically and mentally exhausting exercise. These cognitive benefits occur even when individuals feel similarly mentally drained, suggesting that their brains are unconsciously improving their performance. The research results were published in a magazine psychopharmacology.
Hayato Tsukamoto, a researcher at Waseda University’s Faculty of Sport Science, led the investigation. His team wanted to understand how mental fatigue affects physical performance and whether nutritional supplements might have a protective effect. They focused on a mental process known as executive function.
Executive function is a cognitive system that helps people manage their thoughts, direct their attention, and control impulses. During sports such as soccer and basketball, athletes constantly utilize this system to make quick choices and block out distractions. Maintaining this mental sharpness is essential to high levels of athletic performance.
When people use their executive functions for long periods of time, they experience a state of cognitive fatigue. This mental exhaustion slows down your reaction time and makes you more prone to errors. Physical exercise, such as running or cycling, can increase this feeling of fatigue and further impair decision-making ability.
To combat this decline, researchers turned to flavanols, natural compounds found in cocoa tree seeds. These seeds are the main ingredient used to make chocolate. Past studies have shown that cocoa flavanols act as antioxidants in the human body.
Antioxidants are substances that help protect cells from damage by harmful molecules. Previous tests revealed that cocoa flavanols may reduce mental fatigue when people are just sitting at a desk. Tsukamoto and his colleagues wanted to see if these compounds could protect decision-making skills when people exercise and think hard at the same time.
The researchers recruited 18 healthy young men in their early 20s for the experiment. They utilized a placebo-controlled crossover design in their trial. This design means all participants complete the experiment twice on separate days, comparing the real supplement to a dummy pill.
One day, the men took capsules containing 500 milligrams of cocoa flavanols. On other days, they took capsules containing only 50 milligrams of the compound that acted as a placebo. The capsules looked exactly the same, so participants had no idea which one they had swallowed.
After ingesting the capsules, the men waited an hour for the plant compounds to reach maximum levels in their bloodstream. Next, they completed a short 5-minute mental test to establish baseline brain performance. This mental assessment is known as the color word Stroop task.
Color word tasks test your ability to process contradictory information and suppress erroneous impulses. For example, the word “red” may appear on the screen printed in blue ink. Participants must press a button that corresponds to the ink color, not the written word.
After baseline testing, the men began a grueling 50-minute exercise session. They simultaneously completed a continuous version of a color word task while riding a stationary bike at a moderate pace. This combined effort is designed to induce high levels of cognitive fatigue.
Throughout the sessions, the researchers tracked how quickly the men responded and how well they processed contradictory information. They also monitored heart rates and asked the men to rate their own mental fatigue. Finally, the team took blood samples to check for biological markers of cellular stress.
One hour after taking the capsules, and before they started exercising, the men showed clear improvements in cognitive function. High-dose cocoa capsules produced faster reaction times on the most confusing parts of mental tests compared to lower-dose capsules. Higher doses also improved the ability to filter distracting information during rest.
The cognitive effects of high doses of cocoa persisted even after a 50-minute cycling session. As the men pedaled, they responded more quickly to contradictory verbal prompts. The overall ability to stay focused and suppress erroneous impulses was better when taking high-flavanol capsules.
Even small improvements in reaction time can be meaningful in competitive sports. Researchers pointed out that subtle differences in decision-making speed can determine the outcome of major sporting events. A fraction of a second determines whether a player intercepts a pass or reacts to a referee’s call.
Despite improving performance, high doses of cocoa didn’t actually change how the men felt. Both trials reported exactly the same levels of mental fatigue and physical strain. Differences in subjective fatigue were not statistically significant.
Blood tests also showed no changes in oxidative stress markers or a specific protein called brain-derived neurotrophic factor. This protein normally promotes brain cell growth and health. Because these blood markers do not change, the exact biological processes that cause the improvement in reaction time remain unknown.
Researchers believe that flavanols may improve blood flow in the brain. Previous research suggests that cocoa compounds can enhance blood vessels’ response to increased oxygen demand. When a person exercises and thinks hard at the same time, the brain has to divide its resources between the motor cortex and the prefrontal cortex.
The motor cortex controls body movement, and the prefrontal cortex handles decision-making and concentration. Improving vascular function with flavanols may help provide enough oxygen to both brain regions at once. This enhanced delivery may explain faster reaction times even when participants felt completely exhausted.
The research team acknowledged that the experiment had some specific limitations. This study only included male participants, which limits how broadly the conclusions can be applied. Women experience natural hormonal fluctuations throughout the menstrual cycle, which can affect cognitive function and reaction time.
Future studies should investigate the effects of cocoa flavanols on decision-making quality in female participants. Scientists need to consider the potential effects of changing estrogen levels. This will help determine whether the cognitive benefits of cocoa apply equally to all athletes.
The researchers also noted that the blood tests only looked for a single marker of cell damage. Measuring other biological markers may reveal exactly how cocoa flavanols protect the brain during physical stress. Assessing brain-specific markers, rather than simply measuring circulating blood levels, may provide a more accurate answer.
Scientists also need to consider different dosing and timing strategies to find the best way to use cocoa supplements. The current study showed that a dose of 500 milligrams was effective. Finding the ideal intake frequency may provide a practical nutritional strategy for competitive athletes.
The study, “Single consumption of flavanol-rich cocoa improves inhibitory executive processes under cognitive fatigue during aerobic exercise in men: a randomized, double-blind, placebo-controlled crossover study,” was authored by Hayato Tsukamoto, Sota Yonetani, Takahiro Koyama, Asuka Suzuki, Ai-Wayan Yuki, Kento Dora, and Tsuyoshi Hashimoto.
