- A new study found that 300 mg of caffeine had no effect on participants’ cognitive performance.
- While past studies have found caffeine to be helpful, other issues like participants’ chronobiology, habitual caffeine intake, and other confounding factors may have been at play.
- Experts explain why chronobiology may sway the results.
Every day, millions of Americans have a cup of coffee—or tea, or matcha, or other caffeinated beverage—to jump-start their day. And many believe it makes a big difference, whether they need physical energy to perform manual labor or the sustained focus necessary for a desk job.
But while experts agree caffeine has a clear effect in some scenarios, a growing body of research suggests it’s more complicated than it appears at first blush: There is a consensus that caffeine can boost more basic cognitive functions, such as reaction time, but it’s less clear whether it helps with more complex ones.
A new study published in Nutrients set out to investigate caffeine’s effect on higher-order cognitive functions—and found that, when administered in the morning an hour before testing, caffeine did not improve cognitive performance or reactive agility. “Caffeine also did not meaningfully affect mood, tiredness, alertness, withdrawal symptoms, or core and skin temperatures,” says João Agulhari, B.Sc., study coauthor and postgraduate researcher in sport and exercise science at Liverpool John Moores University.
So does this mean your coffee habit isn’t actually helping you power through your inbox? Ahead, experts break it down.
Meet the experts: João Agulhari, B.Sc., study coauthor and postgraduate researcher in sport and exercise science at Liverpool John Moores University; Kenneth Lee, M.D., medical director of the Sleep Disorders Center at UChicago Medicine.
What did the study find?
The researchers recruited 51 recreationally active men between the ages of 18 and 30. All participants regularly consumed less than 150 mg of caffeine on average—a key distinction, as some of caffeine’s effects may in part be attributable to the alleviation of withdrawal symptoms. They also tended to go to bed between 10 p.m. and 11:30 p.m. and wake up between 6 a.m. and 7:30 a.m., and agreed to standardize their sleep schedule on the night before testing.
This allowed the researchers to ensure the results weren’t swayed by participants’ individual circadian rhythms. “Previous studies have also differed considerably in their control of sleep, time of day, habitual caffeine intake, familiarization and placebo effects,” Agulhari explains. “We wanted to examine caffeine under tightly standardized early-morning conditions.”
They divided participants into three groups: Those given 300 mg of caffeine an hour before testing, those given a placebo an hour before testing, and those who weren’t given anything before testing. The tests the researchers administered were designed to assess participants’ learning, memory, processing speed, visuomotor skills, selective attention, decision-making skills, and reactive agility.
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After crunching the data, the researchers concluded that there was no significant difference between those who were given caffeine and those who were given a placebo or no pill at all. “Importantly, this does not mean caffeine can never affect cognitive or agility performance,” Agulhari says. “It means that in well-rested, recreationally active young men with relatively low habitual caffeine consumption, this dose provided no measurable benefit during our standardized early-morning protocol.”
In the paper, the researchers suggest that controlling for participants’ chronobiology, along with other aspects like regular caffeine consumption, may partly explain why this study didn’t find an effect, while similar studies in the past did. “In certain circumstances, caffeine may primarily reverse sleep loss, withdrawal, or an unusually low level of alertness rather than enhance performance above a well-rested and standardized baseline,” Agulhari says.
In addition, this study set out to evaluate higher-order cognitive tasks, rather than lower-order ones, which may be more affected by caffeine. “[Caffeine] may therefore be most effective when performance is limited by sleepiness or reduced alertness. However, making someone feel more awake does not necessarily improve the complex integration of information required for executive function or decision-making,” Agulhari says. “These tasks may also depend on an optimal level of arousal, rather than simply more arousal.”
Why might accounting for chronobiology affect the study’s results?
In addition to affecting the endocrinologic, gastrointestinal, cardiac, and other bodily systems, “chronobiology and our circadian rhythm play a crucial part in terms of cognition and executive functioning,” says Kenneth Lee, M.D., medical director of the Sleep Disorders Center at UChicago Medicine. By recruiting participants whose circadian rhythms are roughly average—meaning they’re not extreme night owls or extreme early birds, but somewhere in the middle—the researchers were able to remove a potentially confounding variable. “Those that could have been on either extreme of the spectrum could have had increased variability in their response to the caffeine,” Dr. Lee says.
This is because caffeine works by blocking receptors in your brain for a chemical called adenosine, and extreme night owls and early birds may have different levels of that chemical, which “builds up the longer you are awake and is driven off during your sleep,” Dr. Lee explains.
What’s the takeaway?
Don’t pour out that cup of joe just yet. Agulhari stresses that this study is just one piece of a set of four studies conducted by the same team, each investigating how caffeine affects physical or cognitive performance—one of which found an improvement in strength among those who had caffeine.
“Considering the series as a whole is important because caffeine’s effects appear to be specific to the type of performance being assessed,” he says. “Finding no benefit for cognition or reactive agility does not mean that caffeine cannot benefit other aspects of physical performance.”
It’s also important to keep in mind that the study’s participants were drawn from a very specific group and tested under very specific conditions. “Responses could differ in women, elite athletes, people with higher habitual caffeine intake, different chronotypes, or individuals tested after breakfast,” Agulhari says.
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