Caffeine Disrupts Brain’s Recovery During Sleep, Especially in Young Adults

A new study shows why caffeine hits young brains harder during sleep.

Photo Smoothies/Shutterstock

Even when you manage to fall asleep after drinking caffeine, your brain doesn’t truly rest. It stays locked in an active and alert state throughout the night, according to new research.

“Caffeine is the most widely consumed psychoactive stimulant worldwide. Yet important gaps persist in understanding its effects on the brain, especially during sleep,” the study authors wrote.

When Your Brain Can’t Rest

The study, recently published in Communications Biology, found that caffeine increases what scientists call “criticality” in the brain—essentially keeping neural activity too active and chaotic during sleep when it should be winding down for recovery.

“Criticality describes a state of the brain that is balanced between order and chaos,” co-lead study author Karim Jerbi, a psychology professor and researcher at Mila-Quebec AI Institute, said in a statement. “It’s like an orchestra: too quiet and nothing happens, too chaotic and there’s cacophony. Criticality is the happy medium where brain activity is both organized and flexible.”

While this heightened brain state is beneficial during waking hours for concentration and focus, it becomes problematic at night. “The brain would neither relax nor recover properly,” said study co-author Julie Carrier, a professor of sleep and psychology.

The Science Behind Disrupted Sleep

Researchers studied 40 healthy adults using artificial intelligence and brain wave monitoring (EEG) technology. Participants underwent sleep studies on two separate nights: once taking caffeine capsules three hours and one hour before bed, and once with a placebo at the same times.

The team found that caffeine made brain signals more dynamic and less predictable, especially during non-rapid eye movement (non-REM) sleep, the phase crucial for memory consolidation and thinking recovery.

The study authors also observed that caffeine reduced delta wave activity, which is closely linked to deep, restorative sleep, while simultaneously increasing beta wave activity, which is associated with wakefulness.

Caffeine also makes brain activity more complex and less predictable throughout the night, according to lead study author and research trainee Philipp Tholke.

“These changes suggest that even during sleep, the brain remains in a more activated, less restorative state under the influence of caffeine,” Jerbi said. “This change in the brain’s rhythmic activity may help explain why caffeine affects the efficiency with which the brain recovers during the night, with potential consequences for memory processing.”

Younger Adults Hit Hardest

The findings showed the effects were more pronounced in adults aged 20 to 27 compared to middle-aged participants aged 41 to 58, especially during REM sleep, a phase associated with dreaming.

As people age, their adenosine receptors decline, making caffeine less effective at blocking them and boosting brain activity, Carrier said, which may partly explain why caffeine seems to work less in middle-aged people.

Given caffeine’s widespread daily use, especially as a remedy for fatigue, the researchers emphasized the importance of understanding its complex effects on brain activity across different age groups. They suggest that further research is needed to determine how these neural changes impact cognitive health and daily functioning, and to develop personalized caffeine consumption recommendations.

What It Means for Memory and Learning

While caffeine can help give us a mental boost, timing is important.

When taken later in the day, it shifts the brain into a more active and alert state, Leah Kaylor, a licensed clinical and prescribing psychologist specializing in sleep, told The Epoch Times.

“[This] might seem helpful at first, but this increased brain activity during sleep can interfere with the very processes that make sleep so important—like memory consolidation and learning,” she said.

Kaylor pointed out that our brains use the different stages of sleep to process and store information. Deep sleep is critical for solidifying new facts and ideas, while REM sleep helps us process emotions and connect ideas in creative ways.

However, by blocking adenosine, caffeine can reduce the amount of deep sleep we get and interfere with REM sleep.

“This means that even if you manage to fall asleep after drinking caffeine, the quality of your sleep—and the brain’s ability to learn and remember, can be significantly reduced,” Kaylor said.

The research points to a simple but crucial solution: Timing matters. And more than most people realize.

“You want caffeine to work for you, not against you, and that means timing it right,” Dr. Joseph Mercola, board-certified family physician and author of “Your Guide to Cellular Health,” told The Epoch Times. While our sensitivity to caffeine tends to decrease with age, he noted, younger brains are more vulnerable to overstimulation.

If you’re under 40 and you drink caffeine late in the day, it can keep your brain in a state of heightened criticality, “too active, too chaotic,” for hours after you fall asleep, Mercola said. “So, regardless of age, I suggest you cut off caffeine by early afternoon,” he said.

Mercola added that those who track their sleep with wearable devices and notice fragmented or shallow rest should consider a “caffeine reset.”

“Pull it for a few days and see how your body responds,” he said. “Quality sleep is one of your brain’s non-negotiable needs.”