Caffeine at night disrupts sleep patterns, preventing the brain from resetting

Caffeine is woven into daily life, turning up not just in morning coffee but in tea, chocolate, soda, and energy drinks.

Yet the same stimulant that keeps billions of people alert may also be changing the way the sleeping brain resets itself overnight, according to new research from the University of Montréal.

In a recent study, scientists combined electroencephalography with artificial-intelligence tools to reveal that evening caffeine drives the brain into a more active and less restorative mode during sleep. Researchers also found the effect is most pronounced in people under 30.

Probing the sleeping brain

The research team, led by doctoral trainee Philipp Thölke in the Cognitive and Computational Neuroscience Laboratory (CoCo Lab), recorded the nighttime brain activity of 40 healthy volunteers.

Each participant slept in the lab twice: one night after caffeine and another night after placebo, both taken before bed.

Throughout the night, electroencephalogram (EEG) electrodes tracked the electrical chatter of neurons, while sophisticated algorithms searched for subtle patterns.

“We used advanced statistical analysis and artificial intelligence to identify subtle changes in neuronal activity,” Thölke said.

His project involved a collaboration with Karim Jerbi, the director of CoCo Lab and a professor of psychology, and sleep-and-aging specialist Julie Carrier.

Caffeine heightens brain activity

When the researchers compared the caffeine nights with the placebo nights, they saw a clear jump in what neuroscientists call signal complexity. The EEG traces looked more intricate, less predictable, and closer to the patterns typical of wakefulness.

The team also measured an increase in “criticality,” a concept that Professor Jerbi likens to an orchestra finding its perfect pitch. “Criticality describes a state of the brain that is balanced between order and chaos,” he said.

“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. In this state, the brain functions optimally: it can process information efficiently, adapt quickly, learn and make decisions with agility.”

Caffeine, he noted, nudges the brain into that same poised, ready-to-learn condition useful at noon, perhaps unwelcome at midnight.

“Caffeine stimulates the brain and pushes it into a state of criticality, where it is more awake, alert, and reactive. While this is useful during the day for concentration, this state could interfere with rest at night: the brain would neither relax nor recover properly,” Carrier explained.

Caffeine’s impact on sleep

Beyond complexity metrics, the EEG recordings showed noteworthy shifts in traditional sleep rhythms.

Under the influence of caffeine, the slow theta and alpha waves crucial for repair and memory were suppressed in non-REM sleep. Meanwhile, faster beta activity, typical of mental engagement while awake, appeared more often.

“These changes suggest that even during sleep, the brain remains in a more activated, less restorative state under the influence of caffeine,” Jerbi said.

Age makes a difference

The volunteers ranged from 20 to 58 years old, allowing the team to see how age influences caffeine’s punch.

Young adults from 20 to 27 exhibited the strongest boost in criticality and the greatest suppression of slow waves, especially during REM sleep. That age skew likely stems from biology. Youngsters have more adenosine receptors in the brain, giving caffeine – an adenosine blocker – extra leverage.

“Adenosine receptors naturally decrease with age, reducing caffeine’s ability to block them and improve brain complexity, which may partly explain the reduced effect of caffeine observed in middle-aged participants,” Carrier said.

Caffeine use at night

Taken together, the findings suggest that an after-dinner espresso may not only delay sleep but also reduce its quality. For students and young professionals who lean on late-day lattes, the data raise particular concerns, since their brains appear most sensitive.

Yet the study’s authors are cautious about sweeping prescriptions. They note that caffeine’s popularity – consumed by an estimated 80 percent of adults worldwide – makes nuanced guidance essential.

Future work will need to unravel how the observed neural changes translate into next-day performance, long-term cognitive health, and individual differences tied to genetics or existing sleep disorders.

Still, the research shows that sleep is not simply unconscious downtime. The brain finely tunes its overnight choreography, and stimulants can shift its rhythm.

As the researchers continue to explore how common substances alter criticality and complexity, they hope to inform personalized recommendations. This could help coffee lovers balance the perks of daytime alertness with the necessity of deep, restorative sleep.

The study is published in the journal Nature Communications Biology.

—–

Like what you read? Subscribe to our newsletter for engaging articles, exclusive content, and the latest updates. 

Check us out on EarthSnap, a free app brought to you by Eric Ralls and Earth.com.

—–