How Your Evening Coffee Could Be Affecting Your Brain During Sleep? Study Finds Out

A new study published in Communications Biology by researchers from Universite de Montreal reveals that caffeine disrupts the brain's ability to recover during sleep by increasing neural complexity and reducing restorative brain rhythms-effects that are especially pronounced in young adults. The findings suggest that caffeine, though beneficial for alertness during the day, may impair nighttime recovery and memory consolidation, prompting researchers to call for more personalized guidelines on caffeine intake based on age and health.

Caffeine is found not only in coffee but also in tea, chocolate, soft drinks, and energy drinks, making it the most widely consumed psychoactive substance globally. While its daytime stimulating effects are well documented, its nighttime impact on the sleeping brain has remained largely underexplored.

To address this, the research studied 40 healthy adults using electroencephalography (EEG) and artificial intelligence. Each participant underwent sleep monitoring on two occasions: once after taking caffeine capsules three and one hour before bed, and once after taking a placebo.

The analysis revealed that “caffeine increased the complexity of brain signals, reflecting more dynamic and less predictable neuronal activity, especially during the non-rapid eye movement (NREM) phase of sleep that’s crucial for memory consolidation and cognitive recovery,” said Philipp Thölke, a research trainee at UdeM's Cognitive and Computational Neuroscience Laboratory. Caffeine also disrupted slow brain waves such as theta and alpha-essential for deep sleep-while increasing beta wave activity, typically linked with wakefulness.

Lab's director Karim Jerbi, a psychology professor and researcher at Mila -- Quebec AI Institute said, “These changes suggest that even during sleep, the brain remains in a more activated, less restorative state under the influence of caffeine.”

Young adults aged 20 to 27 were more affected than older participants. The researchers urge further study to guide age-specific caffeine recommendations and understand its broader effects on cognitive health.

Reference: Philipp Thölke, Maxine Arcand-Lavigne, Tarek Lajnef, Sonia Frenette, Julie Carrier, Karim Jerbi. Caffeine induces age-dependent increases in brain complexity and criticality during sleep. Communications Biology, 2025; 8 (1) DOI: 10.1038/s42003-025-08090-z