A new systematic review from researchers in Poland indicates that caffeine consumption can alter the quality of sleep by changing the brain's electrical patterns, even if the total time spent asleep remains unaffected. The research, published in the journal Nutrients, suggests that caffeine may make sleep less restorative than it subjectively feels.
The analysis synthesized the results of 32 human studies that used electroencephalography (EEG) to measure brain activity during sleep following caffeine intake. A primary finding was that caffeine can suppress slow-wave activity, a key marker for deep, restorative sleep, particularly during the first part of the night. The researchers also observed an increase in faster brainwave patterns, which is associated with a lighter, less restful state of sleep.
A significant conclusion from the review is the disconnect between perception and physiological reality. In multiple studies, participants reported feeling that they had slept well, while EEG recordings showed clear evidence of sleep disruption. This suggests individuals may not be aware of the reduction in sleep quality. The effect was also pronounced in recovery sleep, where caffeine appeared to hinder the brain's natural ability to compensate for prior sleep deprivation.