Caffeine reduces sleep quality by altering brain activity

Researchers using electroencephalography (EEG) have found that caffeine can diminish the restorative quality of sleep even when it does not cause obvious awakenings or delay the onset of sleep.

While traditional sleep assessments often focus on sleep duration and the frequency of waking up, quantitative EEG analysis allows scientists to observe subtle changes in brain electrical activity. According to Professor Donata Kurpas of Wroclaw Medical University, caffeine can reduce slow-wave activity, which is a critical marker of deep sleep associated with physical recovery and maintaining healthy brain function.

Even if an individual sleeps for a full duration, caffeine may shift EEG patterns toward a more ‘wakeful’ state, meaning the brain does not achieve the same level of neurological recovery as it would without the stimulant.