Coffee doesn’t have to keep you awake to disrupt your sleep

Caffeine can reduce the restorative capacity of sleep. This effect can occur even if a person falls asleep normally and stays in bed for eight hours. EEG (electroencephalogram) recordings revealed that caffeine leads to fewer slow brain waves. These waves are associated with deep sleep. Individual sensitivity to caffeine varies significantly among people. This means that even caffeine consumed earlier in the day can affect nighttime recovery for some individuals.