Coffee can steal your deep sleep

Researchers from the University of Wroclaw Medical School have found that the effect of caffeine is often not that people can’t fall asleep for longer or sleep less, but that their sleep quality becomes poorer. Even with a standard amount of sleep, the brain exhibits patterns similar to those of wakefulness, and the deep sleep phase is reduced. As a result, the body spends the required hours in bed, but fails to fully recover.

Slow waves in the deep sleep phase play a critical role: they are responsible for tissue regeneration, replenishment of energy resources and optimization of brain function. When their activity decreases, a person may subjectively feel like they have had enough sleep, although the neurophysiological recovery has not been complete. This explains why, after a seemingly full sleep, some people still feel tired and less focused.

The reaction to caffeine varies greatly from person to person. It is influenced by genetic characteristics, metabolic rate, age, stress levels, and accumulated fatigue. For some, a cup of coffee in the evening goes unnoticed, while others find that even a morning espresso can interfere with their ability to fully rest. The key factor is the total amount of caffeine consumed throughout the day and whether the body has had time to eliminate it before bedtime.

This information is particularly important for individuals who regularly rely on caffeine to enhance their productivity, such as office workers, athletes, and students. The result is a vicious cycle: daytime fatigue leads to the desire for another cup of coffee, but caffeine, in turn, impairs the quality of sleep, further contributing to fatigue. It turns out that caffeine can take energy from future sleep, which has to be paid for by a decrease in the effectiveness of rest.

Experts emphasize: caffeine is a biologically active substance, and its effects depend on a variety of factors: dose, time of reception, individual characteristics and lifestyle. It is not unambiguously harmful or beneficial; it is important to consider the context of its use. Modern research is increasingly focused not on the duration of sleep, but on its neurophysiological characteristics — it is they who give a more accurate picture of how well the body recovers at night.