How Coffee Affects Sleep: A Large Study Challenges a Popular Myth

A recent large-scale study has called into question the widespread belief that regular coffee consumption significantly worsens sleep. The research, published in the journal PLOS ONE, found that among middle-aged people the habit of drinking coffee may have little to no impact on either sleep quality or levels of daytime fatigue.

Scientists analyzed data from a large Swedish population sample and compared the amount of coffee consumed with various sleep indicators — including subjective assessments of sleep quality and feelings of sleepiness during the day.

The results turned out to be unexpected: researchers found almost no statistically significant link between regular caffeine consumption and poorer sleep.

Even among people who drank coffee more frequently and in larger amounts, sleep indicators on average were nearly the same as among those who consumed it less often.

The researchers suggest that the explanation may lie in the brain’s adaptation to caffeine. With long-term and regular consumption, the body gradually adjusts to its effects, and the stimulating impact of the substance becomes less pronounced.

In particular, the adenosine system may play a role — a neurotransmitter system involved in regulating wakefulness and sleepiness. Over time, the sensitivity of this system may change, reducing caffeine’s influence on sleep.

However, the authors emphasize that their findings do not mean caffeine is completely harmless for sleep. Previous experimental studies have shown that large doses of caffeine — especially in the evening — can shorten total sleep duration, increase the time it takes to fall asleep, and reduce the proportion of deep sleep stages.

According to the researchers, the effect of coffee on sleep may be far more individual than previously thought. Factors such as age, genetic characteristics, caffeine consumption habits, and overall health can all influence how coffee affects sleep.

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