Today, more people experience fatigue despite sleeping long enough. This is not only due to the duration of sleep, but also to its quality.
Research shows that the body gets less deep sleep, which is essential for recovery. As a result, eight hours in bed may not be sufficient.
According to National Geographic, researchers from Pennsylvania State University believe the issue is that the body does not receive the right signals to fully relax.
Disruptive screens
Digital habits play a major role. A 2025 study from Frontiers in Psychiatry shows that heavy smartphone use is associated with poorer sleep and increased mental restlessness.
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At the same time, constant stimulation from screens can make it difficult for the brain to settle.
Light from screens in the evening can keep the body awake by affecting hormones and making it harder to enter deep sleep.
Irregular routines
Sleep is also about timing. Researcher Kristen Knutson from Northwestern University explains to National Geographic that sleep at “wrong” times is less effective.
Irregular routines, such as sleeping in on weekends and waking up early on weekdays, can disrupt the body’s internal clock.
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The core problem is therefore not only a lack of sleep. It is that the body does not reach a state where it can truly recover.
Sources: National Geographic and Frontiers in Psychiatry.
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