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“Is more sleep always better?”
Sleeping more than 8 hours may actually accelerate aging of the brain and heart.

Sleeping over 8 hours linked to a 40% higher risk of death
Sleep duration has a direct impact on depression

While insufficient sleep is widely known to be harmful, what about oversleeping? A large-scale study suggests that sleeping more than 8 hours a day—known as hypersomnia—may be just as concerning as sleep deprivation, serving as a signal of accelerated organ aging and increased disease risk. The findings are based on an AI analysis of health data from approximately 500,000 adults, examining aging rates across organs such as the brain, heart, lungs, liver, and immune system.

A research team from the AI and Biomedical Research Institute at Columbia University analyzed sleep duration and biological data from around 500,000 participants in the UK Biobank. Their findings were published on the 13th (local time) in the international journal Nature. The researchers combined self-reported sleep duration with blood tests, medical imaging, proteomics, and metabolomics data to create “aging clocks” that estimate biological age for individual organs. This large-scale study explored how sleep duration relates not just to fatigue or brain health, but to systemic aging indicators throughout the body.

The key finding was clear: both short sleep (less than 6 hours) and long sleep (more than 8 hours) were associated with higher organ aging markers, forming a U-shaped relationship. The lowest aging indicators were generally observed in those sleeping between 6.4 and 7.8 hours, although optimal duration varied slightly by organ and gender. Based on this, researchers categorized sleep into short (<6 hours), normal (6–8 hours), and long (>8 hours) for further analysis of disease and mortality risk.

Unlike previous studies that focused on overall biological age or specific areas like brain aging or cardiovascular disease, this research utilized plasma proteins, metabolites, and MRI data to construct 23 biological aging clocks, analyzing them at the organ level. The team explained that they aimed to determine whether the nonlinear relationship between sleep and aging extends beyond the brain to the entire body and molecular level.

The analysis found that 9 out of the 23 aging clocks showed a significant U-shaped relationship with sleep duration. Protein-based aging clocks revealed the strongest association in the brain, with similar patterns observed in the lungs, liver, immune system, and skin. Metabolite-based analyses showed links with the endocrine system, while MRI-based analysis connected sleep duration to aging markers in the brain, adipose tissue, and pancreas. These results suggest that both insufficient and excessive sleep can impact not only the brain but also metabolic, immune, and respiratory systems.

Disease risk was also elevated. Compared to individuals who slept 6–8 hours, both short and long sleepers showed associations with more than 150 diseases, both genetically and clinically. Short sleep was linked to depressive episodes, anxiety disorders, obesity, type 2 diabetes, hypertension, ischemic heart disease, and arrhythmias. Respiratory and digestive conditions such as chronic obstructive pulmonary disease (COPD), asthma, gastritis, and gastroesophageal reflux disease (GERD) were associated with both short and long sleep durations.

Mortality risk was likewise higher. Longitudinal data showed that individuals sleeping less than 6 hours had a 50% higher risk of death from all causes compared to those sleeping 6–8 hours. Those sleeping more than 8 hours had a 40% higher risk. This suggests that not only insufficient sleep but also excessive sleep may signal underlying health issues.

The researchers also analyzed late-life depression separately. Short sleep showed a relatively direct association with depression in older adults. In contrast, long sleep appeared to influence depression indirectly through accelerated aging in the brain and adipose tissue. This suggests that hypersomnia may not simply be a lifestyle habit, but rather a compensatory response reflecting underlying conditions such as neurodegeneration, metabolic dysfunction, or immune fatigue.

Overall, the study highlights that sleep should not be viewed merely as a lifestyle habit, but as a vital biological signal reflecting overall health. The researchers concluded, “Sleep disturbances may provide critical insights into healthy aging, disease risk, and longevity.”

Source: 한국경제 (https://www.hankyung.com/article/202605145359i)