A study led by University of Warwick Professor Jianfeng Feng has found that regularly sleeping too little is associated with depression and brain loss in emotion areas, while sleeping too long is associated with cognitive decline and degenerative diseases.

Sleeping the right amount is crucial for long-term health. Seven hours has recently been proposed as the average amount of sleep to aim for as an adult, yet some people regularly get too little, while others get more than they need.

"How many hours of sleep do you get in every 24 hours?"This question was asked to almost half a million adults aged 38–73 from the UK Biobank database. The researchers in this study then classified them into those who slept fewer than seven hours, aka "short sleepers," and those who slept more than seven hours, aka "long sleepers." Their sleeping habits were then examined alongside data on their health outcomes, their genetic information and brain imaging data.

Professor Feng, School of Computer Science, The University of Warwick asked, "Is short sleep and long sleep part of the same biological process, or are they distinct pathways with different effects on health? Answering these questions is crucial for developing targeted strategies to improve sleep health among aging populations."

Their analysis, published in Nature Mental Health, found that regularly sleeping short durations is linked to psychological problems, such as low mood and fatigue, and poorer muscle and skeletal health (reduced vitamin D and IGF-1).

Brain scans showed that short sleepers have reduced brain matter in brain areas involved in emotion, a biological consequence of cutting sleep short. Sleeping short durations was also found to be a risk factor for a variety of conditions such as depression, heart disease and obesity.

Sleeping long hours, on the other hand, was associated with cognitive decline, higher inflammation and poorer metabolic health (lower "good" cholesterol). Brain scans showed brain matter loss in areas associated with memory and known risk areas for degenerative disease. Long sleep was associated with diseases such as Alzheimer's and schizophrenia. However, sleeping long durations appears to be a symptom, rather than a cause, of these conditions.

Ultimately, genetic analysis showed long sleep and short sleep to be biologically distinct, with their own genetic associations, as opposed to viewing short sleep and long sleep as two extremes of the same process, which is more intuitive.

On the significance of this work, Professor Feng added, "This study represents a paradigm shift in how we understand the relationship between sleep and health. Short sleep is often an underlying cause of health issues, whereas long sleep tends to reflect pre-existing conditions. These findings highlight the importance of personalized interventions to address the unique biological pathways of short and long sleepers.

"Our ultimate goal is to construct a comprehensive sleep health profile across the human lifespan, providing actionable insights for individuals at every stage of life."

This work will be important for establishing meaningful sleep management strategies for aging populations. Future work will expand this research out to more life stages and diverse populations.

More information: Yuzhu Li et al, Divergent biological pathways linking short and long sleep durations to mental and physical health, Nature Mental Health (2025). DOI: 10.1038/s44220-025-00395-6