The strongest link between sleep and disease may not be how many hours you log, but how much of that time is spent in REM and deep sleep.
A phenome-wide analysis of 95,559 UK Biobank participants, published September 17, 2026 in PLOS Medicine, tracked wrist accelerometer data for a week and followed the group for a median of 8.9 years.
More REM sleep was associated with lower risk of dozens of conditions.
More deep sleep, the slow-wave stage that dominates the first part of the night, was linked to lower risk of type 2 diabetes and major depressive disorder, among a smaller set of seven conditions.
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At the other end sat the short sleepers. People averaging less than five hours a night faced increased risk of 37 conditions, the most elevated vulnerability the researchers identified.
The authors conclude that maintaining six to eight hours of sleep is associated with a more favorable sleep architecture and lower disease risk.
Why the stages matter
Sleep is not a single flat state. During REM sleep, the brain is nearly as active as when you are awake, and the muscles go limp so you cannot act out your dreams, the National Heart, Lung, and Blood Institute explains.
Deep sleep, also called slow-wave sleep, is the stage the body appears to lean on hardest for physical repair.
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The new work is the first to link these stages, measured across a large real-world population, to more than a thousand disease outcomes.
The team, led by Shengzhi Sun at Capital Medical University in Beijing, used a deep-learning model to estimate sleep stages from the wrist data.
Read the caveats carefully
That method is also the study's biggest weakness.
Independent experts have flagged that a watch does not measure sleep stages directly.
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Reverse causation is another concern. When the researchers pushed the exclusion window out to two years, only 95 of the original 156 associations held up.
That pattern suggests early, undiagnosed disease may itself have been reshaping people's sleep before diagnosis.
What is known to eat into these stages
Habits already tied to shorter deep and REM sleep are the practical starting point.
Alcohol in the evening can cut into deep sleep even at modest amounts, and a warm bedroom pushes the body out of the deeper stages earlier in the night.
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Six to eight hours in bed remains the duration linked to the healthiest sleep architecture, and less than five is where the risk signal spikes.
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This article is made and published by Ida-Marie Palm Varbæk, who may have used AI in the preparation.