The clock may say you slept seven hours, but your body knows better. What is new is how much the quality of those hours seems to matter.
People who got more REM sleep had an 80 percent lower risk of Parkinson's disease than those who got less.
Dementia risk was lower, according to a large new study published in September 2026 in PLOS Medicine.
Greater REM sleep was also linked to a lower risk of 83 different diseases in total.
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The study tracked 95,559 adults in the UK Biobank for a median of 8.9 years. Each participant wore a wrist sensor around the clock for seven days, and a machine-learning model estimated how much time they spent in each sleep stage.
Health records then showed who went on to develop which conditions.
What is REM sleep?
REM stands for rapid eye movement, the stage of sleep when the brain is almost as active as when you are awake and when most vivid dreams happen.
According to the Sleep Foundation, most adults need about two hours of REM sleep a night, which is roughly a fifth to a quarter of total sleep time.
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The researchers compared people across the normal range of REM sleep.
For every extra 47.6 minutes of REM sleep per night, the risk of Parkinson's disease dropped by about 80 percent, dementia by 46 percent, and heart failure by 26 percent.
These are relative reductions in risk, not promises for any one person. The study is observational, which means it can show a strong link but cannot prove that more REM sleep by itself prevents disease.
People who sleep well tend to differ from poor sleepers in many other ways too.
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Why the finding still matters
The size of the group and the use of wrist sensors instead of self-reports make this one of the most detailed looks yet at sleep stages and long-term health.
Deep sleep, a separate stage, was tied to a lower risk of 7 conditions, including type 2 diabetes and major depressive disorder.
Total sleep duration mattered too. Six to eight hours a night was linked to the lowest risk across 69 conditions, while sleeping less than five hours was tied to higher risk of 37 conditions. That mirrors earlier findings that both short and long sleep can be a problem.
How to give yourself more REM
There is no pill or shortcut that reliably boosts REM sleep. The honest answer is that REM comes with enough good-quality total sleep, especially in the second half of the night.
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Dr. Oki Ishikawa of Northwell's Northern Westchester Hospital told Fox News that about seven to nine hours of uninterrupted sleep gives you "the opportunity to cycle through REM in a sufficient way."
He added that treating an underlying sleep problem such as sleep apnea is often one of the most effective ways to get more REM.
The Sleep Foundation points to a few practical habits that protect REM. Keep a steady sleep and wake time, including on weekends. Cut back on alcohol in the evening, since it suppresses REM later in the night.
Limit bright screens close to bedtime, and keep the bedroom dark, cool and quiet.
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If you often feel tired after a full night in bed, snore heavily, or your partner notices long pauses in your breathing, that is worth bringing up with your doctor.
Treating a hidden sleep disorder is one of the few things that can meaningfully change how much REM sleep you actually get.
This article is made and published by Ida-Marie Palm Varbæk, who may have used AI in the preparation.