Your fitness tracker’s “REM” number might be worth a second look. A new study of more than 95,000 adults found that people who got more REM sleep had a lower risk of 83 different diseases over roughly nine years, including heart failure, dementia and Parkinson’s disease.
Before you start trying to “hack” your sleep stages, though, there’s a big asterisk. This research shows a link, not proof that more REM sleep protects you. Here’s what the scientists actually found, why outside experts are urging caution, and the simple, evidence-based sleep habits that are worth your time either way.
What Is REM Sleep, Anyway?
REM sleep (short for rapid eye movement sleep) is the stage of sleep when your eyes dart around behind closed lids, your brain becomes highly active, and most vivid dreaming happens. Your arm and leg muscles go temporarily limp during REM, which is why you usually don’t act out your dreams.
Across a typical night, your brain cycles through several stages again and again:
- Light sleep – the transition zone, where you spend a big chunk of the night.
- Deep sleep (also called slow-wave sleep) – the hardest stage to wake from, when brain waves slow way down.
- REM sleep – the active, dream-heavy stage that tends to get longer in the later part of the night.
Scientists have long suspected each stage does different jobs for the brain and body. What has been harder to pin down is how everyday, real-world sleep stages relate to long-term disease risk in big groups of people. That’s the gap this new study tried to fill.
Inside the REM Sleep Study
The research was published September 17, 2026, in the open-access journal PLOS Medicine by Shengzhi Sun of Capital Medical University in China and colleagues, according to a release from the journal’s publisher, PLOS.
Here’s how it worked:
- 95,559 people from the UK Biobank, a massive British health database, wore wrist accelerometers (movement-tracking devices, similar in concept to a fitness band) for seven straight days and nights.
- The team used a deep-learning algorithm to estimate how much time each person spent in REM, deep and light sleep, plus total sleep time, time awake after first falling asleep, and how irregular their sleep was from night to night.
- Participants were followed for a median of 8.9 years.
- Researchers checked health records for links to more than 1,000 disease outcomes.
The paper describes participants as middle-aged and older adults, with a mean age of about 56 at the start of the UK Biobank study.
What the Researchers Found
The headline results are eye-catching. Per the PLOS release:
- More REM sleep was associated with a lower risk of 83 diseases. For each extra 47.6 minutes of REM (the study’s comparison unit), the reported hazard ratios were 0.74 for heart failure, 0.54 for dementia and 0.20 for Parkinson’s disease. A hazard ratio below 1 means lower risk in that comparison.
- More deep sleep was linked to a lower risk of 7 conditions, including type 2 diabetes and major depressive disorder.
- Irregular sleep and more time awake after falling asleep were each tied to higher risk of several conditions, including anxiety and substance use disorders.
- Total sleep time had a curved relationship with risk. For many conditions, the lowest risk showed up in a 6-to-8-hour window. People sleeping less than 5 hours had higher risk of 37 conditions.
In total, the authors reported 156 significant links between sleep patterns and new diseases after a strict statistical correction for testing so many outcomes at once.
The authors called 6 to 8 hours of sleep “a health safeguard for middle-aged and older adults,” and suggested this may be because that range comes with a healthier mix of sleep stages.
The Big Caveats: Why REM Sleep Isn’t a Magic Shield
This is where it’s important to slow down. Even the study’s own press materials note that, as an observational study, it cannot show that sleep patterns directly cause disease risk. Independent experts who reviewed the paper for the UK’s Science Media Centre flagged several more issues.
1. Association is not causation
People who get more REM sleep may differ in lots of other ways – stress levels, income, activity, existing health. The authors themselves list residual confounding as a limitation, meaning other hidden factors could explain part of the link.
2. The sleep stages were estimated, not directly measured
The gold standard for measuring sleep stages is polysomnography, an overnight lab test that tracks brain waves, eye movements and more. This study inferred stages from wrist movement using an AI model. Dr. Greg Elder of Northumbria University noted that wristwatches “don’t explicitly measure eye movements, or brain activity.” Dr. Nina Rzechorzek of the University of Cambridge pointed out that the paper reports only moderate performance for the model’s stage classification.
3. Reverse causation is a real possibility
Diseases like Parkinson’s and dementia can quietly develop for years before diagnosis, and they may disturb sleep along the way. So in some cases, early disease may be changing sleep, rather than the other way around. When the researchers excluded diagnoses made in the first two years, only 95 of the original 156 associations held up, which Rzechorzek said suggests early or undiagnosed disease may already have been affecting sleep.
4. One week is a snapshot
Seven days of data is a lot for a study this big, but it can’t fully capture how someone slept over many years.
5. The UK Biobank isn’t everyone
The paper acknowledges a “healthy volunteer” selection bias. About 97% of the analyzed participants identified as White, and UK Biobank participants tend to be healthier and better-off than the general population. Results may not apply equally to younger adults or more diverse groups.
Rzechorzek summed it up: the results suggest sleep patterns could be useful markers of future disease risk, but they do not show that boosting REM or deep sleep, or forcing yourself into a 6-8 hour window, will prevent disease.
What This Means for Your Sleep (and Your Sleep Tracker)
So should you obsess over your watch’s REM score? Probably not. Consumer wearables estimate sleep stages in a similar way, and those estimates can be off. A “bad” REM night on your app isn’t a diagnosis.
The more useful takeaway is the one experts agree on: getting enough regular, good-quality sleep matters. Elder said the study adds to evidence that a regular sleep pattern with enough sleep is important for physical and psychological health as we age.
One note on hours: this study’s lowest-risk window was 6 to 8 hours, but the CDC recommends that adults ages 18 to 60 get 7 or more hours, based on guidance from the American Academy of Sleep Medicine and the Sleep Research Society. Don’t read this study as permission to cut back to 6.
If you’re curious how other nighttime habits may affect your body, check out our story on how sleeping with the light on may reshape your heart.
Evidence-Based Tips for Better Sleep
You can’t directly dial up your REM sleep, but you can give your body the best shot at healthy, uninterrupted sleep. The CDC recommends these habits:
- Keep a consistent schedule. Go to bed and wake up at the same time every day, including weekends.
- Set up your bedroom for sleep. Keep it quiet, relaxing and at a cool temperature.
- Power down early. Turn off electronic devices at least 30 minutes before bed.
- Watch late meals and alcohol. Avoid large meals and alcohol before bedtime.
- Cut off caffeine. Skip it in the afternoon and evening.
- Move your body. Exercise regularly and eat a healthy diet.
None of these are flashy, and that’s the point. As we reported when 63 experts ranked every longevity trend, the boring basics tend to beat the biohacks.
Talk to your doctor if you have persistent sleep problems. The CDC lists trouble falling asleep, waking up repeatedly during the night, and feeling tired even after enough sleep as signs of poor sleep quality. Conditions like insomnia and sleep apnea are common and treatable, and a provider can order a proper sleep study if needed.
REM Sleep Study FAQ
Does more REM sleep prevent dementia or heart disease?
No, this study can’t show that. It found that people with more estimated REM sleep had lower rates of many diseases, but it was observational, so other factors or early disease itself may explain the link.
How much sleep did the study link to the lowest risk?
For many conditions, the lowest risk fell in a 6-to-8-hour window, and fewer than 5 hours was tied to higher risk of 37 conditions. U.S. health guidance still recommends at least 7 hours for most adults.
Can I trust my smartwatch’s REM sleep data?
Treat it as a rough estimate. Wrist devices infer sleep stages from movement and other signals, while a lab sleep study measures brain activity and eye movements directly.
Who was in the study?
95,559 UK Biobank participants, mostly middle-aged and older, and about 97% White. Findings may not apply equally to everyone.
The bottom line: This is one of the largest looks yet at real-world sleep stages and long-term health, and it adds to a growing pile of evidence that sleep quality matters. But it doesn’t prove that chasing more REM sleep will protect you from disease. Focus on steady, sufficient sleep and healthy routines, and loop in your doctor if sleep is a constant struggle. You can read the full study in PLOS Medicine.
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