Most sleep advice comes down to one number: hours in bed. A large new analysis suggests the makeup of those hours may matter as much as the total. In data from more than 95,000 adults who wore a wrist tracker for a week, people who spent more of the night in REM sleep had a lower risk of 83 separate diseases over the following decade. More deep sleep was linked to lower risk of a smaller set of conditions, including type 2 diabetes and depression.
How the study worked
The research comes from a team led by Shengzhi Sun at Capital Medical University in Beijing and was published in PLOS Medicine on September 17, 2026. It draws on the UK Biobank, a long-running British health study. Participants averaged about 56 years old when they wore a wrist accelerometer, a movement sensor similar to the one in a fitness watch, around the clock for seven days.
A wrist sensor can't see brain waves, so the researchers used a machine-learning model called SleepNet to estimate time spent in light, deep, and REM sleep. The model had been trained on more than 1,100 nights in which people wore an accelerometer while also being monitored with lab polysomnography, the gold-standard sleep test. The team then followed participants for a median of 8.9 years. They used hospital records to see who developed any of more than 1,000 diseases, and they checked each one against each sleep measure.
What they found
REM sleep showed the broadest pattern. Comparing people at the lower and upper ends of the typical range, about 48 extra minutes of REM, was linked to lower risk of 83 conditions. The reported numbers for a few of them are striking:
- Heart failure: about 26% lower risk (hazard ratio 0.74)
- Dementia: about 46% lower risk (hazard ratio 0.54)
- Parkinson's disease: about 80% lower risk (hazard ratio 0.20)
Deep sleep was linked to fewer conditions. More slow-wave sleep was associated with lower risk of seven conditions, including type 2 diabetes and major depressive disorder. Light sleep was mixed: it was tied to seven conditions, with lower risk for some and higher risk for others, including depression.
Total sleep still mattered. For 69 conditions, the lowest risk fell within roughly 6 to 8 hours a night. People sleeping under 5 hours carried the widest spread of risk, with higher odds of 37 conditions.
Why REM might matter so much
REM is the stage when most vivid dreaming happens. It usually comes in longer stretches toward morning, which is one reason cutting your night short tends to cost REM first. The brain is highly active during REM, and earlier research has tied REM to memory consolidation, emotional processing, and heart-rate and blood-pressure regulation. Several of the conditions in this study are neurological, such as dementia and Parkinson's. That fits a long-standing observation: changes in REM sleep, including acting out dreams, can appear years before Parkinson's is diagnosed.
That last point is also the biggest reason for caution. If early, undiagnosed disease is already disrupting someone's REM, then low REM could be an early sign of illness rather than its cause. The researchers ran extra analyses to address this reverse-causation problem but acknowledge it can't be ruled out. A roughly 80% lower Parkinson's risk is exactly the sort of number this effect could inflate.
Not sure how well you're really sleeping?
Our free Sleep Score & Fixes tool looks at your habits and schedule and suggests specific, practical changes. It's a quick way to spot what may be eating into your deeper and later-night sleep.
The limits worth knowing
- It's observational. The study shows associations, not proof that more REM prevents disease. The authors say so directly.
- Wrist trackers estimate sleep stages. The authors describe SleepNet's accuracy as moderate, and it underestimated REM by about 17 minutes compared with lab testing. Your own watch's "REM" number deserves the same skepticism.
- One week is a snapshot. Sleep was measured for seven days, once, with years of follow-up afterward.
- The group isn't everyone. UK Biobank volunteers skew healthier and wealthier than average, and diseases were counted only when they appeared in hospital inpatient records.
What you can actually do with this
You can't directly command your brain into more REM, and chasing a tracker's stage numbers often backfires by making people anxious about sleep. The more useful lesson is about what tends to protect REM and deep sleep:
- Protect the back half of the night. REM concentrates in the final hours, so an alarm that cuts sleep short trims REM most. A consistent wake time with enough time in bed is the simplest fix. Our Sleep Schedule Builder can help you plan one.
- Go easy on evening alcohol. Alcohol is well known to suppress REM, especially early in the night.
- Get snoring and gasping checked. Untreated sleep apnea fragments REM in particular. See our overview of sleep apnea symptoms.
- Don't trade the 6–8 hour window for anything. Very short sleep showed the broadest risk in this study. The American Academy of Sleep Medicine still recommends at least 7 hours for adults.
For more on what each stage does, see our guides to why REM sleep matters and the signs you're short on deep sleep.
Key takeaways
- A PLOS Medicine study of 95,559 UK Biobank adults linked about 48 more minutes of REM sleep to lower risk of 83 diseases over roughly nine years.
- The REM links included heart failure, dementia, and Parkinson's disease. More deep sleep was linked to lower risk of seven conditions, including type 2 diabetes and depression.
- For most conditions, the lowest risk fell within 6–8 hours of total sleep, and under 5 hours was tied to higher risk of 37 conditions.
- The findings are associations from wrist-tracker estimates, and early disease may itself reduce REM, so cause and effect aren't established.
- Practical takeaway: protect your full night, especially the REM-rich early-morning hours, rather than chasing tracker numbers.
The big picture lines up with what sleep researchers have argued for years: sleep is a set of distinct stages doing different jobs, not a single block of rest. This study can't tell you that more REM will prevent any particular disease. It does add weight to a simple habit: give your body the full night it needs to cycle through all of them.
Source: ScienceDaily (news release from PLOS) — "More REM sleep linked to lower risk of 83 diseases," September 23, 2026, https://www.sciencedaily.com/releases/2026/09/260923035930.htm. Study: Sun S. et al., "Accelerometer-derived real-world sleep stages and risk of incident diseases: A UK Biobank cohort study and phenome-wide association analysis," PLOS Medicine, September 17, 2026, doi:10.1371/journal.pmed.1005213.
Medical disclaimer: This article is for informational purposes only and does not constitute medical advice. The research described is observational and does not show that changing your sleep stages will prevent any disease. Talk to a qualified healthcare provider about sleep problems or any health concern before starting or changing treatment.
About Better Night Sleep: Better Night Sleep is an independent sleep-education and product-research resource. Our articles are written and edited by the Better Night Sleep editorial team using reputable public sources and established sleep-health recommendations. Learn more about us.