More REM Sleep Linked to Lower Risk of 83 Diseases, Including Dementia and Heart Failure

Importantly, the study shows an association, not proof that increasing REM sleep directly prevents disease. The research also found that a total sleep duration of around six to eight hours was associated with lower risk across many conditions.

Why REM Sleep Is Getting So Much Attention

Sleep is often reduced to a single question: How many hours did you get? But sleep isn't one uniform state. During a normal night, the brain moves through different stages, including light sleep, deep sleep and rapid eye movement, or REM, sleep. REM sleep is the stage most strongly associated with vivid dreaming. Brain activity becomes relatively active during this phase, and REM sleep is involved in processes related to memory, learning and emotional regulation. The new study adds another reason to pay attention to sleep architecture: the amount of REM sleep people get appeared to be associated with their long-term risk of several diseases. The scale of the research is what makes the finding particularly notable. Rather than examining one condition or relying entirely on people's recollection of their sleep, researchers looked at objectively collected sleep data and compared it with a very broad range of health outcomes.

What the Large Sleep Study Actually Found

Researchers from Peking University and Capital Medical University analysed data from 95,559 UK Biobank participants. The participants wore wrist-based accelerometers for about a week, allowing researchers to estimate different components of their sleep, including REM, light and deep sleep. The researchers then examined health records covering 1,049 different disease outcomes. Participants were followed until they developed a disease, died or reached the study's end date, with the median follow-up lasting 8.9 years. The results showed that greater REM sleep was associated with a lower risk of 83 diseases across 12 broad disease categories. The association wasn't limited to one part of the body or one type of illness. For every 47.6-minute increase in REM sleep — the study's interquartile range — the estimated risk of heart failure was 26% lower. The corresponding associations were a 46% lower risk of dementia, a 31% lower risk of Alzheimer’s disease and an 80% lower risk of Parkinsonism. Multiple sclerosis was also among the conditions showing a significant association. Those numbers may sound dramatic, but they need to be read carefully. They are relative risk estimates from an observational study, not evidence that adding 47.6 minutes of REM sleep will cause those diseases to become 26%, 46% or 80% less likely.

The Dementia Connection Is Particularly Interesting

The relationship between sleep and brain health has been studied for years, but this research provides a much broader look at how different sleep stages relate to future disease. In this study, greater REM sleep was associated with a lower risk of dementia and Alzheimer’s disease. The association remained statistically significant even after researchers performed several sensitivity analyses, including analyses designed to reduce the possibility that existing health problems were influencing the sleep findings. There is a biological reason researchers are interested in this area. Sleep is closely connected with memory processing, brain activity and the regulation of several physiological systems. However, the new study does not establish exactly why people with more REM sleep had lower disease risks. It is also possible that early, undiagnosed health problems affect sleep patterns rather than poor REM sleep causing those health problems. This is one of the reasons observational research needs to be interpreted cautiously.

Heart Health Also Stood Out

The cardiovascular findings are another important part of the research. More REM sleep was associated with lower risks of heart failure, atrial fibrillation and ischemic heart disease. The estimated hazard ratios were 0.74 for heart failure, 0.83 for atrial fibrillation and 0.87 for ischemic heart disease for the study's interquartile increase in REM sleep. That does not mean REM sleep should be considered a treatment for cardiovascular disease. Instead, the findings add to a growing body of research suggesting that sleep quality and sleep architecture are connected with cardiovascular health. Sleep and heart health can also influence each other. Conditions such as sleep disorders may disrupt normal sleep, while cardiovascular problems can affect how well a person sleeps. That two-way relationship makes it particularly difficult to determine cause and effect from observational data alone.

More Sleep Isn't Automatically Better

One of the most useful parts of the study is that it did not simply suggest that more sleep equals better health. Researchers found nonlinear relationships between total sleep duration and 86 disease outcomes. For 69 of these conditions, the minimum-risk duration was predominantly concentrated in the six-to-eight-hour range. Short sleep stood out as a particular concern. Compared with people sleeping six to eight hours, those sleeping less than six hours had higher risks for several conditions. After stricter statistical correction, significant associations remained for 24 disease outcomes, including heart failure, type 2 diabetes and chronic obstructive pulmonary disease. The strongest pattern appeared among people sleeping fewer than five hours. Of 41 significant associations identified across the different sleep-duration groups, 37 occurred in this very-short-sleep category. This reinforces an important point: sleep health isn't simply about chasing the largest possible number of hours.

REM Sleep Wasn't the Only Stage That Mattered

The researchers also examined deep sleep, and its associations were different. Greater amounts of deep sleep were associated with lower risks of seven diseases, including type 2 diabetes, major depressive disorder, sleep apnea and Parkinson's disease. The researchers also looked at light sleep, sleep irregularity and wakefulness after sleep onset. Sleep irregularity was associated with higher risks of several conditions, including anxiety and major depressive disorder. Spending more time awake after initially falling asleep was also associated with increased risks for a number of outcomes. In other words, the findings point toward sleep architecture as a whole, rather than suggesting that REM sleep is the only sleep stage that matters.

What the Study Does — and Doesn't — Prove

This distinction is essential. The study was observational. Researchers observed naturally occurring differences in sleep patterns and then looked at what happened to participants' health over time. They did not randomly assign people to receive different amounts of REM sleep. That means the research cannot establish that increasing REM sleep directly prevents dementia, heart failure or any of the other 83 diseases. Other factors could also contribute. Age, lifestyle, existing medical conditions, medications, socioeconomic factors and other characteristics may influence both sleep and disease risk. Although the researchers adjusted for demographic, lifestyle and environmental factors, they acknowledged that residual confounding remains possible. There is another limitation worth remembering: sleep stages were estimated using wrist-worn accelerometer data rather than measured with laboratory polysomnography, the clinical gold standard for detailed sleep-stage assessment. The researchers used a deep-learning algorithm to derive sleep stages from the wearable data, making the approach practical for a very large population but different from a full sleep-lab assessment.

What This Means for Everyday Sleep

The takeaway isn't that people should obsess over their smartwatch's REM percentage. A healthier interpretation is much simpler: consistent, sufficient sleep appears to be an important part of long-term health, and sleep quality may matter alongside sleep duration. For most adults, that means creating conditions that allow the brain to move naturally through its sleep cycles. Maintaining a reasonably consistent bedtime and wake time, limiting excessive evening caffeine, creating a dark and comfortable bedroom, managing late-night screen use and addressing persistent sleep problems can all support healthier sleep habits. If someone regularly snores heavily, wakes repeatedly during the night, experiences excessive daytime sleepiness or struggles to sleep despite having enough opportunity to do so, the answer isn't necessarily another sleep-tracking device. A discussion with a healthcare professional or sleep specialist may be more useful.

The Bigger Picture: Sleep Is More Than a Number

The most interesting message from this study may not actually be the number 83. It is the reminder that sleep is a complex biological process. Two people can both spend seven hours in bed and have very different sleep experiences. One may have relatively stable sleep with healthy cycling through different stages, while another may wake repeatedly or have an underlying sleep disorder. The researchers' findings suggest that looking beyond total sleep duration could provide a more detailed understanding of how sleep relates to future health. At the same time, the results don't justify treating REM sleep as a standalone medical target. For now, the evidence supports a more grounded approach: prioritise adequate, regular and good-quality sleep rather than trying to maximise one particular sleep stage. And if the occasional bad night has you worrying that you've somehow ruined your health, there's no need for that either. Sleep health is built over patterns and habits, not one restless Tuesday night.

FAQs

1. Does more REM sleep prevent dementia?

Not based on this study alone. Greater REM sleep was associated with a lower risk of dementia and Alzheimer’s disease, but the observational design means researchers cannot conclude that more REM sleep directly prevents these conditions.

2. How much REM sleep should an adult get?

The study did not establish a specific ideal number of REM minutes for individuals. Its findings support paying attention to overall sleep health rather than trying to force a particular amount of REM sleep.

3. Is six to eight hours of sleep enough?

The study found that the lowest-risk sleep duration for many disease outcomes was concentrated around six to eight hours. Individual sleep needs vary, so this should not be treated as a universal prescription.

4. Does deep sleep matter too?

Yes. Greater deep sleep was associated with lower risks of seven diseases in the study, including type 2 diabetes and major depressive disorder.

5. Can a smartwatch accurately measure REM sleep?

Consumer wearables can estimate sleep stages, but they are not equivalent to clinical polysomnography. The new study itself used accelerometer-derived estimates rather than full laboratory sleep studies.