Not every stage of sleep appears to offer the same benefits for the brain and body. New research found that greater amounts of rapid eye movement sleep, commonly known as REM sleep, were associated with lower risks of 83 diseases.

The conditions included dementia, Parkinson’s disease and heart failure. Greater amounts of deep sleep were separately associated with lower risks of seven conditions, including Type 2 diabetes and major depressive disorder.

The study involved 95,559 adults who wore wrist accelerometers continuously for seven consecutive days and nights. Researchers in China used deep learning algorithms to examine REM sleep, deep sleep, light sleep, total sleep duration, wakefulness after sleep onset and sleep irregularity.

Researchers then reviewed participants’ health records to examine associations with more than 1,000 diseases. The follow up period lasted nearly nine years, allowing the team to compare sleep patterns with later disease outcomes.

Greater REM sleep was associated with an 80% lower relative risk of Parkinson’s disease. It was also tied to a 46% lower risk of dementia and a 26% lower risk of heart failure.

Sleep duration also showed a strong association with disease outcomes. Sleeping between six and eight hours per night was associated with the lowest risk for 69 diseases, while fewer than five hours was linked to increased risk for 37 health conditions.

Consistency appeared important as well. Greater variation in sleep from one night to the next, along with more wakefulness during the night, was associated with higher risks of several conditions, including anxiety and substance use disorders.

The findings were published Sept. 17 in the journal PLOS Medicine. Although the results revealed wide ranging associations, experts cautioned that REM sleep alone should not be viewed as a guaranteed way to reduce disease risk.

“I think what is important is the total duration of sleep, and the percentage that REM takes up,” Oki Ishikawa, M.D., a pulmonary, critical care and sleep medicine expert at Northwell’s Northern Westchester Hospital, told Fox News Digital.

“The average percentage of REM sleep in this study population was about 20%, and generally 20-25% is considered normal per sleep cycle.” Ishikawa was not involved in the research and said he does not believe that simply increasing REM sleep will necessarily lower risk.

He pointed instead to the importance of getting enough sleep overall. Normal sleep patterns and sufficient duration are associated with functions such as maintaining good immune function and memory, according to Ishikawa.

Disrupted sleep may also serve as an early warning sign of disease rather than functioning only as a potential contributor. Dr. Chelsie Rohrscheib, head sleep expert at the New York sleep analysis company Wesper, said some diseases can begin disrupting sleep well before diagnosis.

“Conditions such as Parkinson’s disease, dementia and heart failure can begin affecting sleep years before they are diagnosed,” Rohrscheib, who was not involved in the research, told Fox News Digital. “At the same time, poor sleep may contribute to disease progression, so the relationship likely works both ways.”

The researchers acknowledged that the observational study could identify associations but could not prove that increasing REM or deep sleep directly prevents disease. Sleep was also measured for only one week with a wrist device rather than through a clinical sleep study.

“Some health information was collected years earlier, medications that can affect sleep were not fully considered and some medical diagnoses may have been missed,” Rohrscheib said. She also noted that UK Biobank participants were less diverse and generally healthier than the overall population.

That limitation means the findings may not apply equally to everyone. Rohrscheib also cautioned that wrist sleep trackers can estimate sleep stages but are not 100% accurate, making a formal laboratory sleep study necessary to know precisely how long someone spends in REM and other stages.

More research is needed to determine whether increasing REM or deep sleep can prevent specific diseases. Future studies could also examine whether the associations vary according to age, sex, overall health and other individual characteristics.

Ishikawa said treating sleep conditions such as sleep apnea could help optimize REM sleep. For people without a formal measurement, he suggested considering whether they feel refreshed after waking and whether they experience sleepiness during the day.

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