Your Oura ring or Apple Watch may holds secrets about your health that you didn’t even realize.
There’s a lot wearables can tell us, from estimates of the calories we’ve burned to our heart rate variability to how much sleep we got last night.
But hiding in that sleep data is a metric that may mean more than meets the eye.
Researchers of a new study published in PLOS Medicine found that it could be a predictor of disease risk, including everything from dementia to type 2 diabetes.
The team looked at sleep tracker data from over 95,000 people over the course of one week — then checked in on those people about nine years later.
They found that more REM sleep — the stage when we dream — was associated with a lowered risk of 83 different diseases and conditions affecting nearly every part of the body.
Those include blood and immune disorders, heart conditions, skin conditions, metabolic conditions such as obesity and type 2 diabetes, gastrointestinal conditions, bacterial and viral infections, mental health and substance use disorders musculoskeletal conditions such as arthritis, neurological conditions such as Alzheimer’s disease, and respiratory illnesses such as COPD.
The associations even extended to outcomes such as wheelchair dependence.
The strongest associations were a lower risk of cannabis dependence (74% lower risk), Parkinson’s (72%), multiple sclerosis (52%), wheelchair dependence (49%), dementia (46%), Alzheimer’s (31%), and heart failure (26%).
Deep sleep, the phase before REM, was also associated with lowered risk of seven conditions: anemia, type 2 diabetes, anxiety, major depressive disorder, arthritis, Parkinson’s, and sleep apnea.
The best way to know how much REM sleep you’re getting is by getting a polysomnography (PSG) at a sleep clinic, where techs attach special sensors to detect brain waves, rapid eye movement, and temporary paralysis in the limbs that happens during REM.
But sleep trackers do their best to estimate REM sleep by combining data on movement, heart rate and pulse changes.
Why might more REM sleep lead to healthier outcomes?
There are four different stages of sleep. Stage 1 is the lightest, when we transition to awake to asleep and our heartbeat, breathing, and eye movements slow down.
Stage 2 is a slightly deeper light sleep, when our bodies relax further. We spend most of the night here.
Stage 3 is deep sleep or slow-wave sleep, the hardest to wake up from.
Finally, there is REM sleep, which stands for “rapid eye movement” — your eyes move, heart rate and breathing increase, but your arms and legs stay still.
REM is essential for memory, moving new information from temporary storage to long-term knowledge. This is also necessary for problem solving. REM is also needed for mood regulation and brain development in children.
Every night, you should be going through that four-stage sleep cycle four to six times. Each time, the REM phase lengthens — first, it’s just a few minutes. By the end of the night, it might be around a half hour.
Overall sleep time is also important. For dozens of conditions — including type 2 diabetes, COPD, dementia, chronic kidney disease and depression — people who slept six to eight hours had the lowest risk. By comparison, people who slept less than five hours had a higher risk of 37 conditions.
Researchers also found that sleeping for different lengths of time from night to night was associated with a higher risk of abdominal pain, anxiety and major depressive disorder.
