A study conducted in the United States found that people with a lower proportion of "REM sleep" (a state of light sleep in which the eyes move quickly when sleeping) are at higher risk of death.
Examining the effects of REM and non-REM sleep on health
Human sleep consists of two qualitatively different sleep states, non-REM sleep and REM sleep, which alternate during nighttime sleep. REM sleep is "light sleep" in which the brain is relatively active although it is asleep, and the eyeballs move quickly when sleeping, so the English word "Rapid Eye Movement" is used. It was named REM sleep for short. REM sleep is a state in which the muscles of the whole body are relaxed and the body is resting. On the other hand, non-REM sleep is a state of "deep sleep" in which brain activity is also reduced.
Sleep disorders have been reported to be associated with increased risk of cardiovascular disease (myocardial infarction and stroke), metabolic disease (such as diabetes), mental illness, cognitive decline, and even increased risk of death. .. However, many of the sleep studies conducted so far have used the sleep time and condition declared by the subject for analysis. Therefore, the effects of REM sleep and non-REM sleep on health and death have not been investigated.
Therefore, researchers at Stanford University and others have decided to objectively investigate the ratio of REM sleep to sleep time and analyze the relationship with death.
The authors first enrolled 5994 men aged 65 and over living in the city at six facilities in the United States and analyzed data from long-term follow-up observational studies. After registration, participants wore polysomnography and wrist physical activity monitors during sleep at home to record body and brain activity during sleep. REM sleep accounted for 0-43.9% of participants' sleep time, and this variability was considered to be within the normal range. The average was 19.2% (69.7 minutes).
A 13% increase in mortality risk for every 5% decrease in REM sleep rate
Of the 2675 people (all male, average age 76.3 years) who had the information needed for the analysis, 1404 (52.5%) died during a follow-up period of approximately 12 years (median).
An analysis that considers various factors that can affect the relationship between REM sleep and death shows that for every 5% reduction in REM sleep, the risk of death from any cause (total mortality) is 13 It turned out to increase by%. Similarly, a 5% reduction in the rate of REM sleep suggested an 11% increase in the risk of death from cardiovascular disease and a 19% increase in the risk of death from other causes.
In addition, when the risk of death increases significantly when the rate of REM sleep falls below a certain level, we examined whether there is a threshold, and found that people with a rate of REM sleep less than 15% had total deaths compared to those with a rate of 15% or more. It was shown that the risk of death by cause of death may be increased.
Similar results confirmed in younger populations, including women
The authors then sought to see if data from another study, including women, would give similar results. We included data from observational studies in Wisconsin, USA, that enrolled men and women between the ages of 30 and 60 and followed them from 1988 to the present. Participants spent the night at a medical institution after registration and were tested with a polysomnography meter.
After about 21 years (median) follow-up of 1386 qualified individuals (mean age 51.5 years, 54.3% male), 184 (13.3%) died.
Compared to the first study, this study had a longer follow-up period and a younger average age in the subjects, but the proportion of REM sleep was similar, ranging from 0-43.0%. The average was 17.6% (67.8 minutes). In this population as well, lower rates of REM sleep were associated with a higher risk of total mortality, with a 5% decrease in the rate of REM sleep increasing the overall risk of death by 17%. This increased risk was significant only in women.
Finally, we examined the relationship between survival and the ratio of REM sleep to non-REM sleep in N1 stage (light sleep), N2 stage (moderate sleep), and N3 stage (deep sleep) in sleep time. The strongest relationship was shown to be the rate of REM sleep.
The study, which included two populations with different gender ratios and mean ages, showed a strong relationship between REM sleep rates and mortality risk. "In the future, we need to find out how REM sleep affects mortality risk," the researchers said.
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