Married people experience longer durations of a deep sleep stage known as rapid eye movement (REM) sleep that helps form memories and regulate emotions, offering new clues about the potential health implications of marital status.
The findings, published in Frontiers in Psychiatry on May 10, showed that people who were married, and thus more likely to "co-sleep" with a partner, experienced REM sleep for significantly longer durations than people who had never been married. The paper is one of very few studies to analyze how people's "social sleep environment" may affect their quality of REM sleep using multiple direct physiological and biological measurements.
The authors offered several potential explanations of the results. For one, a partner's body heat may help to regulate the temperature of a sleeping environment, allowing for a more consistent sleep experience for their partner. Alternatively, one's spouse may provide a sense of security throughout the night, which may also help with sleep regulation, according to Henning Johannes Drews, a researcher at the Norwegian University of Science and Technology and the lead author of the study.
"Is it because your partner gives you the feeling of safety, or is it because [co-sleeping] just keeps the bed warm?" Drews asked during an interview with The Academic Times. "The most plausible significance of our findings is just that this might explain some of the beneficial effects of being in a relationship."
The researchers themselves have some degree of personal investment in the findings: Drews noted that he collaborated on the paper with his wife, research scientist Annika Drews, with whom he shares a bed each night.
REM sleep also appears to be greatly impacted by our circadian rhythms. Drews thinks that cohabitation, in some cases, may create a more consistent living environment that preserves one's own internal "timekeeper," resulting in more REM sleep. "If you live with a partner, that, of course, influences your behavior — your day-night rhythm," he said.
Another one of Drews' recent studies also focused on people in relationships, comparing their sleep quality when they slept alone with their sleep quality when sleeping with their partner. But because that study involved disrupting a couple's typical sleeping arrangement by asking them to sleep alone, it was difficult for researchers to determine whether and to what extent the study's structure influenced couples' sleeping patterns.
The role of REM sleep, a deep stage of sleep associated with the random darting of eyes, is still something of a mystery to researchers, but it may play a part in transforming recollections of recent life events into long-term memories. The REM state, which makes up about 20% of an average night of sleep, is also associated with vivid dreams, even paralyzing our bodies so that we do not act them out. For some individuals, this can cause an issue called sleep paralysis, in which the mind wakes up from a state of REM sleep while the body remains stationary.
Meanwhile, those with REM behavior disorder encounter the opposite problem: Their muscles can still move during REM sleep, which can result in them physically acting out their dreams. An undiagnosed case of REM sleep behavior disorder famously led standup comedian Mike Birbiglia to unwittingly jump out of a hotel window.
Lower rates of REM sleep have previously been linked with a greater risk for mortality and higher rates of emotional issues. A higher number of REM sleep interruptions over the course of a night may also play a role in certain types of insomnia.
Drews thinks the early evolution of primate sleep patterns may offer insight into the importance of REM sleep for fulfilling both physical and emotional needs. "During the evolution of primates, sleep duration was cut further. But the REM sleep total duration in humans stayed about the same," he said. Today, Drews added, "Humans are the primates with the highest percentage of REM sleep."
Drews and his co-author relied on the Sleep Heart Health Study, an American longitudinal study that aimed to identify connections between sleep disorders and cardiovascular disease, stroke and other causes of mortality. The data they used in this new analysis were gathered during the late 1990s and tested subjects using an at-home sleep monitoring system, to prevent potential discomfort or sleep changes that could be triggered by a laboratory setting.
Although the original study had a sample size of around 5,800 people, the NTNU scientists instead examined a smaller subset of people — 69 married individuals and 69 people who had never married — who shared similar demographic and health characteristics. The study did not identify people who were married yet do not sleep with their spouse, and it did not assess marital quality, menopausal status and work status alongside co-sleeping habits, suggesting that future research might benefit from considering those factors.
Married individuals had roughly 10% more REM sleep than non-married individuals, according to Drews. In addition, married people had longer overall durations of REM sleep as well as a higher percentage of REM sleep compared to other stages. Drews noted that although this increase may appear modest, REM sleep could have cumulative effects, meaning that even small changes in the length of REM sleep over months or years may have a significant impact on an individual's mental and physical health.
In future research, Drews hopes to learn how the dynamics of a relationship may play a role in a couple's REM sleep patterns. These explorations could help us better understand "how the quality of the relationship or the attachment style — how those factors play into [sleep]," said Drews. "It's a well-known fact that people who are in good relationships have less mental distress, fewer incidences of mental disorders. They live longer. And of course, it's probably ... multiple factors playing into this, but REM sleep could be definitely one of them."
The study "Couple relationships are associated with increased REM sleep — A proof-of-concept analysis of a large dataset using ambulatory polysomnography" published May 10 in Frontiers in Psychiatry, was authored by Henning Johannes Drews, Norwegian University of Science and Technology and Christian-Albrechts-University; and Annika Drews, SINTEF Ocean AS.