Sleeping with a partner affects your sleep cycle in one striking way – study

Sleeping with a partner requires navigating cover sharing, different bedtimes, and changing wakeup schedules. New research suggests that the trials of sharing a bed are actually worth it, especially when you both doze off.

In a sample of 12 heterosexual couples who have been a couple for an average of 23.5 years, scientists found that sleeping together was linked to 10 percent more REM sleep compared to sleeping apart. During REM sleep, processes like dreaming and memory consolidation kick into gear. Co-sleepers also had longer, undisturbed fragments of REM sleep when they slept together.

The nights weren't particularly tranquil: The couples also moved more when they slept together compared to when each person slept alone. But despite that discombobulation, they entered sleep stages at roughly the same time.

When partners slept apart they spent about 36.6 percent of the night, moving through sleep stages at the same time. Because all humans cycle through sleep stages, that's not especially surprising — there's naturally going to be a little overlap.

What's notable is that this overlap significantly increased when the couples slept together, growing to 46.9 percent.

The study was published Thursday in Frontiers in Psychiatry.

Henning Johannes Drews is the study's lead author and a postdoctoral researcher at the Center for Integrative Psychiatry in Germany. He explains that these findings are a departure from conventional wisdom and previous research on sleeping with a partner.

"There is – even in the medical community – the notion that if you sleep with a partner, you might subjectively think that you slept well or better, but objectively, your sleep is more disturbed," Drews tells Inverse. "I would like people to take away that if you want to share a bed with your partner, there is nothing to be said against it.

"It might even be very good for you due to the REM-sleep stabilization."

A night in the sleep lab – This study tackles the perils of sleeping together with polysomnography, a type of sleep study that records brain waves, movement, oxygen levels in blood. That means that couples had to sleep in a lab while monitored by scientists (not the most natural place to tuck into bed with your partner).

Couples slept in the lab for four nights over two weekends. One weekend, they slept in two separate rooms in single beds. The next weekend, they slept in one room in two beds pushed together. They were given two sets of sheets and two blankets – so cover hogging likely wasn't a huge factor here.

When couples slept together, they told scientists that their sleep quality improved. Yet the scientists found no differences in measures like total sleep time, or how long it took people to fall asleep. They did find increases in the amount of REM sleep itself and the architecture of that REM sleep.

When couples slept together there were, on average, 5.4 REM disruptions during the night. When they slept apart there 8.5 REM sleep disruptions. That translated to longer uninterrupted REM sleep periods — they lasted on average about 22 minutes when partners slept together compared to13.4 when they slept apart. Still, this measure varied a lot by study subject, so it's not a perfect comparison.

Drews has two working explanations for the reduction of REM sleep disruptions. The first is purely biological. During REM sleep the body's ability to regulate temperature is impaired. A partner may help body temperature stay stable, he argues.

The second is psychological: a partner might just make us feel more secure.

"REM sleep is in fact disturbed and reduced by psychosocial stress," says Drews. "Thus, relaxing and safe environments promote REM sleep. The presence of a partner might help to create such a safe environment."

Syncing up sleep – One of the study's more perplexing findings was the emergence of sleep synchronization between partners.

On one hand, that could simply be because partners are simply going to sleep around the same time and being awakened (perhaps by one another) throughout the night, causing them to align.

But even when scientists excluded wake incidents, they still found that 47.5 percent of epochs (small chunks of time within a sleep study that allow scientists to compare stages of sleep) were in sync with one another's.

Right now, Drews suggests that it's the depth of the relationship that might explain why couples tend to sync up when they sleep.

Having a deeper relationship was strongly correlated with this REM sleep synchronization, the study suggests. That's just a trend – it can't be completely confirmed with experimental data.

Because this is a small pilot study, the data isn't precise enough to apply to everyone. It also only looked at healthy, heterosexual couples. As for studies that apply to non-heterosexual couples, Drews says that he's not aware of any papers that use objective sleep measures for homosexual couples yet. Finally, sharing a bed probably not a way to improve your sleep, says Drews, especially if you know you prefer sleeping alone.

This study does suggest that sharing a bed doesn't have to mean missing out on a good night's rest. In some cases, you may yourself more rested the you might expect.

Abstract:

Background/Objectives: Sharing the bed with a partner is common among adults and impacts sleep quality with potential implications for mental health. However, hitherto findings are contradictory and particularly polysomnographic data on co-sleeping couples are extremely rare. The present study aimed to investigate the effects of a bed partner’s presence on individual and dyadic sleep-neurophysiology.

Methods: Young healthy heterosexual couples underwent sleep-lab-based polysomnography of two sleeping arrangements: individual sleep and co-sleep. Individual and dyadic sleep parameters (i.e., synchronization of sleep stages) were collected. The latter were assessed using cross recurrence quantification analysis. Additionally, subjective sleep quality, relationship characteristics, and chronotype were monitored. Data were analyzed comparing co-sleep vs. individual sleep. Interaction effects of the sleeping arrangement with gender, chronotype, or relationship characteristics were moreover tested.

Results: As compared to sleeping individually, co-sleeping was associated with about 10% more REM sleep, less fragmented REM sleep (p=0.008), longer undisturbed REM fragments (p=0.0006), and more limb movements (p=0.007). None of the other sleep stages was significantly altered. Social support interacted with sleeping arrangement in a way that individuals with suboptimal social support showed the biggest impact of the sleeping arrangement on REM sleep. Sleep architectures were more synchronized between partners during co-sleep (p=0.005) even if wake phases were excluded (p=0.022). Moreover, sleep architectures are significantly coupled across a lag of ± 5min. Depth of relationship represented an additional significant main effect regarding synchronization, reflecting a positive association between the two. Neither REM sleep nor synchronization was influenced by gender, chronotype, or other relationship characteristics.

Conclusion: Depending on the sleeping arrangement, couple’s sleep architecture and synchronization show alterations that are modified by relationship characteristics. We discuss that these alterations could be part of a self-enhancing feedback loop of REM sleep and sociality and a mechanism through which sociality prevents mental illness.