😴 Do you sleep better next to your partner—or on your own? The "sleep divorce" trend is sweeping the globe, with couples choosing separate beds for better rest. Now, a University of Tokyo mouse study has tackled this question scientifically— and the answer turns out to depend on who you are.
What Is "Sleep Divorce"? A Growing Global Trend
"Sleep divorce" is the practice of couples deliberately sleeping in separate beds or bedrooms to improve sleep quality. Despite the dramatic name, it is a practical, positive choice that more and more people are making worldwide.
A 2025 survey by the American Academy of Sleep Medicine found that 31% of U.S. adults have opted for some form of sleep divorce, with the figure climbing to 39% among 35- to 44-year-olds. In the UK, roughly one in five couples now sleep apart regularly, and a similar trend is unfolding across much of the developed world.
Japan is no exception. A survey by Koala Sleep Japan found that over 30% of Japanese couples sleep in separate rooms. With more than 70% of Japanese couples being dual-income, shift work and differing schedules make shared sleep particularly challenging. Japanese culture also has a long tradition of "co-sleeping in a row" (kawa no ji—literally "sleeping like the character 川"), where the whole family shares a room, but this practice is evolving rapidly.
The most common reasons for sleep divorce include snoring, restlessness, different sleep schedules, and conflicting temperature preferences.
The University of Tokyo's Breakthrough Mouse Experiment
Against this backdrop, a research team at the University of Tokyo published a fascinating paper in Scientific Reports in February 2025, asking: How does social connection itself—separate from physical contact—affect sleep quality?
A Novel Approach: "Neighbor Housing"
Previous animal studies comparing group housing and solitary housing could not separate the effects of physical disturbances (fighting, jostling) from the effects of social connection itself. To solve this, the Tokyo team devised "neighbor housing"—placing mice in the same cage but separated by a transparent acrylic divider. The mice could see and smell each other but couldn't physically interact. Think of it as living next door with a glass wall.
After a period in this neighbor housing, mice were moved to solitary housing, and their brain waves were measured to assess sleep quality in detail.
The Surprise: Social Rank Flips the Result
The mice had established social hierarchies—dominant (alpha) and subordinate individuals. During neighbor housing, both groups showed similar sleep durations and REM sleep amounts.
But when switched to sleeping alone, the results diverged dramatically:
- Dominant mice showed improved sleep quality—deeper non-REM sleep and better REM sleep brainwave patterns
- Subordinate mice experienced the opposite—their sleep quality declined
The researchers interpreted this as follows: for dominant mice, the presence of others kept them in a state of heightened alertness, and solitude allowed them to finally achieve optimal sleep. For subordinate mice, the comfort of having others nearby provided a sense of security, and losing that social connection caused isolation stress that degraded their sleep.
Genetics Matter Too
The team also compared different genetic strains of mice. In the commonly used B6 strain, subordinate mice showed increased REM sleep after the switch to solitary housing. However, in the F1 strain—which forms stronger, more rigid social hierarchies—no such change was observed. This suggests that even under identical social conditions, your genetic makeup influences how your sleep responds.
What Does This Mean for Humans? Pros and Cons of Co-Sleeping vs. Sleeping Alone
While we can't directly apply mouse results to humans, this research powerfully suggests that the optimal sleep environment differs from person to person. Combined with existing human research, here is a balanced look at the trade-offs.
Benefits of Co-Sleeping
- Security and oxytocin: Physical closeness promotes the release of oxytocin (the "love hormone"), reducing anxiety and helping you relax into sleep
- More sleep overall: A 2022 large-scale study found that frequent bed-sharers slept about 15 minutes more per night and had lower insomnia severity
- Relationship bonding: Before-bed conversations and physical closeness strengthen relationship satisfaction
- Health monitoring: Partners often detect sleep disorders like sleep apnea before the person themselves notices
Drawbacks of Co-Sleeping
- Disruptions from snoring and movement: A 2025 global sleep survey found one in three couples are disturbed by a partner's noise. Women are disproportionately affected—20% report nightly disruptions versus 11% of men
- Conflicting environmental preferences: Temperature, lighting, mattress firmness, and blanket habits vary widely between individuals
- Mismatched schedules: Morning people and night owls can clash badly when forced to share a sleep schedule
Benefits of Sleeping Alone
- Major sleep quality gains: A SleepFoundation.org survey found 52.9% of sleep divorcees reported improved sleep quality, averaging 37 extra minutes of sleep per night
- Reduced stress: 60% of couples who sleep separately report lower stress levels
- Full customization: You can optimize your room temperature, lighting, noise level, and bedding entirely for yourself
Drawbacks of Sleeping Alone
- Social isolation stress: As the Tokyo study showed, some individuals experience stress when separated, losing the comfort of another's presence
- Intimacy risk: Without deliberate effort to maintain connection, couples may drift apart emotionally
- Housing constraints: Especially in Japan, where living spaces tend to be compact, having a spare bedroom is a luxury many cannot afford
The Bigger Picture
The University of Tokyo's research demonstrates that sleep quality is not simply about "together or alone" but is regulated by a complex interplay of social rank, genetic predisposition, and psychological security.
Translated into human terms, this means there are "people who sleep better with someone nearby" and "people who sleep better with personal space"—and science now has evidence to back up both sides.
The key takeaway: don't be trapped by the belief that "couples must share a bed" or that "sleeping apart means a troubled relationship." Instead, find what works best for both your sleep and your partnership. The term "sleep divorce" may sound alarming, but for many, it's actually a "sleep alliance"—a deliberate choice that makes both partners happier, healthier, and more rested.
In Japan, the family tradition of sleeping together in a row (kawa no ji) is deeply rooted, but "sleep divorce" is gaining acceptance as a practical solution. What about in your country? Do couples always share a bed, or is sleeping apart becoming more common? We'd love to hear about the sleep culture where you live!
References
Reactions in Japan
My husband's snoring was hellish, but I endured it thinking 'couples should sleep together.' Reading this study, I feel relieved that I don't need to feel guilty about sleeping apart.
The 'neighbor housing' concept is brilliant. An experimental design separating physical contact from social connection—seems obvious yet nobody had done it. Impressive work from the Hayashi Lab.
We naturally ended up in separate rooms after 15 years of marriage. Felt guilty at first, but we're both in better moods in the morning and actually get along better. Feels like science is finally catching up.
Dominant mice sleep better alone, subordinate mice sleep better with company—this maps onto human marriage dynamics a bit too accurately. Can't even laugh.
Some of my clients cry when I tell them 'it's okay to sleep separately.' This study provides evidence I can use in my sleep coaching practice. Very grateful for it.
Applying mouse experiments to humans is a stretch. Humans have too many variables mice don't—scrolling phones in bed, fighting over blankets, etc.
As a dad sandwiched between two kids in the 'kawa-no-ji' formation, I'm not in a sleep divorce—I'm in a sleep sandwich. I'd probably cry if I ever got to sleep alone.
The name 'sleep divorce' is terrible. We're not fighting—but the word 'divorce' makes people judge us. How about 'sleep separation' instead?
The finding that REM sleep is regulated by both social hierarchy and genetic background is clinically significant. It reinforces the need to assess patients' living environments alongside their sleep disorders.
Sleeping with 3 cats is basically this experiment. The cats are dominant and I'm subordinate. They roam freely while I can't move. But I'm happy, so who cares about sleep quality.
A separate room is a luxury in Japanese housing. We live in a 1LDK (one-bedroom apartment), so it's physically impossible. Forget the study, just give us more rooms.
The link between elderly solitary living and sleep quality is a serious issue. Insomnia after losing a spouse may be exactly the 'subordinate mouse' response. This connects to loneliness and sleep research.
Working three rotating shifts, my schedule is completely out of sync with my husband's. We've been in separate rooms for 3 years. Felt guilty, but this article helps me own our style.
If genetic background changes the sleep impact, could genetic testing one day tell you 'you're the type who sleeps better together' vs 'you're the solo sleeper type'?
We're newlyweds so we cuddle every night, but I'm not sure we'll be like this in 10 years. This study helps me accept that it's okay if things change.
Sleep divorce is fully mainstream in the US now. Cameron Diaz going public really lowered the barrier. The Tokyo study showing differences based on social rank is fresh—it connects to power dynamics within couples too.
In Sweden we value personal space, so sleeping apart isn't stigmatized. I actually find the Tokyo study's proof of 'security from being together' more interesting. Curious how Nordic individualism affects sleep patterns.
In India, it's normal for multiple family members to share one room. 'Sleep divorce' sounds like a luxury concept. But the finding that subordinate individuals sleep better with company might actually validate our cultural wisdom.
As a Frenchman, sleep divorce doesn't sound very romantic—but historically, French aristocrats always had separate bedrooms. Turns out it was scientifically rational too. The genetic background finding is especially fascinating.
If I told my Polish grandmother that couples sleep apart, she'd clutch her cross. The cultural taboo is still strong. But scientific data might help start intergenerational conversations about it.
In Korea, 'sumyeon ihon (sleep divorce)' is also trending. Like Japan, our homes are small so it's hard to practice, but this mouse study shows the importance of recognizing individual differences. The battle against a husband's snoring is truly universal lol.
I run a sleep clinic in the UK. The finding that dominant individuals sleep better alone while subordinate ones benefit from company could relate to patient personality traits. Looking forward to clinical applications.
In Mexico, family bonds are everything. Sleeping apart as a couple is unthinkable and would start neighborhood gossip. But honestly, my husband's sleep movements are awful and I wake up aching. If science can break cultural taboos, I welcome it.
This topic itself is sensitive in the Middle East. But reading it as scientific research, the finding about genetic background influencing sleep responses has cross-cultural value. I'd like to see studies with more diverse genetic backgrounds.
Russian apartments are small, so there's no choice. In the Soviet era, a whole family in one room was normal. But younger generations now crave personal space. This study might support that shift.
I work for a bedding company in Australia. Sales of motion-isolation mattresses are growing yearly—a third option where you sleep together while getting sleep divorce benefits. Technology can solve part of this.
In Ghana, couples sharing a bed is the default. But on hot nights, even body contact is uncomfortable. The Tokyo study scientifically demonstrating 'individual differences in comfort' is relevant even in African climate conditions.
I'm a sleep researcher in Brazil. The finding that REM sleep changes through interaction between social hierarchy and genetics is elegant. However, mouse social structures and human couple dynamics are qualitatively different—we should be cautious about overgeneralization.
In Taiwan, 'fen fang shui (sleeping in separate rooms)' is trending. The Tokyo study is interesting, but given Taiwan's housing prices, a separate room is a pipe dream. Let us afford a house first.
In the Netherlands, practical solutions are preferred, so there's little stigma around sleep divorce. But the most interesting part of this study is 'there's no single answer.' Science that recognizes individual differences is wonderful.