For most couples on the relationship escalator, there's an unspoken assumption that at some point one person's bed will become a shared possession.
As common as this practice is, we're still not sure if this win for snuggles is a loss for sleep. This study could help answer that question once and for all. At least for some.
It's not that nobody has looked into the question. There have certainly been plenty of studies, at least when it comes to one-on-one heteronormative sleep constellations.
The problem is some find co-sleeping leads to more sleep disturbances. Others have found men get more sleep than their partner. It's a mess!
New research conducted by scientists from Germany, Denmark, and the US has pulled out all the stops to provide a broad range of measures detailing sleep quality.
According to psychiatrist Henning Johannes Drews from the Center for Integrative Psychiatry, their "very exact, detailed and comprehensive method to capture sleep on many levels" suggests co-sleeping does wonders for getting a good rest.
For four nights over two consecutive weekends, a dozen healthy heterosexual couples aged between 18 and 29 bedded down either with their partner or on their lonesome.
The volunteers all answered questionnaires about their relationships before turning in for the night, including a quiz that took stock of their respective passion for their partner.
Then it was lights off and wires on for a long night of measuring brain waves, heart activity, movement, and muscle tension.
All of that data added up to a fairly clear indication that sleeping together was associated with 10 percent more of the deep, refreshing loss of consciousness called Rapid Eye Movement (REM) sleep.
This state of solid rest generally kicks in around an hour and a half after you nod off, and comes with your own private nocturnal show time called dreaming.
Not only is it entertaining to try to remember the next day, this kind of dream sleep is gold dust for consolidating memories, while boosting the regulation of emotions and enhancing social connections.
In other words, while having a nap or two might make you feel energised, getting plenty of REM sleep is vital for keeping your brain in top working order.
They also found that the couple's sleep cycles fell into synch. This was especially true for those evaluated to be in a deeply loving relationship.
Sleeping together did seem to cause each partner's body to kick around a little more than usual, but the increased movement didn't seem to interfere with sleep quality in any appreciable way.
The study didn't go so far as to link these positive effects with their volunteer's experiences. But the fact they had improved sleep quality is a fairly convincing sign that for many couples, having a partner close at night is better than going solo.
All of that said, there is a sizeable list of caveats to note before purchasing that queen size ensemble.
There were just 24 individuals involved in the study, all young and healthy with no sleep apnea or other sleep disturbing concerns. They also happened to co-sleep already, ruling out individuals who prefer keeping to their own bed, or those just not used to sleeping with others.
Studying sleep patterns in a specially designed laboratory could also introduce confounding factors that make it hard to interpret the results for a more 'natural' setting.
Lastly there is the fact just one kind of relationship is represented by the sample.
So if you're young, healthy, hetero and happy to share a bed – and have a thing for snuggling up in a sleep laboratory – your brain could thank you for having a loving partner nearby when you drift off to la-la land.
For the rest of us, there's always the couch.
This research was published in Frontiers in Psychiatry.