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To sleep alone or share your bed? According to one new study, guys who claim they “sleep better alone” may want to come up with a new line. Men, the study suggests, get better sleep when they spend the night cuddling up. The same isn't true for women.

Research on couple co-sleeping is hardly fresh, but most studies concern older couples in the bedroom. While they tend to report sleeping better beside their loved ones, physiological sleep activity tests generally suggest the opposite — sleeping with partners is associated with decreased deep sleep and more bodily movement, especially for women. But what about less-established couples who don’t share bedrooms — the lovebirds who’ve just recently defined the relationship, or Saturday-night soulmates hesitant to use labels? Psychologists at Germany's Freiberg University sought to see how and how well younger couples sleep when they share the covers or bid adieu at bedtime. 

For the study, published in the journal Behavioral Sleep Medicine, researchers asked 15 twenty-something heterosexual couples who didn’t live together to keep sleep diaries and wear activity-monitoring bracelets for five consecutive nights. Over the course of the experiment, each couple had to sleep together and alone, in both their own bed and their partner’s bed, yielding four distinct setups.

Ready access to a cuddle-partner did matter, at least for men, who slept substantially longer and later when they curled up alongside their girlfriends.

Researchers compared participants’ subjective rest-assessments to data on bed times, waking times, mid-sleep awakenings and quality and duration of sleep. Ultimately, they wanted to see how location (her apartment or his) and setting (sleeping apart or together) affected sleep in couples.

In this case, location didn't matter — couples slept just as well in their partners’ beds as in their own. But, sleeping next to a cuddle-partner did matter, at least for men, who slept substantially longer and later when they curled up alongside their girlfriends. While both male and female participants reported sleeping better in pairs, the actigraphy data said otherwise. Women got the same quality sleep with or without their boyfriends hogging the covers.

It was surprising, researchers wrote, that sleeping in pairs affected men, and only men, so strongly.

It has been argued that co-sleeping leads to better, longer sleep because people feel more emotionally and physically secure. And, from an evolutionary standpoint, the effect should arguably be more pronounced in women who, given their smaller muscles, need more protection. But, the growing evidence suggests that sleeping in pairs disturbs women’s sleep more than men’s. Why? Perhaps, the study says, because men are far more likely to have sleep apnea. All that disordered nocturnal breathing keeps women up — snoring and snoozing don’t make for compatible bedfellows.