Why Co-Sleeping Can Cost Women More Than Men

Rather than a single lab night, this study followed ten couples for 28 nights in their own homes and their own beds, alternating between sleeping together and sleeping apart, using wrist actigraphy to track movement and sleep continuity alongside daily sleep diaries. The result showed a clear asymmetry: women's actigraphically measured sleep efficiency was reduced by their partner's presence, and their own subjective ratings of sleep and morning freshness were worse too. Men's objective sleep efficiency, by contrast, wasn't affected by sleeping next to a partner, though their subjective sleep ratings, generally lower than women's when sleeping alone, improved to match women's once they shared a bed.

With only ten couples, this is a small study, though its 28-night, real-home design is a genuine strength most sleep research lacks. It can't fully explain why the sexes respond differently, the authors point to possible roles for evolved vigilance behaviours in women and a preference for company in men, but as a description of what happens, it's a useful counterweight to the more romantic assumption that sharing a bed is straightforwardly better for everyone. For many women, the data suggests, it measurably isn't, whatever it feels like from the inside.