Sex differences in the reactions to sleeping in pairs versus sleeping alone in humans

Couples sleeping in pairs is a modern phenomenon with potential side-effects on sleep structure and circadian rhythms. In order to examine its effects, 10 healthy heterosexual couples with stable relationships who regularly sleep apart or together in their home environments were recruited. The participants were asked to spend at least 10 nights alone and 10 nights together over the course of the study. Their sleep was monitored over 28 days in their homes with actigraphic techniques and sleep diaries. Group analyses were performed on their sleep efficiency and subjective sleep quality according to sleep condition. The daily variations in sleep fragmentation indices of the partners were used as a measure of their nocturnal activity synchronization. Sharing a sleeping space with a partner had negative effects on sleep in women, as documented in the actigraphic measurements of sleep efficiency and subjective assessments of sleep and awakening quality. Sexual contact mitigated the negative subjective report, without changing the objective results. Subjective assessments of sleep quality were lower in men than women when sleeping alone. They increased to the same level as women while sleeping in pairs with or without sexual contact. The sleep efficiency in men was not reduced by the presence of their partner unless sexual contact occurred. Analyses of sleep fragmentation showed that there was no synchronization of deviation from the norm levels between the partners on individual nights either when they slept alone or in couples. The sex differences in the nocturnal sleep reactions to partner presence may be attributed to sex-specific behavioral traits associated with cultural norms or parenting in women and the desire for group sleep in men