0034 The Social Side of Sleep: Chronotype, Co-Sleeping, and Relationship Health

Abstract Introduction Sleep and social connectedness are closely linked, and prior studies show that relationship functioning relates to both sleep quality and feelings of loneliness. Nocturnal loneliness—loneliness experienced at night—has been associated with poorer sleep and emotional well-being, yet little is known about couple-level contributors. Chronotype mismatch may be one such factor, as misaligned sleep–wake preferences can disrupt shared routines and interpersonal synchrony. We therefore examined whether chronotype mismatch within married couples is associated with higher nocturnal loneliness and poorer relationship quality. Methods Participants with a bed partner in the NOLO Survey Study (N=254) were recruited through Prolific and completed measures of demographics: age (M=47±14), sex (51% female), race (76% White), education (34% Bachelor’s degree), marital status (73% married), and number of cosleeping nights, chronotype: chronotype of self and partner (morning, intermediate, evening) and the Morningness-Eveningness Questionnaire (MEQ), nocturnal loneliness: Nocturnal Loneliness Scale (NLS), relationship quality: Quality of Marriage Inventory scale for Relationship Quality (RQ), and self-reported ratings of mental, physical, and sleep health (0-100, with higher scores indicating better health for each). Six chronotype match groups based on self/partner category were created. We used Spearman’s correlation coefficient to determine how chronotype, health, RQ, and NLS were related. Results Having evening chronotype and lower co-sleeping frequency were associated with poorer mental, physical, and sleep health, ρ=.15-33, p=.05-.001, for all. Having a bed partner with evening chronotype was significantly related to the participant having poorer physical and sleep health, ρ=.13, p<.05, for both. Higher QR scores correlated with better mental health, ρ=.20, p=.002. Chronotype matching between partners was not significantly associated with any health outcome. Conclusion Overall, results indicate that evening chronotype and reduced co-sleeping frequency contribute more to poorer health and relationship functioning than chronotype similarity within couples. Chronotype matching did not explain differences in nocturnal loneliness or relationship quality, suggesting that individual sleep–wake preferences, rather than partner alignment, may be the more meaningful driver of well-being. These findings highlight the importance of considering chronotype as an individual risk factor within couple contexts. Support (if any)