0189 Physiological Effects of Co-Sleeping: A Large-Scale Analysis of Partner Influence on Sleep Composition and Cardiovascular Recovery

Abstract Introduction Co-sleeping is common among adults; however, the physiological effects remain poorly quantified at scale. Prior at-home studies rely on self-report, while existing in-lab studies are limited to < 25 participants. The Eight Sleep Pod (Pod), a smart mattress cover that tracks biometrics for each side of the bed, provides a unique opportunity to evaluate partner-sleep effects using large-scale real-world data. Methods We retrospectively analyzed 4,043 adults (2,189 female; 1,854 male) across 238,288 nights of sleep between August and November 2025. The Pod objectively detects partner presence, heart rate (HR), heart rate variability (HRV), total sleep time (TST), sleep stages, and snoring. Members in this dataset were required to have ≥10 partner nights and ≥10 solo nights. Partner-solo differences were assessed using FDR-corrected paired t-tests, sex effects with Welch’s t-tests, and Pearson correlations assessed relationships between co-sleeping frequency and objective changes. All data below are reported as means ± SD with Cohen’s d effect sizes. Results In this dataset, members slept with their partner on average for 67% ± 18% of nights. Sleeping with a partner increased HRV by 8.0% (+2.5 ± 7.0 ms, d = 0.36) and total sleep time by 1.8% (+6.39 ± 34.78 min, d = 0.18; both P< 0.001). Women showed larger HRV improvements than men when co-sleeping (+10.2 ± 18.2% vs. +5.5 ± 15.3%, respectively; d = 0.20; p < 0.001). Overall changes in HR, sleep stages, and snoring were all statistically significant (P< 0.01), but not physiologically meaningful (e.g., < 1 bpm change in heart rate or < 2% change in sleep stages). The percentage of days spent co-sleeping did not modify outcomes. Conclusion Co-sleeping enhances HRV, and modestly increases total sleep time. Women show larger HRV gains when co-sleeping, suggesting women might experience a larger parasympathetic effect when their partner is near. Future studies should explore why women benefit from co-sleeping more than men, and how age, relationship stability, and relationship duration shape these effects. Support (if any) Eight Sleep Inc. funded this research.