0366 Active Temperature Regulation During Sleep Improves Circadian Rhythm, Sleep Composition, and Cardiovascular Recovery in Older Adults

Abstract Introduction Sleep quality declines with age, potentially resulting from a blunted circadian rhythm of core body temperature (Tc), which can reduce deep sleep and cardiovascular recovery. Cooling during early hours of sleep with high-heat capacity mattresses lowers Tc and heart rate (HR) and increases deep sleep in postmenopausal women, suggesting whole-night active temperature regulation (ATR) might further enhance Tc rhythms and sleep-related cardiovascular recovery. We evaluated how continuous ATR affects circadian rhythm, cardiovascular recovery, and sleep composition in older adults. Methods 90 participants (n=60 postmenopausal women and n=30 age-matched men; mean±SD: 55±5 y) slept on the Eight Sleep Pod, a mattress cover enabling ATR throughout the night, for 7 nights each with ATR OFF vs. ON. Sleep stages, HR, and heart rate variability (HRV) were measured nightly with smart rings, and Tc was measured via gastrointestinal pills. Linear mixed-effects models analyzed nightly outcomes (means±SE reported below), Pearson's correlation coefficient and linear models analyzed participant-level changes between ATR conditions, and single-harmonic cosinor analysis analyzed Tc rhythms. Results On average, ATR decreased sleeping HR by 3% (-1.8±0.3 bpm), increased HRV by 11% (+3.6±0.6 ms), and reduced Tc by -0.16±0.01°C. ATR ON lowered Tc mesor, the 24-hour average, by -0.07±0.01°C and increased Tc amplitude by +0.07±0.02°C (all P< 0.001), indicating improved circadian rhythm. Larger decreases in Tc from ATR OFF to ON correlated with greater HR improvements (r=0.34, P=0.037). Using cooler ATR temperatures corresponded with larger HRV increases (r=-0.31, P=0.004). ATR ON improved sleep composition for participants with poor sleep composition at baseline (i.e., average light sleep >65.0%, deep sleep < 13.7%, REM sleep < 21.3% or wake after sleep onset >9.5%; all P< 0.05). Conclusion To our knowledge, this is the first evidence that ATR can lower Tc in adults 55+ years, thereby improving Tc circadian rhythm. These circadian-rhythm improvements enhanced cardiovascular recovery and sleep composition. As sleep quality is reduced with aging, ATR during sleep can be an excellent non-pharmacological solution to restore sleep health in older adults. Support (if any) This research was funded by Eight Sleep Inc.