Sleep and Overnight Cardiovascular Outcomes During the First Week on a Temperature-Controlled Sleep Surface: Stratified by Baseline Performance

Temperature-controlled sleep surfaces are used nightly by hundreds of thousands of people. Despite mass adoption, subjective reports of sleep quality have not yet been substantiated with objective measurements; whether differences in individual baseline sleep contribute to overall efficacy remains unknown. Cohort means aggregate individuals with qualitatively different sleep deficits, and a benefit concentrated in the impaired can vanish when averaged against those already sleeping well. In an open-label study of 171 adults, we examined wearable-derived sleep and overnight cardiovascular endpoints during programmed change of a thermal-controlled sleep surface across seven baseline and seven thermally regulated nights. Participants were classified on baseline performance, separately for each endpoint, rather than averaged as a single group. Cohort-wide, total sleep time increased 7.3 minutes (95% CI 1.7 to 12.8, p = 0.010), average nocturnal heart rate fell 1.79 bpm and minimum heart rate 1.75 bpm (both p < 0.001), and heart rate variability rose 3.25 ms (p = 0.001). Stratification revealed a baseline-dependent pattern. The most-deficient quartile gained 9.6% in total sleep time, 19.4% in REM, 13.1% in deep sleep, and 15.6% in HRV, all p < 0.001, and wake after sleep onset fell 26% in the most fragmented quartile (-16.3 minutes, p < 0.001). Objective gains were largest where the baseline deficit was greatest. Controlled trials are needed to validate these findings.