Seasonal Variation in Sleep, Respiratory, and Cardiovascular Parameters Assessed by a Wearable Device

Seasonal variation in sleep patterns is well recognized in PSG studies and actigraphy, yet few studies have comprehensively examined its impact on both sleep architecture and respiratory physiology using wearable technology. Circadian and environmental cues such as light exposure, temperature, and humidity may modulate sleep quality, apnea severity, and oxygenation, but large-scale, real-world data remain limited. We conducted a retrospective analysis of 2,386 home sleep studies, one study per individual, recorded between 2022 and 2025 using the SleepImage wearable system in Fresno, California. Each study was categorized by season of recording (winter, spring, summer, fall) based on start date. Key outcomes included total sleep duration, sleep latency, wake after sleep onset (WASO), mean and minimum SpO₂, apnea-hypopnea indices (sAHI3%, sAHI4%), respiratory disturbance indices (sRDI3%, sRDI4%), oxygen desaturation indices (ODI3%, ODI4%), and heart rate metrics. Analyses were adjusted for age using analysis of covariance (ANCOVA) and multiple linear regression to evaluate both main and interaction effects (Season × Age). Significant seasonal differences were observed in multiple parameters after adjusting for age. Sleep latency was longest in summer (836.97 ± 1007.76 sec) and shortest in fall (582.51 ± 661.49 sec, p < 0.001). Apnea hypopnea indices were highest in winter and lowest in fall (p = 0.027), while mean SpO₂ and maximum SpO₂ were modestly reduced in colder months (p < 0.001). Mean heart rate was higher in winter (68.3 ± 10.9 bpm) compared with summer (65.7 ± 9.3 bpm, p < 0.001). Interaction models revealed that age modified seasonal effects on sleep efficiency and latency, with older adults showing greater winter-related sleep latency increases but smaller seasonal fluctuations in apnea indices. Sleep and respiratory parameters exhibit distinct seasonal modulation, with winter months associated with higher apnea burden and reduced oxygenation, and summer associated with prolonged sleep latency and greater fragmentation.