LAUSR

Light is the most powerful zeitgeber influencing sleep-wake patterns, and winter’s shorter days have profound effects on mood, energy, and metabolic function. Here, we leverage big data from consumer sleep technology to examine the relationship between objectively measured sleep in winter versus summer months in the United States. The dataset included 21,101 users residing in the US across 1,255,518 nights (age range: 17-90, mean age: 46.6 ± 16.7 years, 59% female). Data were extracted from 01 January 2019 until 31 August 2022. Seasons were defined according to the Northern Hemisphere’s meteorological calendar and included winter (December - February) and summer (June - August). USA public holidays were mapped and removed from the data. The relationships between objectively measured sleep and winter versus summer were examined using linear regression models, controlling for age and gender. A shift to later average monthly wake times were observed in both summer and winter, peaking in summer. Similarly, bedtimes shift later in summer and winter, yet the shift in summer was greater than winter (winter vs summer: waketime: 07:06 vs 07:07, ß = -0.46, SE = 0.023, p< 0.001, bedtime: 23:17 vs 23:23, ß = 0.12, SE = 0.006, p< 0.001). Although bedtime and wake times delay during the winter and summer seasons, measures of sleep health including sleep duration, sleep efficiency, and SleepScore peak in winter and slowly decline to their lowest point during the summer months (winter vs. summer: SleepScore 78.4 vs 77.6, ß = -0.89, SE = 0.17, p< 0.001; sleep duration 359.6 min vs 352.8 min, ß = -4.8, SE = 1.02, p< 0.001; sleep efficiency 77.5 vs 76.6, ß = 0.86, SE = 0.038, p< 0.001). Bedtime and wake time delays were greater in summer than winter, likely contributing to small improvements to sleep quality, duration, and efficiency in winter compared to summer. These findings are generally supported by previous research examining sleep-wake patterns in locations with extreme seasonal differences, such as Northern Norway, where, despite midnight sun and polar nights, researchers have found little variation in sleep-wake timing. SleepScore Labs