Variations in sleep duration and timing: weekday and seasonal variations in sleep are common in an analysis of 73 million nights from an objective sleep tracker

Study Objectives: Irregular sleep is a major risk factor for adverse health. In a global sample with technology-enabled long-term objective sleep data spanning 3.5 years, we investigated variability in sleep duration and timing over weekdays, months, seasons, and years. Methods: Registered users of an FDA-cleared under-mattress sleep sensor who had ≥28 nights of sleep recordings and averaged ≥4 nights per/week between January 2020 and September 2023 were included for analyses. Generalized nonlinear fixed effects models were used to assess associations between sleep duration and sleep timing with weekday, month, season, and year. Sub-group analyses were conducted by age, sex, and location. Results: Data from 116 879 adults (90 333 males, 26 546 females) aged 49 ± 14 years were analyzed. Weekday variation was observed, with 20–35 minutes longer sleep duration on weekends versus weekdays. Time to bed and time out of bed were 30–40 minutes and 60–80 minutes later on weekends, respectively. Seasonal variation in sleep duration was also evident; sleep duration was 15–20 minutes longer during winter in the northern hemisphere, 15–20 minutes shorter during summer in the southern hemisphere, and variations reduced closer to the equator. Sleep duration decreased from 2020 to 2023 but the effect was small (2.5 minutes). Conclusions: These novel findings underscore the seasonal nature of human sleep, influenced by demographics and geography.