Abstract
Previous studies of seasonal effects on sleep have yielded unclear results, likely due to methodological differences and limitations in data size and/or quality. We measured the sleep habits of 216 individuals across the U.S. over four seasons for slightly over a year using objective, continuous, and unobtrusive measures of sleep and local weather. In addition, we controlled for demographics and trait-like constructs previously identified to correlate with sleep behavior. We investigated seasonal and weather effects of sleep duration, bedtime, and wake time. We found several small but statistically significant effects of seasonal and weather effects on sleep patterns. We observe the strongest seasonal effects for wake time and sleep duration, especially during the spring season: wake times are earlier, and sleep duration decreases (compared to the reference season winter). Sleep duration also modestly decreases when day lengths get longer (between the winter and summer solstice). Bedtimes and wake times tend to be slightly later as outdoor temperature increases.
Highlights
Sleep is vital to health[1,2,3,4], mood[5,6,7,8,9], cognitive performance[10,11,12], work quality[13,14,15,16], and social life[17,18,19,20]
It is clear that artificial light interacts with circadian systems[73,74,75,76], but it is unclear if artificial light suppresses[77] or interacts[78] with seasonal variations in circadian mechanisms, and further, if these effects result in observed seasonal variations in sleep parameters such as sleep duration[79]
We investigated every extra hour of day length associated with a decrease in sleep duration of 3.6 min (95% C.I. (−2.4, −4.8), P < .001)
Summary
Sleep is vital to health[1,2,3,4], mood[5,6,7,8,9], cognitive performance[10,11,12], work quality[13,14,15,16], and social life[17,18,19,20]. Circadian systems rely on internal timekeeping cells[44] These “clock cells” synchronize with the environment via “zeitgebers”[45] or “time clues” such as light and ambient temperature and serve as a circadian pacemaker to coordinate other circadian responses to optimize to the environment[46,47,48,49,50,51,52,53], e.g., in humans to promote sleep when it is dark and to be awake when it is light, to be asleep at the lowest point of core body temperature[43,54,55,56], and/or to avoid extremes in ambient temperature that can impair sleep[57,58,59,60,61]. It is clear that artificial light interacts with circadian systems[73,74,75,76] (for a review, see Duffy and Wright52), but it is unclear if artificial light suppresses[77] or interacts[78] with seasonal variations in circadian mechanisms, and further, if these effects result in observed seasonal variations in sleep parameters such as sleep duration[79]
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