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Human Sleep Timing in Late Autumn and Late Spring Associates with Light Exposure Rather than Sun Time in College Students

Shochat, Tamar, Santhi, Nayantara, Herer, Paula, Flavell, Sapphira A., Skeldon, Anne C. and Dijk, Derk-Jan (2019) Human Sleep Timing in Late Autumn and Late Spring Associates with Light Exposure Rather than Sun Time in College Students Frontiers in Neuroscience.

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Abstract

Timing of the human sleep-wake cycle is determined by social constraints, biological processes (sleep homeostasis and circadian rhythmicity) and environmental factors, particularly natural and electrical light exposure. To what extent seasonal changes in the light-dark cycle affect sleep timing and how this varies between weekdays and weekends has not been firmly established. We examined sleep and activity patterns during weekdays and weekends in late autumn (standard time, ST) and late spring (daylight saving time, DST), and expressed their timing in relation to three environmental reference points: clock-time, solar noon (SN), which occurs one clock hour later during DST than ST, and the midpoint of accumulated light exposure (50%-LE). Observed sleep timing data were compared to simulated data from a mathematical model for the effects of light on the circadian and homeostatic regulation of sleep. A total of 715 days of sleep timing and light exposure were recorded in 19 undergraduates in a repeated-measures observational study. During each three-week assessment, light and activity were monitored, and self-reported bed and wake times were collected. Light exposure was higher in spring than in autumn. 50%-LE did not vary across season, but occurred later on weekends compared to weekdays. Relative to clock-time, bedtime, wake-time, mid-sleep, and midpoint of activity were later on weekends but did not differ across seasons. Relative to SN, sleep and activity measures were earlier in spring than in autumn. Relative to 50%-LE, only wake-time and mid-sleep were later on weekends, with no seasonal differences. Individual differences in mid-sleep did not correlate with SN but correlated with 50%-LE. Individuals with different habitual bedtimes responded similarly to seasonal changes. Model simulations showed that light exposure patterns are sufficient to explain sleep timing in spring but less so in autumn. The findings indicate that during autumn and spring, the timing of sleep associates with actual light exposure rather than sun time as indexed by SN.

Item Type: Article
Divisions : Faculty of Health and Medical Sciences > School of Biosciences and Medicine
Authors :
NameEmailORCID
Shochat, Tamar
Santhi, NayantaraN.Santhi@surrey.ac.uk
Herer, Paula
Flavell, Sapphira A.
Skeldon, Anne C.A.Skeldon@surrey.ac.uk
Dijk, Derk-JanD.J.Dijk@surrey.ac.uk
Date : 2019
DOI : 10.3389/fnins.2019.00882
Copyright Disclaimer : © 2019 Shochat, Santhi, Herer, Flavell, Skeldon and Dijk. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.
Uncontrolled Keywords : Light; Circadian; Sleep; Mathematical modelling; Entrainment; Chronotype
Depositing User : Clive Harris
Date Deposited : 16 Aug 2019 08:25
Last Modified : 16 Aug 2019 08:25
URI: http://epubs.surrey.ac.uk/id/eprint/852420

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