Sleep Timing in Late Autumn and Late Spring Associates With Light Exposure Rather Than Sun Time in College Students

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.

Sleep characteristics and cerebrospinal fluid biomarkers of Alzheimer's disease pathology in cognitively intact older adults: The CABLE study

“…Herein, we further provided evidence confirming a nonlinear relationship, with approximate cutoffs, between CSF indicators of Aβ deposition and self‐reported nocturnal sleep duration, but also identified similar trends with bedtime. Notably, it was possible that the “optimal” bedtime might reflect the physiological fluctuation of CSF amyloid proteins and could be influenced by multiple factors in different cohorts, such as chronotypes 27 and geographical position that determines the sleep timing 28,29 …”

Perspective: Daylight Saving Time—An Advocacy for a Balanced View and against Fanning Fear

“…Here, the higher light levels were in the evening, the less strong were the effects of a shift in the solar noon (expressed by longitude differences) on SJL and the occurrence of the body temperature nadir. Further support comes from a recent publication by Shochat et al [23]. Here, the authors conclude that "individual timing of sleep and activity in a modern environment with electrical lighting, largely conforms to clock time and actual light exposure (which is the combination of natural and electrical light exposure) rather than sun time indexed by the timing of SN (solar noon, A/N)".…”

“…Note that, although the findings do not imply causality and the timing of sleep also influences the timing of light exposure, any light exposure will impact the circadian pacemaker and thereby sleep timing [22,24]. Further support comes from a recent publication by Shochat et al [23]. Here, the authors conclude that "individual timing of sleep and activity in a modern environment with electrical lighting, largely conforms to clock time and actual light exposure (which is the combination of natural and electrical light exposure) rather than sun time indexed by the timing of SN (solar noon, A/N)".…”

Constant Light Exerted Detrimental Cardiovascular Effects Through Sympathetic Hyperactivity in Normal and Heart Failure Rats

“…The constant light exposure is not convincingly related to heart failure, while the light is reported to regulate cardiovascular function with the involvements of the circadian rhythm and cardiovascular hormones (e.g., melatonin and cortisol) (Furlan et al, 2000;Thosar et al, 2018;Gordijn, 2019;Hasegawa-Ohira et al, 2019;Lee et al, 2019;Petrowski et al, 2019). Natural sunlight exposure was considered to have a beneficial effect on heart function, while artificial light exposure looked like evil because of the adverse effect (Daugaard et al, 2019;May et al, 2019;Shochat et al, 2019). Considering the complexity of light, the biological effect of light was determined by a couple of factors like wavelength, duration, intensity and so forth.…”