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. 2018 Nov;35(12):1748-1752.
doi: 10.1080/07420528.2018.1504784. Epub 2018 Aug 7.

Late Bedtimes Prevent Circadian Phase Advances to Morning Bright Light in Adolescents

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Late Bedtimes Prevent Circadian Phase Advances to Morning Bright Light in Adolescents

Stephanie J Crowley et al. Chronobiol Int. .
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Abstract

We examined phase shifts to bright morning light when sleep was restricted by delaying bedtimes. Adolescents (n = 6) had 10-h sleep/dark opportunities for 6 days. For the next 2 days, half were put to bed 4.5 h later and then allowed to sleep for 5.5 h (evening room light + sleep restriction). The others continued the 10-h sleep opportunities (sleep satiation). Then, sleep schedules were gradually shifted earlier and participants received bright light (90 min, ~6000 lux) after waking for 3 days. As expected, sleep satiation participants advanced (~2 h). Evening room light + sleep restriction participants did not shift or delayed by 2-4 h. Abbreviations: DLMO: dim light melatonin onset.

Keywords: Circadian rhythms; DLMO; adolescent; bright light; entrainment; evening light; phase response curve to light; phase shift; sleep; sleep deprivation.

Figures

Figure 1.
Figure 1.
Study protocol for a participant who usually woke up at 10:00 AM; fixed wake-up times on days 1–9 ranged from 07:00 to 11:00 AM. The study occurred during summer vacation. Black bars: sleep opportunity for all participants. Hashed bars: sleep satiation participants were in bed in the dark and given the opportunity to sleep; sleep restriction + evening light participants remained awake in room light (~140 lux). L’s: morning bright light (~6000 lux). White bars: circadian phase assessments to determine the dim light melatonin onset (DLMO), a marker of circadian phase.
Figure 2.
Figure 2.
Baseline and final salivary melatonin profiles. Open circles and dashed line: baseline melatonin profile. Closed circles and solid line: final melatonin profiles. Horizontal line at 4 pg/mL: threshold used to determine the DLMO. Arrows above the lines show the phase shift direction. Sleep satiation participants (P4-P6; left) phase advanced as expected from morning bright light (~6000 lux, three 30-min exposures) and the gradual advance of sleep/dark. Evening light (~140 lux) + sleep restriction participants (right) either did not shift (P2) or shifted in the wrong (delay) direction (P1 and P3) despite the same morning bright light and gradual advance of sleep/dark.

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