Abstract
Many adolescents fall asleep too late to get enough sleep (8–10 h) on school nights. Morning bright light advances circadian rhythms and could help adolescents fall asleep earlier. Morning bright light treatment before school, however, is difficult to fit into their morning schedule; weekends are more feasible. We examined phase advances in response to morning light treatment delivered over one weekend. Thirty-seven adolescents (16 males; 14.7–18.0 years) who reported short school-night sleep (≤7 h) and late bedtimes (school-nights ≥23:00; weekend/non-school nights ≥24:00) slept as usual at home for ∼2 weeks (“baseline”) and then kept a fixed sleep schedule (baseline school-night bed and wake-up times ±30 min) for ∼1 week before living in the lab for one weekend. Sleep behavior was measured with wrist actigraphy and sleep diary. On Saturday morning, we woke each participant 1 h after his/her midpoint of baseline weekend/non-school night sleep and 1 h earlier on Sunday. They remained in dim room light (∼20 lux) or received 1.5 or 2.5 h of intermittent morning bright light (∼6000 lux) on both mornings. The dim light melatonin onset (DLMO), a phase marker of the circadian timing system, was measured on Friday and Sunday evenings to compute the weekend circadian phase shift. The dim room light and 1.5-h bright light groups advanced the same amount (0.6 ± 0.4 and 0.6 ± 0.5 h). The 2.5-h bright light group advanced 1.0 ± 0.4 h, which was significantly more than the other groups. These data suggest that it is possible to phase advance the circadian clock of adolescents who have late bedtimes and short school-night sleep in one weekend using light that begins shortly after their sleep midpoint.
Highlights
Sleep regulatory mechanisms undergo developmental changes that shift alertness later into the evening and night for older post-pubertal adolescents
The circadian timing system is later (Carskadon et al, 1997, 2004; Crowley et al, 2014) and homeostatic sleep pressure accumulates at a slower rate during waking in more mature adolescents compared to their prepubertal peers (Jenni et al, 2005; Taylor et al, 2005)
Three participants discontinued the study during baseline and one participant assigned to the room light group decided to discontinue the study during the laboratory weekend
Summary
Sleep regulatory mechanisms undergo developmental changes that shift alertness later into the evening and night for older post-pubertal adolescents. The average school-day wake time for a high schooler in the United States is between 6 and 6:30 am (Wolfson and Carskadon, 1998; Crowley et al, 2007, 2014; Short et al, 2017), and many other countries report school-day wake times of 07:00 or earlier (Gradisar et al, 2011b; Short et al, 2017) This pattern of early school-day wake times and late sleep onset puts older adolescents at an increased risk for getting less than the recommended 8–10 h of sleep per night (Hirshkowitz et al, 2015; Paruthi et al, 2016) on school nights, and less than the 9–9.25 h per night that is required for cognitive function/attention (Short et al, 2018) and for emotion regulation (Fuligni et al, 2017)
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