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Abstract Introduction Developmental shifts towards later sleep/circadian timing during adolescence are often at odds with early school start times, resulting in circadian misalignment and sleep restriction, as well as stark differences between sleep timing/duration on school nights versus weekends. While the sleep aspects of this mismatch have been well-characterized, limited objective data addresses within-person changes in circadian phase across the week. In a sample of high school students, this project aimed to (1) characterize within-person changes in circadian phase from school nights to weekend nights, and (2) examine whether later circadian phase relates to other sleep/circadian characteristics across the full week. Methods Sample included 115 high school students (mean age 17.3, 55.7% female, 88.7% White) reporting at least one “standard drink” of alcohol in their lifetime. Participants completed baseline self-report measures, wrist actigraphy for 8 days, and two overnight visits (Thursday and Sunday) for salivary melatonin sample collection. The Munich Chronotype Questionnaire assessed chronotype and social jetlag. Actigraphy measures included sleep onset latency (SOL), wake after sleep onset (WASO), total sleep time (TST), and midsleep timing. Circadian phase was calculated as the dim light melatonin onset (DLMO; 4 pg/ml threshold). Actigraphy and DLMO measures were separately calculated for school nights, weekends, and overall (mean). Linear regression was used to examine associations, covarying for sex, race, and SES. Results Circadian phase (DLMO) was systematically later on Sunday (mean 37+/-41 minutes later; d=0.68, p 0.00). Later school night DLMO was associated with longer SOL (b=0.05,p=0.002), shorter WASO (b=-0.03,p=0.018), and shorter TST (b=-0.18,p=0.001) on school nights, as well as later chronotype (b=-1.72,p 0.0001). Later weekend DLMO was associated with longer TST (b=0.22,p=0.042) on weekends. Later DLMO (school night, weekend, overall) was associated with larger weekday-weekend differences in actigraphic TST (p’s 0.001) and more social jetlag (p’s 0.03). Conclusion Circadian phase shows systematic within-person differences across school nights and weekends, broadly paralleling social jetlag based on sleep timing. While later circadian phase was associated with later chronotype, as well as more difficulty falling asleep and less sleep on school nights, this was specific to circadian phase assessed on school nights. Future studies should consider day-of-week of circadian assessments. Support (if any) R01AA025626(Hasler)
Hasler et al. (Sat,) studied this question.