Many students self-report that they are “night owls,” which can result from neurodevelopmental
delays in the circadian timing system. However, whether an individual considers themselves to be
an evening-type versus a morning-type (self-reported chronotype) may also be influenced by
academic demands (e.g. class start times, course load) and behavioral habits (e.g. bedtime social
media use, late caffeine consumption, daytime napping). If so, then chronotype should be malleable.
We surveyed 858 undergraduate students enrolled in demanding science courses at up to
three time points. The survey assessed morning/evening chronotype, global sleep quality, academics,
and behavioral habits. Evening and morning-type students showed similar demographics,
stress levels, and academic demands. At baseline measurements, relative to morning-types,
evening-types showed significantly worse sleep quality and duration as well as 22% greater
bedtime social media usage, 27% greater daytime napping duration, and 46% greater likelihood
of consuming caffeine after 5pm. These behavioral habits partially mediated the effects of selfreported
chronotype on sleep quality/duration, even after controlling for demographic factors.
Interestingly, 54 students reported switching from being at least moderate evening-types at
baseline to being at least moderate morning-types later in the semester and 56 students showed
the reverse pattern (6.3% of students switched from “definitely” one chronotype to the other
chronotype). Evening-to-morning “chrono-switchers” consumed less caffeine after 5pm and
showed significantly better sleep quantity/quality at the later timepoint. Thus, some students
may consider themselves to be night owls in part because they consume caffeine later, take more
daytime naps, or use more social media at bedtime. Experimental work is needed to determine
whether nudging night owls to behave like morning larks results in better sleep health or academic
achievement.
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Low-intensity scheduled morning exercise for adolescents with a late chronotype: a novel treatment to advance circadian phase?
During adolescence, an interplay between biological and environmental factors leads to constrained sleep duration and timing. The high prevalence of sleep deprivation during this developmental period is a public health concern, given the value of restorative sleep for mental, emotional, and physical health. One of the primary contributing factors is the normative delay of the circadian rhythm. Therefore, the present study aimed to evaluate the effect of a gradually advanced morning exercise schedule (30 min shift each day) completed for 45 min on 5 consecutive mornings, on the circadian phase and daytime functioning of adolescents with a late chronotype, compared with a sedentary control group.
A total of 18 physically inactive male adolescents aged 15–18 years spent 6 nights at the sleep laboratory. The morning procedure included either 45 min walking on a treadmill or sedentary activities in dim light. Saliva dim light melatonin onset, evening sleepiness, and daytime functioning were assessed during the first and last night of laboratory attendance.
The morning exercise group had a significantly advanced (earlier) circadian phase (27.5 min ± 32.0), while sedentary activity resulted in a phase delay (−34.3 min ± 53.2). Morning exercise also led to higher evening sleepiness in the earlier hours of the night, but not at bedtime. Mood measures improved slightly in both study conditions.
These findings highlight the phase-advancing effect of low-intensity morning exercise among this population. Future studies are needed to test the transference of these laboratory findings to adolescents’ real life.
- NSF-PAR ID:
- 10369366
- Publisher / Repository:
- Oxford University Press
- Date Published:
- Journal Name:
- SLEEP Advances
- Volume:
- 3
- Issue:
- 1
- ISSN:
- 2632-5012
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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