Association of evening smartphone use with cardiac autonomic nervous activity after awakening in adolescents living in high school dormitories
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Smartphones are prevalently used among adolescents; however, nighttime exposure to blue-enriched light, through electric devices, is known to induce delays of the circadian rhythm phases and poor morning somatic conditions. We therefore investigated whether evening smartphone use may affect sleep-wake cycle and cardiac autonomic nervous system (ANS) activity after awaking in dormitory students.
The participants were high school students, living under dormitory rules regarding the curfew, study, meals, lights-out, and wake-up times. The students were forbidden from the use of both television and personal computer in their private rooms, and only the use of a smartphone was permitted. According to prior assessment of smartphone use, we chose age-, sex-, exercise time-matched long (n = 22, >120 min) and short (n = 14, ≤60 min) groups and compared sleep-wake cycle and physiological parameters, such as cardiac ANS activity, blood pressure, and intra-aural temperature. All measurements were performed during 6:30 to 7:00 a.m. in the dormitories.
Compared with the short group, the long group showed a significantly lower cardiac ANS activity (2727 ± 308 vs. 4455 ± 667 ms2, p = 0.030) with a tendency toward a high heart rate, in addition to later bedtimes during weekdays and more delayed wake-up times over the weekend. Blood pressure and intra-aural temperature did not differ between the groups.
In this population, evening smartphone use may be associated with altered sleep-wake cycle and a diminished cardiac ANS activity after awakening could be affecting daytime activities.
KeywordsLight-emitting electronic devices School dormitory Sleep-wake cycle Autonomic nervous system
We are grateful to all participants, their parents, high school teachers, and housemothers and fathers of the dormitories for their cooperation. We also wish to express our appreciation to Dr. Kaneyoshi Ishihara, in Notre Dame Seishin University, who gave us the permission to use the Japanese version of MEQ. This work was supported by JSPS KAKENHI Grant Numbers 24500988 and 15H02901.
Compliance with ethical standards
Conflicts of interest
The authors declare that they have no conflicts of interest.
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