Abstract
Background: Insufficient or low-quality sleep and poor mental healthaffect many adolescents worldwide. Although disrupted sleep has been related to mental illness at this age, existing research is predominantly cross-sectional, restricted to clinical populations, focuses on negative (i.e. illness) rather than positive (i.e. wellbeing) mental health, and has rarely examined bidirectionality. How screen time influences sleep health and the relationship between sleep and mental health is also uncertain, with existing research limited by self- reported measurement of screen time and cross-sectional designs.
Objectives: To: examine bidirectional relationships between mental health and sleep in adolescents (Chapter 4); assess the validity of daily sleep and screen time questionnaires against objective measures(accelerometery and video cameras) (Chapter5); examine whether evening screen use mediates the relationship between mental health and sleep using objective measurement (Chapter 6); and to examine whether time since screens are last used influences subsequent sleep that evening (Chapter 7).
Method: The Bedtime and Electronic Devices (BED) study was a seven-night repeated- measures within-person design to investigate the relationships between pre-bed screen use, sleep, and mental health among adolescents aged 11-14-years. Eighty-three participants were recruited between March and December 2021. Participants attended four study visits, wore Patrol Eyes DV7 video cameras on four non-consecutive nights to objectively measure screen use, wore one AX3 accelerometer on their wrist for 7 nights to measure sleep, and completed two brief daily questionnaires on sleep and screen use (morning) and mental health(evening). Video footage was coded by four trained coders using a validated coding schedule between 2022 and 2023, and inter- and intra-rater reliability were regularly assessed with weighted Cohen’s kappa (κ).
Results: Within-person analyses showed that better self-reported sleep quality and earlier bedtimes were associated with better health-related quality of life and mood the next day, while earlier wake times were also predictive of better mood. In addition, this study provided evidence of bidirectional relationships between sleep qualityand mental health,indicating that better mentalhealth that day predicted bettersleep quality that evening, and better sleep quality that night predicted better mental health the following day. Validation analysesrevealed that
while adolescents were reasonably accurateat estimating their bedtime and shuteye time (when they first attempt sleep), estimations of sleep duration were poor. In terms of screen time, adolescents were good at recalling whether they had used screens the night before or not, but were poor at quantifying this use, particularly for multitasking (using multiple devices simultaneously). Bettermental health that day predictedless screen use in bed that eveningand those who were in a happier mood during the day had a better quality of sleep that night. Mediation analysis revealed that screen use in bed mediated the relationship between mood and sleep. Finally, time since screens were last used had almost no impact on sleep health.
Conclusion: This thesisprovides support for a bidirectional relationship between mentalhealth and sleep among adolescents, with mediation analysisindicating that eveningscreen use might partly explain this relationship. However, caution must also be expressed regarding the ability of adolescents to accurately estimate their screen and sleep times, which limits the ability to draw firm conclusions from self-reported data. Additional concerns were highlighted by analyses showing that when screen time and sleep were measured objectively, time since screenswere last used did not influence any measure of sleep healthexamined. Such data cast doubt on current sleep guidelines which recommend adolescents to stop using screens in the hour or two before bed.