Screen time effects on adolescent mental health

Introduction: Depression and anxiety are the most common causes of illness in Europe, especially among young people, and suicide is the leading cause of death among adolescents in Sweden. The use of digital media is often discussed in relation to mental health. Time recommendations, bans, legislation, and media use guidelines are frequently published-often without clear evidence of their effects or mechanisms of action. This thesis aims to improve our understanding of this phenomenon.

Aim: Through three studies (I, II, III), this thesis explores the main psychological health mechanisms involved in how leisure screen time may contribute to mental health issues-or simply co-occur with them. It aims to establish a theoretically grounded, empirically supported, and scientifically replicable framework and model for understanding how screen time affects mental health.

Methods: Longitudinal three-wave psychometric health data were collected over six years in conjunction with two school-cluster randomized trials on psychoeducation and suicide prevention, always administered in classroom settings. Intervention effects were held constant or nullified. Three statistical analyses of screen-health associations were conducted using adolescent health data (N = 4810 from 55 Swedish schools; N = 1544 from 30 schools in seven European countries).

Analyses: The primary health outcome was subclinical depression (BDI-II scores), which correlated with anxiety, and stress (DASS-42). All main statistical tests were longitudinal (3-12 months). Study I used hierarchical linear regression of change scores to examine screen activities and their consequences. Study II applied GEE gamma regression to examine moderating effects of coping styles and structural regression to assess their mediating pathways. Study III used preregistered, theory-driven multigroup structural equation modelling to analyze multiple mediation and simultaneous screen-sleep displacements.

Results: Screen time consistently had a negative impact on various sleep patterns and reduced cognitive coping styles. It was associated with small but adverse health outcomes for the average adolescent. Girls had twice the depression levels of boys and appeared more sensitive to screen-related sleep loss. Long screen times negatively affected Problem-Focused Engagement (PFE) coping, including cognitive restructuring, but not Socio-Emotional coping (EFE) (data collected before the COVID-19 outbreak). Notably, moodiness when screens were inaccessible-i.e., difficulty coping without screens-was the strongest predictor of depression in the first European study.

Discussion: The three studies showed that, regardless of gender, longer screen time was associated with sleep loss and/or reduced ability to cope with stress. Independent research confirms that sleep loss further reduces the tendency to use cognitive engagement coping. While causality could not be established, the correct temporal order was identified in the two latter studies, which replicated the initial exploratory findings. The final framework is termed the "Screen Time Displacement Theory of Mental Health" (though not so important). Sleep problems often underlie depression-especially among girls in this sample- where sleep facets (quality, duration, chronotype) mediated 38-57% of the depressive effect over 12 months. Problem-focused coping both mediated and moderated depression in both genders over 12 months (the screen-coping interaction effect equaled maximum +3.4 BDI-II points; p < 0.01). Effective coping styles and consistently sufficient sleep are essential components of psychological and physiological resilience to depressive states, yet most adolescents do not meet conventional sleep or screen time recommendations. This thesis demonstrates the effects of screen time on mental health resilience in the general adolescent population (at least within Generation Z), as opposed to clinical samples. Various implications for public health are discussed.

List of scientific papers

I. Hökby S, Hadlaczky G ... Carli V. Are Mental Health Effects of Internet Use Attributable to the Web-Based Content or Perceived Consequences of Usage? A Longitudinal Study of European Adolescents? JMIR Ment Health. 2016. 13;3(3):e31. https://doi.org/10.2196/mental.5925

II. Hökby S, Westerlund J, Alvarsson J, Carli V, Hadlaczky G. Longitudinal Effects of Screen Time on Depressive Symptoms among Swedish Adolescents: The Moderating and Mediating Role of Coping Engagement Behavior. IJERPH. 2023;20(4):37. https://doi.org/10.3390/ijerph20043771

III. Hökby S., et al. Adolescents' screen time displaces multiple sleep pathways and elevates depressive symptoms over twelve months. PLOS Glob Public Health. 2025, 2;5(4):e0004262. https://doi.org/10.1371/journal.pgph.0004262