Smartphone acquisition as an inflection point in early adolescence digital exposome: relevance to mental health.

Abstract

Objective: Acquisition of the first smartphone represents a major developmental transition. However, evidence on its effects on adolescent health and behavior remains limited. We assessed associations between first smartphone acquisition around age 12 and changes in mental health, environmental and lifestyle (exposomic) factors, and examined potential pathways underlying these associations.

Methods: We analyzed longitudinal data from 3,486 participants in the U.S. Adolescent Brain Cognitive Development (ABCD) Study who did not have a smartphone by age 12 (2-year assessment wave). We tested the association between smartphone acquisition (exposure) between age 12 to 13 (the 2- and 3-year assessments) and age 13 self-reported mental health (Brief Problem Monitor [BPM]) and exposomic outcomes including digital (screen time, social media, gaming, streaming, cyberbullying) and offline (sleep duration, school performance, exercise, bullying and reading) measures. Mixed-effects regression models accounted for sociodemographic, family, and developmental covariates. To reduce confounding, models additionally adjusted for pre-exposure measures of each outcome assessed at age 12, prior to smartphone acquisition. Mediation models examined indirect effects of smartphone acquisition on mental health through total screen time, social media account ownership, and bedtime media use.

Results: Compared with youth who remained smartphone-free at age 13 (n = 1,940), smartphone acquisition (n = 1,546) was associated with worse BPM internalizing, attention, and total scores (all p's ≤ 0.003), more screen time, greater odds of having a social media account, less sleep, and more frequent bedtime use of social media, video games, and streaming (all p's < 0.001). Smartphone acquisition was not associated with differences in externalizing symptoms, academic performance, exercise, or bullying/cyberbullying (all p's > 0.05). Mediation analyses suggested indirect associations between smartphone acquisition and mental health through total screen time, social media account ownership, and bedtime media use (all indirect effects p ≤ 0.002); collectively, these factors accounted for most of the association, with social media use contributing the largest indirect effect.

Conclusion: Smartphone acquisition is associated with several environmental and lifestyle changes in the following year, particularly around bedtime. These changes may represent mechanisms linking smartphone acquisition to mental health symptoms. Findings provide insight into potential behavioral pathways associated with smartphone acquisition and adolescent mental health and may inform future intervention studies.