Objectives: Given concerns regarding health implications of adolescent smartphone use, we tested associations of smartphone ownership and age of smartphone acquisition with depression, obesity, and insufficient sleep in early adolescence. We hypothesized that smartphone ownership, especially at a younger age, would be associated with worse health outcomes.

Methods: The sample included 10 588 participants from the Adolescent Brain Cognitive Development Study. Mixed-effects logistic regression models tested associations of smartphone ownership and age of first smartphone acquisition, reported by caregivers, with depression, obesity, and insufficient sleep at age 12 years. Among participants who did not own smartphones at age 12 years, we tested associations of recent acquisition of smartphones with outcomes in the subsequent year. Models were adjusted for demographic and socioeconomic variables, ownership of other devices, pubertal development, and parental monitoring.

Results: At age 12 years, compared with not owning a smartphone (n = 3849), smartphone ownership (n = 6739) was associated with higher risk for depression (odds ratio [OR] 1.31, 95% CI: 1.05-1.63), obesity (OR 1.40, 95% CI: 1.20-1.63), and insufficient sleep (OR 1.62, 95% CI: 1.46-1.79). Younger age of smartphone acquisition was associated with obesity and insufficient sleep (for each earlier year of acquisition, OR 1.09, 95% CI: 1.02-1.16, and OR 1.08, 95% CI: 1.02-1.12, respectively). At age 13 years, among 3486 youth who did not own a smartphone at age 12 years, those who had acquired a smartphone in the past year (n = 1546) had greater odds of reporting clinical-level psychopathology (OR 1.57, 95% CI: 1.12-2.20) and insufficient sleep (OR 1.50, 95% CI: 1.26-1.77) compared with those who had not (n = 1940) after controlling for baseline mental health and sleep. Results were consistent across several sensitivity analyses.

Conclusions: Smartphone ownership was associated with depression, obesity, and insufficient sleep in early adolescence. Findings provide critical and timely insights that should inform caregivers regarding adolescent smartphone use and, ideally, the development of public policy that protects youth.