Adolescent smartphone use, sleep, and physical activity: daily associations between sensor-based measures in the...

Potential health consequences of adolescent smartphone use are a growing public concern. Improving upon existing, largely self-report-based research, this study investigated relationships between adolescent smartphone use, sleep, and physical activity using passive sensor measures.

Over three weeks, 791 Adolescent Brain Cognitive Development (ABCD) Study participants (M_age=14.12, 53 % female) provided smartphone application and keyboard use data via the Effortless Assessment Research System (EARS) application, and sleep and physical activity data via Fitbit device.

Mixed-effects models found that daytime/evening application use (6:00AM-7:59PM) predicted reduced exercise, more time sedentary, and fewer daily steps (Standardized β=-0.21-0.07, P<.001). Late-evening use (8:00PM-9:59PM) modestly predicted increased sedentary time and reduced steps (Standardized β=-0.05-0.02, P<.001). Late-night use (10:00PM-5:59AM) predicted reduced sleep, delayed sleep onset, delayed waking, increased sedentary time, and fewer daily steps (Standardized β=-0.16-0.27, P<.001). After disaggregating within and between-person smartphone use, within-person relationships remained significant, with associations of similar magnitude to the initial analyses (daytime/evening use: standardized ꞵ=-0.22-0.07, P<.001; late-evening use: standardized ꞵ=-0.05-0.02, P<.001; late-night use: standardized ꞵ=-0.16-0.24, P≤.002), indicating daily-level relationships unattributable to between-subject differences. Examining smartphone use effects by hour relative to sleep onset indicated that only use recorded after initial sleep onset significantly predicted sleep, while use recorded 3-12 hours before sleep onset significantly predicted step counts.

Using passive sensor data, we found significant associations between adolescent smartphone use, physical activity, and sleep which differed by time of day and remained significant within subjects. Experimental replication is recommended to strengthen tentative causal claims.