This cohort study followed 1,959 adolescents (mean age ~12.7 years at baseline, ~14.0 years at follow-up) from the ABCD Study to examine whether smartphone acquisition around age 13 and daily smartphone use time were associated with depression, obesity, and insufficient sleep at age 14, adjusting for baseline health status, socioeconomic factors, and use of other devices.
Smartphone acquisition alone was not significantly linked to depression (OR 1.45; 95% CI 0.98–2.14) or obesity (OR 1.02; 95% CI 0.71–1.46), but was associated with insufficient sleep (OR 1.29; 95% CI 1.03–1.62). Among those with a smartphone, greater daily use time was associated with all three outcomes: depression (OR 1.22), obesity (OR 1.34), and insufficient sleep (OR 1.28). Keeping smartphones out of the bedroom at bedtime was linked to lower odds of insufficient sleep (OR 0.64; 95% CI 0.47–0.87).
- Only adolescents without a smartphone at age 13 were eligible, limiting generalizability to those who acquired phones earlier. - Smartphone use duration was self-reported, introducing recall bias. - The sample was predominantly White (84.8%), limiting ethnic diversity and broader generalizability.
Counsel families that simply getting a smartphone at 13 is less important than how much it's used — limiting screen time and banning phones from bedrooms at night are concrete steps to reduce sleep problems, depression risk, and obesity in teens. Policies focused solely on delaying acquisition age may be insufficient without accompanying guidance on usage habits.
