First smartphone at 12 linked to less sleep and rising mental health symptoms

A study of nearly 3,500 US teenagers found that getting a smartphone between 12 and 13 was followed by more screen and social media use, less sleep and modest increases in anxiety, depression and attention symptoms.

For many families, the arrival of a first smartphone around the age of 12 can feel like a milestone of independence. New research suggests it may also mark a meaningful shift in adolescent well-being. A longitudinal analysis of nearly 3,500 US teenagers found that the move from not owning a smartphone to owning one was linked to more screen time, greater social media use, more media consumption in bed and less sleep, alongside a modest worsening in mental health symptoms over the following year.

The findings come from the Adolescent Brain Cognitive Development Study, a large national project that tracks child development over time. Researchers at the Children’s Hospital of Philadelphia and the University of Pennsylvania focused on 3,486 participants who did not have a smartphone at age 12. Of those, 1,546 had acquired one by age 13, while 1,940 remained without one. By comparing changes over the same period and accounting for each child’s starting point, the team aimed to isolate the effect of first ownership rather than differences that already existed between families.

The study is framed around the idea of the “digital exposome”, a term used to describe the full set of exposures that arise from interacting with digital technology. In that sense, a smartphone is more than a device: it can reshape routines, relationships and exposure to social feedback during a developmental stage when young people are especially sensitive to their environment. The researchers also adjusted their models for factors including age, sex, household income, parental education, race and ethnicity, pubertal stage, parental monitoring and ownership of other devices, such as tablets and laptops.

The mental health changes were small but measurable. Adolescents who acquired smartphones recorded slightly higher scores for internalising symptoms, which include anxiety and depression, as well as attention problems and overall symptom burden. By contrast, externalising symptoms, such as aggression and rule-breaking, did not show a significant change. The behavioural shifts were clearer: smartphone owners were more than three times as likely to have a social media account, spent more time on screens overall and were more likely to use social media, stream video or play games in bed before sleep, while school-night sleep duration fell.

Mediation analysis suggested that these changes may explain much of the relationship between smartphone ownership and later mental health symptoms. Social media account ownership accounted for the largest share of the association, followed by total screen time and bedtime media use. The researchers cautioned that the study cannot prove cause and effect, and that some influences, such as family dynamics or parenting style, may not have been fully captured. Even so, they argue that the first smartphone may be a useful point for parents and caregivers to set boundaries, especially around nighttime use, because the habits formed at that stage may matter for sleep and emotional health.