Smartphone owners at 12 had a 36% higher chance of reporting eating-disorder symptoms in a US cohort

The 36% is a relative figure ^[1]. ScienceAlert's account of the paper gives one absolute rate: by 14, nearly a quarter of children who had owned a phone since 12 reported at least one eating-disorder symptom ^[5]. The account does not give the matching rate for non-owners, or say what the ratios were adjusted for. If the 49% gap at 14 ^[7] were a plain ratio of raw rates, non-owners would sit at roughly 16 to 17%, about eight percentage points below owners ^[19]. An adjusted ratio would not convert so neatly, so that figure is a rough guide.

Then the control. Nearly 70% of the 12-year-olds owned a smartphone ^[3], so the comparison group is the minority, roughly 2,700 of the nearly 9,000 children ^[18]. Families who hold off on a phone at 12 are making a choice. Whatever drives that choice may also shape how their children eat and think about their bodies. ScienceAlert notes that the results cannot prove smartphones cause the symptoms ^[9].

The design has a real strength. The data come from an ongoing longitudinal study of US adolescents ^[13], so the same children could be followed from 12 to 14. But ownership at 12 was already linked to a range of symptoms at that age, and some of those associations were still present two years later ^[14]. Because the gap existed at the start, the age-14 numbers cannot cleanly separate two years of phone use from a difference the groups already had. The other headline figures, a 61% higher prevalence of binge-eating symptoms among 12-year-old owners ^[2] and a 103% higher likelihood of tying self-worth to weight ^[6], come from the same owner versus non-owner comparison.

The outcome is a reported symptom, not a diagnosis ^[8]. By early adulthood, eating disorders affect between 5.5 and 18% of young women and up to 2.4% of young men ^[15]. One reported symptom in a quarter of 14-year-old owners is a much lower bar than that. The exposure is coarse as well: owning a phone. The authors' proposed path runs through what the phone gives access to. "Owning a personal smartphone during early adolescence may be particularly consequential, given its potential to increase unsupervised and individualized exposure to digital environments during a sensitive developmental period," they wrote ^[16]. Other research has linked some phone uses to benefits, such as lower depression among teens who text more ^[17].

In my view the screening suggestion is the part of the advice the data support best. The authors, led by UCSF pediatrician Jason Nagata and publishing in JAMA Network Open ^[4], suggest clinicians ask about smartphone ownership and social media use when assessing eating-disorder risk ^[10]. The question costs a clinician little. It flags a group with higher symptom rates whether or not the phone is the cause. "Eating disorders are serious, potentially life-threatening conditions that are nonetheless often preventable and responsive to early interventions," the authors wrote ^[11].

Delaying phones is a harder call. The authors argue platform rules will not do it for parents: "While major social media platforms enforce a minimum age of 13 years, this threshold can be easily circumvented, raising concerns about the feasibility of age-based protections," they wrote ^[12]. The reported comparison is fixed at age 12 ^[1]. It does not test what waiting until 13 or 14 would change.