Kids Who Got a Phone at 12 Had Double the Risk of Tying Worth to Weight by 14

A long running federal brain study enrolled 8,957 twelve year olds. By the time researchers checked back in two years later, 6,225 of them already owned a smartphone. By age 14, the phone owners were tying their self-worth to their weight at roughly double the rate of other kids. Those other kids hadn't had a phone at 12. They were binge eating 67 percent more often, and they reported any eating disorder symptom 49 percent more often.

The data came from the Adolescent Brain Cognitive Development Study, a National Institutes of Health project tracking kids at 21 US research sites. The paper ran in JAMA Network Open on September 25, 2026. Lead author Jason Nagata, a UCSF pediatrician, pulled smartphone ownership out as its own variable. Most research on this question has lumped phones into general screen time and stopped there. Worth noting: all 8,957 kids came from one long running cohort, not a one-off online poll. That continuity is part of why the numbers held up after statistical adjustment.

Nagata sees these patterns firsthand. He is an adolescent medicine physician at UCSF Benioff Children's Hospital. He described the mechanism to ABC7 News in San Francisco after the paper published.

“Having a smartphone can just put a world of appearance focused content in the young person's pocket.”

What changed between 12 and 14

The researchers adjusted for income, race, prior mental health diagnoses, and the eating disorder symptoms a child already had at 12. The risk ratios held anyway. Binge eating ran 1.67 times higher among phone owners, confidence interval 1.11 to 2.52. Self-worth tied to weight ran 2.03 times higher, interval 1.28 to 3.19. By 14, 24.2 percent of former phone owners reported at least one eating disorder symptom, against 15.5 percent of kids without an early phone.

What the study can't say

Nagata and his coauthors are explicit about the limits of the data. Reverse causation is possible. A kid already anxious about their body might get a phone sooner than other kids. Maybe a parent wants to monitor them more closely, or maybe the kid is just asking to fit in. The study tracked whether a child owned a phone, not what the child did with it. Nobody coded the actual apps, feeds, or hours spent.

“I think it's just really important for parents to stay involved with their children's digital lives.”

Nagata has spent nearly a decade on versions of this question. A study he led during the pandemic found that 12 and 13 year olds had roughly doubled their recreational screen time. It went from 3.8 hours a day to 7.7, and the jump tracked with more depression and anxiety. The new paper narrows that broad pattern down to one specific device and one specific set of symptoms.

A debate already underway

The timing matters. A University of South Florida survey of about 1,500 kids found that nearly two thirds already own a smartphone by age 10. That's two years before the age this study measured. More than 40 states now restrict phone use in K-12 schools. At least 26 have passed bell-to-bell bans that keep phones off for the entire day. The argument over whether kids should have phones at all is mostly settled by policy already. The argument over what's actually happening on the phone, measured the way Nagata just measured it, is only getting started.

For now, a parent deciding when to hand over the first phone gets an answer with a confidence interval attached. Built into that answer is a flat admission. Nobody has measured what happens in the two years between handing it over and the symptoms showing up.