A new study of 2,500 teenagers suggests that frequent use of digital media can lead to higher risk of developing ADHD-related symptoms

The more teens use social-media networking sites, video games and streaming services, the higher their risk of developing symptoms of attention-deficit hyperactivity disorder, or ADHD, a new study found.

The study, published Tuesday in the Journal of the American Medical Association, tracked 2,500 teens over two years and monitored their usage and symptoms.

It doesn’t prove a causal link. The study also didn’t rule out other possible causes such as lack of sleep, family stress at home or a family history of the disorder. But it was the first longitudinal study to follow so many teens over a two-year period, according to experts, going straight to an issue that pits parents and teachers against the tech industry in a battle for children’s attention.

“I don’t think it’s reason for panic. But I’m a clinician who sees kids with ADHD all the time, and I don’t want to see an increase,” says Jenny Radesky, a University of Michigan assistant professor of pediatrics, who specializes in developmental and behavioral health.

“Executive function and flexible problem solving—all that matters for long-term success,” she said. “Even if it’s a small increase in ADHD, I think that’s important.” Such skills are often affected by ADHD. Dr. Radesky, who wrote a JAMA editorial about the new study, wasn’t involved in the work.

Use of technology could be one of several environmental factors related to ADHD. Research suggest that smoking and drug use during pregnancy and lead exposure during childhood may also increase the risk of developing the disorder, according to the U.S. National Institutes of Health. Genetics frequently come into play.

Many of the major tech companies this year have said they are mindful of the risks of too much screen time, and are launching various measures to curb the use by those who might be susceptible to overload. But it isn’t yet clear whether those nascent efforts are having an effect.

The new study is an important early step toward understanding the impact on the developing brain of media enabled by the internet, apps and mobile devices, and shows that more research is needed, scientists said.

For the study, students answered questionnaires every six months about their media diet—including checking social media, browsing videos, video chatting and online shopping—and frequency of use, plus assessments of ADHD-related symptoms.

If students reported experiencing six or more symptoms on these self-assessments, researchers considered them positive for ADHD symptoms. Because the researchers wanted to assess whether media use was associated with new symptoms, the study excluded teens who exceeded that threshold when the study began, said Adam M. Leventhal, the study’s lead author and the director of the University of Southern California’s Health, Emotion and Addiction Laboratory at USC’s Keck School of Medicine.

Teens didn’t get a formal diagnosis for the study; “a clinical interview from a mental-health practitioner is needed to confirm a diagnosis for any psychological disorder, including ADHD,” said Dr. Leventhal

The roughly 500 teens who didn’t report using digital media multiple times each day had a 4.6% rate of having ADHD symptoms, such as difficulty completing tasks or remaining still. Among the roughly 50 who reported daily use of all 14 different types of digital media included in the study, the rate was 10.5%. Altogether, roughly 550 experienced ADHD symptoms in the six-month intervals between surveys, according to the study.

Common Sense Media, a nonprofit that promotes safe media use for children, sponsored a survey of 620 teens in May 2016, which found 78% said they check their mobile devices at least hourly.

Previous research has shown that incessant distractions and stimuli from tech use might diminish children’s ability to concentrate. Scientists worry this could also harm kids’ ability develop skills like patience and delayed gratification. This study is notable because it didn’t focus on the exact amount of daily or weekly screen time, which has become less meaningful as teens toggle between apps on phones that often stay on much of the day. Rather, the study asked teens what digital media they use and how often, which Dr. Radesky believes yielded more accurate information.

“We’re always looking for the quick and dirty answer for why there’s so much depression and ADHD these days,” said Stephen P. Hinshaw, a University of California, San Francisco professor of psychiatry who wasn’t involved in the study. “But if we say ‘Oh my god! Social media use leads to ADHD,’ that’s misleading.”