Nobody who lives with a teenager or sees teenagers in action could be surprised to hear that they are heavy users of tech — staring constantly at smartphones and other devices as they text one another, post photos, stream video and play games.

But are they driven to distraction by their tech addiction? Does the constant checking for messages on social media lead to ADHD? Research published Tuesday suggests that it might.

If heavy tech use is linked with ADHD, the effect was “modest,” according to the team at the University of Southern California.

“More frequent use of digital media may be associated with development of ADHD symptoms,” Adam Leventhal of USC’s Health, Emotion and Addiction Laboratory and colleagues wrote in their report, published in the Journal of the American Medical Association.

“Among adolescents followed up over two years, there was a statistically significant but modest association between higher frequency of digital media use and subsequent symptoms of ADHD.”

What’s not clear is whether the tech use causes ADHD or if perhaps kids who develop ADHD are more prone to heavy use of social media, streaming video and games.

Attention deficit/hyperactivity disorder, or ADHD, is common. The Centers for Disease Control and Prevention estimates that 6.1 million children have been diagnosed with ADHD, or about 9.4 percent of kids and teens.

And digital tech use is also common. The group Common Sense Media has found that teenagers spend an average of nine hours a day looking at screens, including phones and television. (They also found parents spend about the same amount of time looking at screens, by the way.)

Leventhal’s team looked at surveys of nearly 2,600 10th graders — aged 15 and 16 — taking part in a larger study of happiness across the Los Angeles area.

None had symptoms of ADHD at the start.

They were asked how often they used digital media, and then followed for two years to see if more developed ADHD.

Kids used digital tech a lot. More than half said they frequently checked social media sites and texted. More than 40 percent said they looked at pictures or streamed videos frequently and 38 percent streamed or downloaded music frequently.

Those most addicted to social media sites were 53 percent more likely to develop ADHD symptoms, the team reported. Frequent texters were 21 percent more likely than infrequent texters to show ADHD symptoms. Fans of pictures and streaming video were 45 percent more likely to report ADHD symptoms.

Only 8.8 percent of the students said they frequently used video chatting, but they were more than twice as likely to have ADHD symptoms, the survey found.

“It is worth noting that over 80 percent of students reported high frequency use of digital media, and the vast majority of these students do not have elevated ADHD symptoms,” said Dr. Jessica Agnew-Blais, who researches psychology and neuroscience at King’s College London and who was not involved in the study.

The team only found 495 students who said they did not use media heavily. About 4.6 percent of them developed ADHD symptoms over the next two years. Only 114 of the students reported they used tech for seven different activities frequently, but 9.5 percent of them developed ADHD symptoms.

"This study raises concern whether the proliferation of high-performance digital media technologies may be putting a new generation of youth at risk for ADHD," Leventhal said in a statement.

It is not clear how well the group studied represents U.S. teens as a whole.

It was a select group of teens pulled from schools where many of the students expressed interest in taking part in a larger study of happiness and health and whose parents gave permission. Half were girls, nearly half were Hispanic, 15 percent were African American and 15 percent were white.

And the study relied on self-reported symptoms. That raises questions about the accuracy of the findings.

“The study doesn’t measure either digital media use or ADHD directly. For both the study relies on survey responses provided by the student in question,” noted Andy Przybylski, of the Oxford Internet Institute at Britain’s University of Oxford, who was not involved in the study.