NEW YORK (CBSNewYork)–Attention-deficit/hyperactivity disorder (ADHD) is on the rise and now a new study suggests that might be due to excessive smartphone use.

“I’d say half the day, probably, I’m on my phone,” one teen said.

It’s no surprise many teens admit to spending too much time on their phones.

“Usually when I’m in class I’m always on my phone,” another teen said.

A new study suggests that the more teens check social media, stream video, text or simply use their phones–the more likely they are to develop symptoms of ADHD.

“In a sample of more than 2,500 Los Angeles area teenagers, and we found indeed, yeah there was a statistically significant link,” said University of Southern California study author Dr. Adam Leventhal.

ADHD symptoms include inattention, hyperactivity and restlessness that is more frequent than normal.

At its start, the 10th graders in the study had none of those symptoms.

For two years the teens kept track of their digital use and those ADHD behaviors.

The results, just published in the Journal of the American Medical Association, found a “statistically significant but modest association” between the two.

45 percent of the study adolescents admitted to being online, “almost constantly.”

The researchers say it’s the “always-on” nature of mobile devices and their frequent notifications, constantly drawing teens’ attention that may be behind the increase in ADHD symptoms.

Dr. Leventhal says parents can ease the problem by setting an example.

“Don’t use digital media so much in front of them. A lot of us do it and we don’t realize that maybe at the dinner table or other situations–we’re on our device!” said Leventhal.

Total screen time, TV and video games for example, did not correlate with increased ADHD because they don’t draw and demand attention the way phones do.

Still this is an association not a cause and effect and the increase was just 10 percent.