Which came first; a teenager nose-deep in a smartphone or the ADHD diagnosis?

It’s the modern-day version of the chicken and the egg — and it’s the reason researchers at the University of Southern California studied over 2,000 teenagers for two years.

Adam Leventhal, USC professor and study author says the data suggests too much online time does indeed lead to problems with hyperactivity and impulsivity. They found a link between a hefty digital media diet and a later ADHD diagnosis in the teens.

Previous research was conducted before the advent of smartphones. Leventhal says media teens are ingesting has changed.

"The speed and the number of different entertainment options and unlimited access during the day via phone or your tablet," said Leventhal.

So when your teen wants to binge an entire season of a Netflix show in one day, it should go without saying that patience and delayed gratification are not skills they’ll be downloading.