JOHN YANG: A new study has found a link between preteens use of social media and future depression.

The study was conducted by researchers at the University of California, San Francisco and published this week in the American Medical Journal's association journal JAMA.

The study said more time spent on social media may contribute to increased depressive symptoms over time.

Ali Rogin spoke with the lead researcher, Dr. Jason Nagata.

ALI ROGIN: Dr. Nagata, thank you so much for joining us.

Social media children, lots of questions, few answers.

What did your study find?

DR. JASON NAGATA, University of California, San Francisco: We followed 12,000 preteens over three years and we actually found big rises in social media use.

So during that period, social media on average increased from seven minutes a day to over 70 minutes a day.

So a tenfold increase.

And in our analysis, we actually found that rises in social media from year to year among these 9 then 10 then 11-year olds were actually associated with future depressive symptoms in the following year.

So I think there's a big kind of unknown in the field right now.

Chicken or the egg?

Does social media precede depression or is it maybe just reflection of underlying symptoms?

And I think that our study does show a little bit more stronger evidence that social media is a risk factor for future depression in these kids.

ALI ROGIN: So what you're saying is that you found the correlation here to be with social media use leading to more depressive symptoms, not the other way around.

You're saying that depression doesn't necessarily indicate use of social media?

JASON NAGATA: Yes.

In our study, were able to follow these same 12,000 kids year to year.

So were able to look at both their depression and their social media use every single year.

And so we could look at patterns in their use.

And we found that those kids who had big spikes in their social media use from year to year then subsequently had bigger spikes in their depression.

But those kids who started off with increases in depression didn't necessarily use social media more.

So it is indicating a little bit more of directionality that social media could be a risk factor for future depression.

ALI ROGIN: And talk to us about the size and the scope of this study.

This sounds massive.

How did you track this many children and has that been done before?

JASON NAGATA: So, yeah, the data comes from the Adolescent Brain Cognitive Development Study.

It is a national study that follows these 12,000 kids from over 21 different states, study sites across the U.S. and it's funded by the National Institutes of Health and is I think one of the largest studies on child development and social media and brain health ever.

ALI ROGIN: You are a physician, I know you're also a parent.

And I wonder, seeing these results, what does it make you hope policymakers consider when thinking about social media's impact on children?

JASON NAGATA: I think one really important thing for policymakers to know is that technically the minimum age requirement for social media is 13 years.

But this study essentially represented underage use of social media and we found that even among 11 to 12 year olds, over two-thirds had social media accounts and on average they had three or more different accounts.

So these are all kids who had to put in fake dates of birth in order to get access to these sites.

And I think it's just a reminder that there's not really robust age verification.

So any kid, no matter their age, as long as they can put in a fake date of birth currently is able to very easily access these sites.

And many of the kids did report that they had secret accounts that their parents didn't know about.

So I think one thing for policymakers to really understand is that the landscape right now is very easy for kids to get on and there aren't very strong securities for privacy and protection for kids.

ALI ROGIN: That's such a fascinating ancillary piece of information that you found in looking at this data.

I do want to ask though, what is your advice for parents with the understanding that this data brings us to.

JASON NAGATA: Yeah, we actually looked at parent actions for rules and monitoring in the study and we actually found that the biggest predictors of kids screen use was actually their parents screen use.

And as a new parent I think it's really important to practice what you preach.

So if you're going to tell your kids to put down their phones to important that you role model good behaviors otherwise your kids aren't going to follow the rules.

The other two times that it might be really high yield to limit screen use is bedtime to try to promote good sleep and also around meal time to prevent overeating because we know kids tend to overeat while they're distracted in front of screens and also encourage in person connections and conversations around the dinner table.

ALI ROGIN: Limiting social media around our kids.

Something I think most parents, including myself, should, should heed.

Dr. Jason Nagata with the University of California, San Francisco.

Thank you so much for joining us.

JASON NAGATA: Thanks so much for.