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Remember the look on your teen’s face when he or she opened that Christmas gift, and found the latest-model iPhone? Oh, the joy of it. Who wouldn’t be thrilled, seeing as how that phone may have cost more than your first car.

But, like many things in life, that euphoria may not last. A new study from experts at San Diego State University shows that teens who spent more time on social media, gaming, texting and video-chatting on their phones were not as happy as those who played sports, went outside and otherwise interacted with people, in person.

It makes sense. Smartphones and other personal electronic devices are very insular, a situation demonstrated every time a video shows up online of a smartphone user so absorbed in an e-task that he or she walks into a fountain or crashes into a glass door.

The survey involved a compilation of data collected from more than a million eighth, 10th and 12th-graders.

One of the more amusing — and relevant — online posts we’ve seen on this subject shows a group of five or six high school kids on a sidewalk, probably on their way home from school, and each of them is two-handing a smartphone and gazing, transfixed, into its display. The caption nails the moment so perfectly — “The new zombie apocalypse.”

The survey was mostly raw data, and the research team never really decided whether the phenomenon is a function of generally sadder kids isolating themselves in a virtual world, or maybe a different kind of brain function.

The problem for parents is that taking away the phone when the teen shows signs of depression usually only makes matters worse. It is most pronounced in young people who text a lot. We know of one teen who was texting at the rate of thousands of messages a week, dropped her phone and broke it, then spiraled into deep depression. Mom bought her a new phone. Problem solved.

Or was it? A separate study by the U.S. Centers for Disease Control and Prevention found a spike in depression and suicide among teen girls directly linked to the time they spent on their phones. The more time on the phone, the more likely the depression.

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This information is more important than you might think. Kids are getting smartphones at a younger age, dropping from 12 in 2012, to just more than 10 years of age in 2016. The most dramatic change in teen behavior related to smartphone use occurred in 2012, which is about when younger kids started spending more time glued to their phones. Researchers also found that teens' life satisfaction, self-esteem and happiness have plummeted since 2012.

What can parents do about this? Taking the phones could make behavioral matters worse — unless we can somehow convince the young users to seek personal satisfaction in some other way. Getting involved in sports is a sure-fire picker-upper, but not everyone is inclined to make the sacrifices necessary to enjoy competitive sports.

The San Diego State research team made a few suggestions, and this could work: Limit your teen to no more than two hours a day on digital media, exercise more and try to hang out with friends face-to-face to increase happiness.

In fact, that’s pretty solid advice for people of all ages. We’ve focused on the happiness issue with teens, but most adults we know could spend a little less time on their devices. There’s nothing sadder than seeing two adults at dinner, but instead of chatting, they’re texting.