To no parent’s surprise, too much smartphone use makes teens unhappy.

So says a new study from San Diego State University, which pulled data from over one million 8th-, 10th-, and 12th-graders in the U.S. showing 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 interacted with real human beings.

But is it the screen time bringing them down or are sadder teens more likely to insulate themselves in a virtual world? Lead author of the study and professor of psychology Jean M. Twenge believes it’s the phone that contributes to making them unhappy, not the other way around.

“Although this study can’t show causation, several other studies have shown that more social media use leads to unhappiness, but unhappiness does not lead to more social media use,” Twenge said.

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