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For years, experts have pointed a finger at phones as a possible factor in depression and other mental health problems. A study published Monday from researchers at Montreal's Sainte-Justine Hospital found that increased social media and TV use predicts an increase in symptoms of depression in teenagers.

"Our research reveals that increased time spent using some forms of digital media in a given year predicts depressive symptoms within that same year," Patricia Conrod, the research team's lead said, in a press release on Monday.

Conrod's team followed about 4,000 Canadian teenagers, aged 12 to 16 years, for four years. For each year of high school, teens self-reported on time spent with digital screens. They specified the amount of time spent participating in four different types of screen activities: social media, television, video gaming and computer use. The study found that if teens reported increases that their social media use and television viewing, then their depression symptoms also increased. However, an increase in video gaming wasn't found to be a predictor for depression.

Conrod said more research is needed to tell whether exposure to social media is actually causing elevated rates of depression in young people, but said the study could help design intervention strategies for at-risk youths.

"Early identification of vulnerability to depression gives clinicians and parents a large window of time in which to intervene," Conrod said. "Regulating teens' social media and television use might be one way to help young people manage depressed mood or vulnerability to depressive symptoms."

Conrod wasn't immediately available for additional comment.