Not only did smartphone use and depression increase in tandem, but time spent online was linked to mental health issues across two different data sets. We found that teens who spent five or more hours a day online were 71 percent more likely than those who spent less than an hour a day to have at least one suicide risk factor (depression, thinking about suicide, making a suicide plan or attempting suicide). Overall, suicide risk factors rose significantly after two or more hours a day of time online.
Of course, it’s possible that instead of time online causing depression, depression causes more time online.
… Interacting with people face to face is one of the deepest wellsprings of human happiness; without it, our moods start to suffer and depression often follows. Feeling socially isolated is also one of the major risk factors for suicide. We found that teens who spent more time than average online and less time than average with friends in person were the most likely to be depressed. Since 2012, that’s what has occurred en masse: Teens have spent less time on activities known to benefit mental health (in-person social interaction) and more time on activities that may harm it (time online).