Sedentary time spent in front of screens programs metabolism and brain neurochem. Similar to addiction.
But it’s complicated! Partly because there are so many different kinds of activity that can now be done with mobile phones and tablets, and because it’s difficult to control or randomize.
How people interact with screens is changing too. In the mid-2000s in the US, children over 8 spent an average of 6.43 hours a day on electronic media, but this was mainly watching TV. Evidence of stress response (reduced cortisol increase) on waking after using screens for average 3 hours a day.
But now mobile devices are the centre piece of young people’s social lives. Boys tend to spend more time gaming, girls more time on social networking.
Effect of high levels of screen time does not seem to be attenuated by equivalent exercise.
High levels of screen time (over 4 hours daily) is associated with poorer school performance. Social skills are poorer. These children tend to form cliques with shared interest, that create further social isolation.
Violent games and media are associated with aggression in children as young as pre-school. Aggression in children can be manifest physically, or verbally, or relationally (ignoring, excluding, spreading rumours). There is also significantly more hostile attribution bias, where you interpret behaviour (such as not being invited to a party) as hostile, even when it is not, or at least ambiguous.
Parental involvement matters – how frequently parents watch TV with their children, discuss content with them, and set limits on time spent playing video games.
Exposure to media violence must also be seen within a risks/resilience approach. [Gentile and Coyne, Aggressive Behaviour 2010] ]
Some evidence that some “social” games themed around cooperation and construction eg Animal crossing have benefits. Similarly, links between media and relational violence pretty weak, but that could be because relational violence content isn’t really examined! Actual content probably more important than time spent playing. Note that in that study of Animal Crossing, background mental health problems seemed to reduce benefit.