Whether heavy screen use itself increases the risk of mental illness, or whether young people with mental health problems spend more time on screens, is a matter of debate.
Researchers at the Karolinska Institute have followed 21,000 Swedish twins from the age of nine and can now draw some conclusions.
"We saw a connection between screen time and mental health. But when we compared twins in the same family, screen time was not linked nearly as strongly to mental health," says Emma Frans, a researcher in medical epidemiology and one of the study authors.
Depression and anxiety
By comparing twins in the same family, where one twin used screens more than the other, the researchers were able to examine how genetic factors and upbringing influenced the relationship. The children were followed through adolescence and into adulthood.
The researchers also tracked symptoms of anxiety and depression, partly through diagnostic registers and partly through self-reported questionnaires. Screen time was reported by the participants or their parents.
The clearest links between screen use and mental health were seen among teenagers who played games, chatted and surfed the web. Very weak or no links were seen for passive activities such as watching TV.
Overall, the results, published in Nature Human Behaviour, showed that 15-year-olds who spent more than six hours a day on interactive screen activities had more symptoms of depression or anxiety than peers who spent no more than two hours a day using screens.
The influence of the upbringing environment
But when the researchers compared twins within the same family, most of the associations weakened, especially among identical twins. This suggests that both heredity and upbringing play a role.
There is a lot of talk about screen time and mental health, and what we see is that many factors influence it. It is complex and is likely to be about both what you do on the screen and what activities screen time replaces, says Emma Frans.
The first twins followed were born in 1992, so their screen use is very different from that of those born later. In future studies, Emma Frans hopes to examine more closely how children and young people are affected by what they do on screens.
The researchers have followed more than 21,000 Swedish twins from the age of nine, through adolescence and into adulthood. The first participants included in the study were born in 1992.
Data was collected via questionnaires and telephone interviews with parents and twins about screen use, environment, behavior, and physical and mental health.
The researchers have also used national registers to track diagnoses, medication use and mortality for some of the study participants.
The study does not capture exactly what the young people did on screens or why they used them.
The study was mainly funded by the Marianne and Marcus Wallenberg Foundation and the Swedish Brain Foundation.
Source: Nature Human Behaviour and Karolinska Institute