Twin study weakens simple link between screen time and teen mental health

A study of 21,000 Swedish twins suggests that genetics and family environment help explain the link between heavy interactive screen use and anxiety or depression.

A Swedish study from Karolinska Institutet adds nuance to a debate that has often been framed too simply: screen time and mental health are linked, but the relationship is not straightforward. The research followed about 21,000 twins from the age of nine and found that young people who spent more time on screens tended to report more symptoms of anxiety and depression. But when researchers compared twins raised in the same family, the connection weakened, suggesting that inherited traits and shared home environment also shape the outcome.

According to Emma Frans, one of the study’s authors and a researcher in medical epidemiology at Karolinska Institutet, the findings show that screen use cannot be treated as the only explanation for mental health problems in children and teenagers. The study looked at both diagnosed conditions and self-reported symptoms, using information from registers and questionnaires, while screen time was reported by the children or their parents. Frans said the results indicate that what matters is not just how long a child is online, but also what they are doing and what those activities may be replacing.

The clearest associations appeared among teenagers who spent long periods gaming, chatting or browsing. By contrast, passive viewing, such as watching television, showed very weak or no clear link with psychological distress. In the overall results, 15-year-olds who spent more than six hours a day on interactive screen activities were more likely to report symptoms of depression or anxiety than peers who used screens for no more than two hours a day.

The family comparison brought an important correction to that broad pattern. Once the researchers compared twins within the same household, many of the associations became much smaller, especially among identical twins. That points to a mixture of influences rather than a single cause. As Frans put it, the issue is complex and probably depends on both genetics and upbringing, as well as on the kinds of activities that screen time displaces, such as sleep, exercise or face-to-face social contact.

The study was published in Nature Human Behaviour and is part of a broader body of research at Karolinska Institutet examining screen time effects on adolescent mental health, including depression, anxiety and suicidality. The institute says the effects are generally small, but may still matter for some young people. Related systematic reviews have also found links between heavy screen use and poorer mental well-being in adolescents, although researchers increasingly stress that content, context and the amount of time spent outdoors all matter when assessing risk. The Swedish team says its earlier findings should now be followed by more detailed work on what children and teenagers actually do on their devices.