Twin study weakens case for screen time as a direct cause of poor mental health

A study of more than 21,000 Swedish twins suggests genes, family circumstances and upbringing explain much of the apparent link between heavy screen use and depression or anxiety.

A large new twin study suggests that the link between heavy screen use and poor mental health in young people may have been overstated, because family background, genes and shared upbringing appear to explain much of the association.

Researchers at Karolinska Institutet, reporting in Nature Human Behaviour, followed more than 21,000 Swedish twins from the age of nine into early adulthood. By comparing twins raised in the same household, including cases where one twin spent more time on screens than the other, the team set out to separate the effect of screen use itself from the influence of shared family factors.

The clearest patterns emerged during adolescence, and they were strongest for interactive activities such as gaming, chatting and browsing the internet. Fifteen-year-olds who spent more than six hours a day on those kinds of activities had more symptoms of depression and anxiety and were more than twice as likely to receive a later diagnosis of such a condition than peers who spent no more than two hours a day on screens. But once the researchers compared twins within the same family, many of those associations became much weaker, especially among identical twins, who share all of their genes.

Tong Gong, the study’s corresponding author, said the findings suggest earlier estimates may have been exaggerated because researchers have not always been able to account for the full effect of shared family circumstances. The team stressed that the results do not clear screen time entirely: even after family factors were considered, interactive screen use in adolescence still showed some association with later mental health problems, although the uncertainty around that link grew. Passive activities such as watching television or videos, by contrast, showed far weaker or no consistent relationship with depression or anxiety.

The study also fits into a broader body of research pointing to a more complicated picture than the simple idea that screen time alone drives poor well-being. A separate genome-wide study published in Scientific Reports found that screen behaviours in adolescents have a measurable genetic component and overlap genetically with psychiatric disorders, while another analysis in Humanities and Social Sciences Communications linked longer screen time in US children and teenagers with higher risks of anxiety, depression, conduct problems and ADHD, with sleep and physical activity helping to explain part of the relationship. Together, the findings suggest that what young people do online, why they do it and the routines it displaces may matter as much as the number of hours spent looking at a device.

That is why the Karolinska team says future guidance should move beyond simple screen-time limits. Emma Frans, a co-author of the study, said advice for parents and caregivers should take into account the nature of the activity, the reasons behind it and the individual and family factors that shape a child’s wellbeing. The researchers noted that their data were self-reported and were gathered before smartphones and social media became as central to young people’s daily lives as they are today, meaning the results offer an important but not final answer to one of the most debated questions in child and adolescent health.