But once the researchers compared twins within the same family, most of these associations shrank. The weakening was sharpest among identical twins, who share nearly all of their genes.

"The correlations did not disappear entirely, but they did become significantly weaker, suggesting that both genes and upbringing play an important role," says Tong Gong, research specialist at the Department of Medical Epidemiology and Biostatistics at Karolinska Institutet. Gong and senior researcher Lu Yi are the study's corresponding authors.

Does this mean screens don't affect mental health?

No, and the team says so plainly. Even after accounting for shared family factors, interactive screen use during adolescence still tracked with a higher risk of mental health problems later on, though the statistical uncertainty grew.

"Our results suggest that the association may in some cases have been overestimated because it has not been possible to fully account for shared family factors," Gong says.

What are the main limitations?

Three caveats stand out:

• The screen-use data came from self-reports, not objective measurement.
• The records do not capture exactly what young people were doing on their screens or why.
• The data was collected before social media and smartphones became as integral a part of young people's daily lives as they are today.

What happens next?

The researchers plan to dissect specific activities, the content viewed, the motivation behind it, and whether screen time crowds out other behaviors. They also want to see how the patterns differ across age groups and between girls and boys.

"Future recommendations should not focus solely on how much time children and young people spend in front of screens," says Emma Frans, senior research specialist at the same Karolinska department and a co-author. "To be able to give good advice, we also need to understand what they are doing on their screens, why they are doing it and which individual and family-related factors may affect their well-being."

The takeaway for parents and policymakers: heavy interactive screen use during the teen years still correlates with later depression and anxiety, but a chunk of that link appears to come from the genes and home environment young people already share — not just from the screens themselves.