Is all that time on screens damaging young people's mental health? On 8 October 2026, researchers at Karolinska Institutet in Sweden published a study in Nature Human Behaviour. By comparing twins with each other, they found that much of the link between screen time and depression or anxiety seems to come from factors that families share, rather than from screens alone. The answer is not "screens are harmless", and it is not "screens are poison" either.
Why Twins?
Most studies compare different young people: heavy screen users versus lighter users. But these groups also differ in their genes, home life, income and stresses. Some of these factors can push a young person towards both more screen time and lower mood, creating a link that screens did not cause.
Twins offer a way around this. They grow up in the same family; identical twins share virtually all their genes, non-identical twins about half on average. If one twin uses screens much more than the other and also has more symptoms, that difference cannot come from anything the twins share. This is called a co-twin control design (we explain how twin studies work in our article on ADHD, genetics and trauma).
What the Researchers Did
The team, with corresponding authors Tong Gong and Lu Yi, used the Child and Adolescent Twin Study in Sweden (CATSS): 21,797 twins born in Sweden from 1992 onwards, surveyed at ages 9, 15, 18 and 24, with data collection starting in 2004. The data were linked to national registers, showing who was later diagnosed with depression or an anxiety disorder, or prescribed an antidepressant.
Screen use was split into interactive activities (gaming, chatting, browsing the internet) and passive ones (watching TV or videos).
What They Found
- In the whole group, the familiar link appeared. At 15 and 18, more screen time went with more depressive and anxiety symptoms. Those using screens more than six hours a day scored clearly higher than those using them two hours or less, and the gap was larger in girls.
- Interactive use mattered most. Fifteen-year-olds with more than six hours a day of interactive use were two to three times more likely to be diagnosed with depression or anxiety, or prescribed an antidepressant, by age 28. Passive viewing showed no clear link with these outcomes.
- Within twin pairs, the links shrank. Comparing identical twins, the associations with symptoms at 15 were 32% to 95% smaller and no longer statistically significant once multiple testing was taken into account. For later diagnoses, within-pair estimates fell by 57% to 59%.
"The association may in some cases have been overestimated," said Tong Gong in the Karolinska Institutet press release.
Not "Screens Are Harmless" Either
Even within twin pairs, most estimates stayed above zero. Heavy weekday interactive use at 15 still corresponded to a 65% higher risk of a later diagnosis after accounting for family factors, although this was no longer statistically significant. The authors' conclusion: shared family factors explain a substantial part of the link, a small direct effect cannot be ruled out, and heavy recreational screen use remains a public health concern.
What a Twin Design Can and Cannot Rule Out
A co-twin comparison removes what twins share: genes (fully for identical twins, half for non-identical ones), upbringing and home environment. It does not remove what differs between them, such as friends, bullying, sport or experiences at school, and it cannot fully settle what comes first. Few twin pairs differ strongly in screen use, and errors in self-reported screen time tend to push within-pair estimates towards zero, so a modest real effect could be hidden.
Timing matters too. Data collection began before smartphones and social media became central to young people's lives, and screen use was measured as broad hours per day.
Small Average Effects, Real Individual Difficulties
In 2019, Amy Orben and Andrew Przybylski of the University of Oxford analysed three large datasets covering more than 355,000 adolescents, also in Nature Human Behaviour. The association between digital technology use and well-being was negative but small, explaining at most 0.4% of the variation. In the same data, regularly eating potatoes showed a similar association, and wearing glasses a stronger one.
But a small average does not mean screens are fine for everyone. Averages can hide people for whom use becomes hard to control: staying on longer than intended, losing sleep, neglecting other things, or using screens mainly to escape difficult feelings (our article on dopamine and reward seeking looks at why some activities are so hard to put down). That is what the Karolinska researchers want to study next: content, motivation, problematic use and what screen time replaces. Co-author Emma Frans argues that good advice must look at what young people actually do on screens, not only at how long.
What This Means for You
- Look at how, not only how much. "Can I stop when I want?", "Is it eating into my sleep?" and "Am I using it to avoid how I feel?" often say more than hours.
- No blame. "Shared family factors" includes genes and circumstances nobody chooses. The study is not about bad parenting; it shows that screen habits and mood are shaped by many things at once.
- Take symptoms seriously in their own right. If you or a young person close to you feels persistently low or anxious, that deserves attention whatever the screen time; a doctor or mental health professional is the right person to talk to.
To look at your own relationship with screens, our free screen dependence test, based on the Internet Addiction Test (20 questions, about 10 minutes), focuses on control, sleep, mood and daily life rather than hours alone. And if difficulty stopping is part of a longer-standing pattern of distraction, restlessness or impulsivity, the free ASRS-v1.1 adult ADHD screener (18 questions, about 10 minutes) may help. Screening tests are not a diagnosis, but they can help you start a conversation with a professional.
Source: Gong T, Frans E, Ohlis A, Yao S, Zhang R, Nilsson A, Molero Y, Mosing MA, Brikell I, Larsson H, Lichtenstein P, Thorell LB, Magnusson PKE, Kuja-Halkola R, Lu Y (Karolinska Institutet, Sweden). Recreational screen use and internalizing problems from preadolescence to young adulthood in a longitudinal twin cohort with co-twin comparison. Nature Human Behaviour, published online 8 October 2026, DOI 10.1038/s41562-026-02607-0 (open access). Longitudinal cohort with co-twin control design: 21,797 twins from the Child and Adolescent Twin Study in Sweden (CATSS), surveyed at ages 9, 15, 18 and 24 and linked to national patient and prescription registers. Background: Orben A, Przybylski AK. The association between adolescent well-being and digital technology use. Nature Human Behaviour 3:173-182 (2019), DOI 10.1038/s41562-018-0506-1 (specification curve analysis of three datasets, 355,358 adolescents).