The study’s central innovation lies in its co-twin comparison design. Rather than simply comparing unrelated individuals, the researchers examined pairs of twins raised in the same household where one twin used screens considerably more than the other. Because identical twins share essentially all of their genes and both identical and fraternal twins share much of their family environment, differences in mental health outcomes between twins within the same pair cannot easily be attributed to those shared factors. When the researchers applied this within-family comparison, most of the observed links between screen use and mental health problems weakened considerably, particularly among identical twins, a pattern that points strongly toward genetic and environmental influences shared within families.

The clearest associations in the conventional, between-family analyses emerged during adolescence and for interactive screen activities such as gaming, chatting and surfing the internet. In contrast, the links for passive activities such as watching television or videos were significantly weaker or absent altogether. This distinction between active and passive engagement is one of the study’s most striking findings, and it complicates the simple picture of screen time as a uniform risk factor. Fifteen-year-olds who spent more than six hours a day on interactive screen activities showed more symptoms of depression or anxiety and were more than twice as likely to be diagnosed with such a condition later in life, compared with peers who spent no more than two hours a day using screens.

Those headline numbers, however, tell only part of the story. When the researchers compared twins within the same family, the strength of these associations dropped markedly. The correlations did not disappear entirely, but they became significantly weaker, suggesting that both genes and upbringing play an important role in shaping the apparent relationship. According to Tong Gong, research specialist at the Department of Medical Epidemiology and Biostatistics at Karolinska Institutet and the study’s corresponding author alongside senior researcher Lu Yi, the results indicate that the association may in some cases have been overestimated because it has not been possible to fully account for shared family factors in earlier research.

The implications of this methodological insight extend well beyond the specific question of screens. Much of the existing literature on digital technology and youth mental health relies on observational comparisons between unrelated individuals, which are vulnerable to confounding by any factor that differs across families. Genetic predispositions to both heavy screen use and internalising problems, parenting styles, socioeconomic conditions and household routines could all contribute to a spurious association. Twin designs, by holding these shared influences constant, provide a natural experiment that can separate within-person effects from between-family differences. The attenuation observed in this study, especially among monozygotic pairs, suggests that a meaningful share of the reported screen-mental health connection in the broader literature may reflect such confounding.

At the same time, the researchers are careful to emphasise that the findings do not mean screen time is irrelevant to mental health. Interactive screen activities during adolescence were still linked to an increased risk of mental health problems later in life, although the uncertainty around the estimates increased when shared family factors were included in the analyses. In other words, the data cannot rule out a genuine effect of heavy interactive use; they simply show that the effect, if it exists, is smaller and harder to detect than raw population-level comparisons imply. For a field that has produced widely varying estimates of harm, this nuance matters. It shifts the scientific conversation from whether screens are good or bad toward a more precise question of which activities, in which contexts, and for which individuals, may carry risk.

The study also carries important limitations that the authors acknowledge. It is based on self-reported data on screen use, which does not capture exactly what young people were doing on their screens or why they were using them. Self-reports of media habits are known to be imperfect, and the coarse categories used in the study cannot distinguish, for example, between social gaming with friends and solitary late-night scrolling. Furthermore, the data were collected before social media and smartphones became as integral a part of young people’s everyday lives as they are today, raising questions about how the findings generalise to a generation for whom mobile, algorithmically curated content is the default mode of engagement.

The research team, which included collaborators from Sweden, Norway, Denmark, Germany and Australia, plans to address these gaps in the next phase of work. The researchers intend to examine different types of screen-based activities in greater detail, studying their content, the motivation behind their use, problematic use patterns, and the activities that screen time replaces. By mapping these dimensions, they hope to gain a better understanding of how the complex relationships between digital media and well-being vary across different age groups and between girls and boys. Emma Frans, senior research specialist at the Department of Medical Epidemiology and Biostatistics at Karolinska Institutet and co-author of the study, argues that future recommendations should not focus solely on how much time children and young people spend in front of screens. To be able to give good advice, she notes, 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.

For parents, educators and policymakers, the study offers a measured rather than alarmist message. Simple time-based screen limits, the findings suggest, may be a blunt instrument if the true drivers of risk lie in the nature of the activity, the motivation behind it, or pre-existing vulnerabilities that screens merely reflect. A teenager who games intensively may be doing so for reasons that also elevate their risk of depression, and reducing screen hours alone may not address the underlying issue. At the same time, the persistence of some association even within twin pairs leaves open the possibility that heavy interactive use contributes directly to poorer mental health, particularly during the sensitive adolescent period.

The study, titled Recreational Screen Use and Internalising Problems from Preadolescence to Young Adulthood in a Longitudinal Twin Cohort with Co-Twin Comparison, was primarily funded by the Marianne and Marcus Wallenberg Foundation and the Swedish Brain Foundation. The authors note that one co-author, Henrik Larsson, has received research grants, honoraria and consultancy fees from pharmaceutical companies outside the scope of this study, while the other researchers declare no conflicts of interest. As debates over youth mental health and digital technology continue to intensify worldwide, this large-scale twin analysis adds a crucial layer of methodological rigour, reminding researchers and the public alike that correlation between screen time and psychological distress may say as much about families and genes as it does about screens themselves.

Subject of Research: The relationship between recreational screen use and internalising mental health problems in young people examined through a longitudinal twin cohort study

Article Title: Twin study sheds new light on screen time and mental health

Article References: Twin study sheds new light on screen time and mental health. (n.d.). Original publication

Image Credits: AI Generated

DOI: Not provided

Keywords: screen time, mental health, twin study, adolescence, depression, anxiety, genetics, Karolinska Institutet, Nature Human Behaviour, gaming, longitudinal study, youth well-being

The research team, led by Tong Gong and Yi Lu of Karolinska Institutet, drew on the Child and Adolescent Twin Study in Sweden, a national cohort that has tracked participants at ages 9, 15, 18 and 24. Because the cohort was linked to national patient registers and prescription drug records, the researchers could examine not only self-reported symptoms of depression and anxiety but also clinically diagnosed disorders and antidepressant dispensing over follow-up periods extending more than a decade. This combination of symptom scales and hard clinical endpoints is rare in screen time research, which has often relied on small samples and coarse self-reports.

The headline results were striking at the population level. At ages 15 and 18, screen time showed a clear dose-response pattern with internalizing symptoms: the more hours per day young people spent on screens, the higher their depression and anxiety scores. Comparing heavy users, defined as those spending more than six hours per day, with restrictive users at two hours or less, the standardized differences in symptom scores ranged from 0.20 to 0.38 in the full sample. The associations were markedly stronger in girls than in boys for interactive activities such as gaming, chatting and browsing, with heavy use corresponding to symptom elevations of 0.37 to 0.51 standard deviations in girls, compared with 0.19 to 0.22 in boys.

The clinical picture was even more dramatic. Heavy interactive screen use at age 15 was associated with a roughly two- to threefold increased risk of being diagnosed with a depressive or anxiety disorder by age 28, with weekday heavy use showing an adjusted hazard ratio of 3.37. Even daily gaming at age 9, reported by parents, was linked to a 38 percent higher risk of clinical outcomes through age 22. Passive activities such as watching television, videos and DVDs showed far weaker and mostly non-significant associations, suggesting that what young people do on screens may matter as much as how long they spend there.

But the study’s most consequential findings emerged when the researchers turned to the twin structure of their data. Monozygotic twins share essentially all of their inherited genes, while dizygotic twins share on average half, and both types share their rearing environment. By comparing one twin who used screens heavily with their co-twin who did not, the co-twin control design effectively removes confounding from shared genetics and family background, factors that ordinary observational studies cannot measure. If the screen-mental health link were purely causal, it should persist within identical twin pairs.

It did not, at least not robustly. Within discordant dizygotic pairs, effect estimates attenuated modestly. Within discordant monozygotic pairs, the attenuation was far more pronounced: at age 15, estimates shrank by 32 to 95 percent relative to the full sample and were no longer statistically significant after correction for multiple testing. At age 18, the corresponding estimates were attenuated by 16 to 45 percent. In the longitudinal analyses, the strong cross-age associations between heavy interactive use at 15 and symptoms at 18, and between use at 18 and symptoms at 24, were reduced by roughly 30 to 60 percent within twin pairs and fell below the significance threshold. The pattern of progressive but incomplete attenuation is consistent with a mixture of genetic confounding, shared environmental confounding and possibly a small residual direct effect.

The clinical outcomes told a similar story. The threefold risk elevation associated with heavy weekday interactive use at age 15 dropped by 57 to 59 percent within discordant twin pairs, leaving a point estimate of a 65 percent increased risk that no longer reached significance after multiple-testing correction. Daily gaming at age 9, which showed a significant hazard ratio of 1.38 in the full sample, showed no comparable association within discordant pairs. The authors interpret this cautiously: the analyses had limited statistical power because informative discordant pairs are few, so small direct effects cannot be ruled out entirely, but the evidence for a clear causal effect of screen time on internalizing problems is weak.

The study also probed directionality, a persistent puzzle in this field. Screen use at age 9 did not predict symptoms at 15, but heavy interactive use at 15 and 18 predicted symptoms at 18 and 24 respectively. Intriguingly, the reverse pathway also appeared: adolescents with higher depressive and anxiety symptoms at 15 showed a small but measurable increase in interactive screen use at 18, with an odds ratio of 1.04 per standard deviation of symptoms. Although modest, this reverse association suggests that vulnerable young people may gravitate toward heavier digital engagement, potentially encountering more negative social comparison and mood impacts, a dynamic documented in recent studies of adolescents with mental health conditions.

The findings carry important implications for policy. Public health agencies in several countries have issued guidelines limiting recreational screen time for children and adolescents, but these rest largely on non-causal observational evidence. The new results align with earlier genetically informed work showing that screen behaviors themselves are moderately heritable, with twin-based estimates of 20 to 49 percent, and that genetic confounding accounts for a substantial share of the apparent association between media use and mental health. They also echo the influential analyses by Orben and Przybylski, who found that per-hour effects of screen use on adolescent well-being are small; the co-twin estimates here correspond to roughly 0.03 to 0.05 standard deviations of additional symptoms per extra hour of interactive use at age 18.

Yet the authors caution against dismissing the issue entirely. Within age-18 identical twin pairs, weekend heavy interactive use was still associated with 0.26 standard deviations of additional symptoms compared with restrictive use, an effect size comparable to established risk factors such as bullying victimization and childhood maltreatment, which typically fall in the 0.2 to 0.3 range. The study also has limitations: data collection began in 2004, before smartphones and social media became ubiquitous; the crude categories of interactive and passive use do not capture the complexity of modern digital life; and self-reported screen time is known to be underreported. Sensitivity analyses adjusting for physical activity and bullying victimization left the main findings essentially unchanged. The researchers conclude that heavy recreational screen use remains a legitimate public health concern, particularly during adolescence, but that shared genetic and familial factors partly explain the link to depression and anxiety, and that future research should focus on why and how different types of digital engagement affect vulnerable young people, rather than on screen time alone.

Subject of Research: Longitudinal twin study of recreational screen use and internalizing problems from preadolescence to young adulthood

Article Title: Recreational screen use and internalizing problems from preadolescence to young adulthood in a longitudinal twin cohort with co-twin comparison

Article References: Gong, T., Frans, E., Ohlis, A., Yao, S., Zhang, R., Nilsson, A., Molero, Y., Mosing, M. A., Brikell, I., Larsson, H., Lichtenstein, P., Thorell, L. B., Magnusson, P. K., Kuja-Halkola, R., & Lu, Y. (2026). Recreational screen use and internalizing problems from preadolescence to young adulthood in a longitudinal twin cohort with co-twin comparison. Nature Human Behaviour. https://doi.org/10.1038/s41562-026-02607-0

Image Credits: AI Generated

DOI: 10.1038/s41562-026-02607-0

Keywords: screen time, mental health, depression, anxiety, twin study, co-twin control design, adolescence, genetic confounding, internalizing problems, gaming, Nature Human Behaviour, epidemiology

The research team, led by Unkyung No of Jeonju University and Sangwon Kim of Hanshin University, drew on nationally representative data from 1,380 Korean high school students, of whom 45.8 percent were female, with an analytic sample of 1,365. Rather than treating gaming onset as a single event, the investigators divided childhood and adolescence into seven onset intervals, ranging from the early elementary years through later adolescence. This design allowed them to ask a deceptively simple question with unusual statistical precision: does it matter when a child starts gaming, and does the answer change depending on which outcome you examine?

Methodologically, the study stands out for its use of a discrete-time survival mediation model estimated with Bayesian techniques in the statistical software Mplus. Survival analysis, a framework long used in medicine to model the timing of disease onset, treats the age at which a child first begins regular gaming as an event whose hazard can be predicted across successive time intervals. By embedding this event-history mediator within a mediation model, the researchers could trace indirect pathways: how a child’s sex or parental digital behaviors influence the timing of gaming onset, and how that timing in turn shapes later smartphone dependence and self-perceived academic standing. The approach reflects a growing methodological literature on mediation analysis with event-history mediators, which the authors note has only recently been formalized for empirical use.

The results reveal a striking asymmetry between the two outcomes. Gaming onset was linked to higher smartphone dependence when gaming began during middle childhood or early adolescence, a period that roughly corresponds to the upper elementary and middle school years. By contrast, early initiation of gaming during the early elementary years was associated with lower self-perceived academic standing in high school. In other words, there is no single danger zone; instead, different developmental windows carry different risks. Children who began gaming in middle childhood or early adolescence were more likely to report problematic patterns of smartphone engagement years later, while those whose gaming started earliest, in the first years of elementary school, were more likely to view their academic performance negatively as teenagers.

The authors are careful to frame smartphone dependence as a developmental vulnerability marker for problematic digital engagement rather than as a clinical diagnosis of Internet gaming disorder. This distinction matters. Internet gaming disorder, recognized in diagnostic frameworks, requires specific symptom patterns, whereas smartphone dependence in this study functions as an early-warning signal, an indicator that a young person’s relationship with digital devices has taken on compulsive characteristics. Framing the outcome this way allows the researchers to study risk pathways in a large representative sample without overextending clinical labels to adolescents who may show elevated vulnerability without meeting diagnostic criteria.

Sex and parental digital behaviors emerged as significant upstream factors, and their associations with gaming onset varied across development. The finding aligns with a substantial body of prior work documenting gender differences in gaming. Studies have repeatedly shown that boys begin gaming earlier and play more intensively than girls, and neuroimaging research has identified gender-related differences in neural responses to gaming cues, suggesting sex-specific vulnerabilities to problematic engagement. The Korean study adds a developmental dimension to this picture: the influence of sex on gaming onset was not uniform across childhood but showed interval-specific patterns, which in turn produced significant interval-specific indirect effects on the downstream outcomes.

Parental behavior, too, proved consequential. Decades of research on parental media mediation have established that how parents regulate, discuss, and model media use shapes children’s engagement with screens, and recent meta-analyses have confirmed that parental mediation is negatively associated with problematic media use among children and adolescents. Studies across multiple countries, including Korea, China, and Malaysia, have shown that parents’ own screen time and technology-related parenting practices predict young children’s screen exposure. The new study extends this literature by connecting parental digital behaviors to the timing of gaming onset, and by showing that this timing mediates later risks. Parents who model heavy device use or provide weak digital guidance, the findings imply, may inadvertently accelerate their children’s entry into gaming during the very windows when onset carries the greatest downstream cost.

The idea that timing matters resonates with research on developmental sensitivity to digital media. A widely cited 2022 analysis in Nature Communications identified windows of developmental sensitivity to social media, showing that the same exposure can have different psychological consequences depending on the age at which it occurs. The parallel work on substance use tells a similar story: age at first alcohol use is a well-established risk factor for later alcohol disorders, and early-onset drug use predicts later dependence problems. The Korean gaming study effectively imports this onset-timing logic into the digital domain, and its results suggest that gaming follows a pattern familiar from addictive behaviors: earlier entry, particularly during sensitive developmental periods, forecasts later difficulty regulating engagement with related technologies.

The connection between gaming onset and self-perceived academic standing deserves particular attention. Academic self-concept, the way students evaluate their own scholastic competence, is known to predict school adjustment, motivation, and long-term achievement, and it begins forming early in elementary school. A randomized controlled study of video-game ownership among young boys found that console ownership was followed by lower academic performance, and longitudinal research has generally found that heavy gaming time modestly jeopardizes educational outcomes. The new findings add nuance: it is not merely how much adolescents play, but whether gaming entered their lives during the early elementary years, when academic identities are still crystallizing, that best predicts a negative view of their school performance in high school.

For policymakers and educators, the practical implications are clear. Anti-addiction regulations, digital literacy curricula, and parental guidance programs are typically deployed as one-size-fits-all measures, but the study’s central message is that interventions should be developmentally timed. Efforts to delay gaming onset and to equip parents with effective mediation strategies may yield the greatest benefit if concentrated in the early elementary years, before academic self-concept hardens, and again in middle childhood and early adolescence, when onset most strongly predicts later smartphone dependence. South Korea, one of the most digitally saturated societies in the world and home to near-universal high-speed internet infrastructure, offers a revealing test case, and national surveys there have documented rising gaming engagement among children and adolescents. As smartphones continue to colonize childhood across the globe, the study’s message travels well beyond Korean borders: the question of when a child’s gaming life begins is not a trivial family scheduling matter, but a developmentally consequential event whose effects ripple through adolescence, shaping both the compulsive pull of the pocket-sized screen and the quiet confidence with which a teenager sits down to study.

Subject of Research: How sex, parental digital behaviors, and the timing of childhood gaming onset relate to smartphone dependence and self-perceived academic standing in adolescence.

Article Title: When Gaming Begins Matters: Sex, Parental Digital Behaviors, and Gaming Onset as a Pathway to Smartphone Dependence and Self-perceived Academic Standing

Article References: When Gaming Begins Matters: Sex, Parental Digital Behaviors, and Gaming Onset as a Pathway to Smartphone Dependence and Self-perceived Academic Standing. (n.d.). https://doi.org/10.1007/s11469-026-01722-3

Image Credits: AI Generated

DOI: 10.1007/s11469-026-01722-3

Keywords: gaming onset, smartphone dependence, parental digital behaviors, sex differences, developmental windows, self-perceived academic standing, adolescents, Korea, survival mediation model, problematic media use, Gaming, Begins