What two new studies found about children and screens - critical summary review

What "screen time" research is actually trying to measure

When researchers talk about screen time, they are not measuring one behaviour. The category lumps together a toddler on a FaceTime call, a teenager scrolling social media, a ten-year-old gaming and a family watching television. That breadth is why the field has produced so many contradictory headlines over the past decade, and why parents keep hearing new "safe" limits that never quite hold.

Two things make these studies hard. The first is that almost none of them can prove causation: a child who spends more hours on a tablet may also come from a household under more stress, with less sleep, fewer books or a parent working two shifts. The second is that most of the research asks how much, which is the question a household can answer with a stopwatch, while the more awkward question is from what age.

That is the backdrop for two studies published in the same week, both in journals of the American Medical Association, that give numbers to a suspicion many families and schools have been carrying without evidence. For anyone deciding when a child gets a phone, or drafting a school policy on devices, they shift the terms of the argument.

What the two studies measured, and what they found

The first, published in the journal JAMA Pediatrics and led by academics at the University of Calgary in Canada, examined data on more than 2.8 million children across 64 countries. The Guardian described it as one of the largest ever studies on the subject. It is what researchers call an umbrella review: rather than collecting new data, it summarises the results of previous large reviews, covering devices from smartphones to televisions and activities from scrolling to gaming to video calls.

The finding was that longer durations of digital and social media use were linked to "less favourable outcomes across multiple (although not all) measured domains of children's developmental health". In plainer terms: higher screen exposure was associated with lower overall grades at school, poorer language development, emotional and peer problems, symptoms of depression and anxiety, and aggression and attention deficit hyperactivity disorder symptoms.

One detail matters for teachers reading this. When the researchers looked at specific subjects, screen time did not appear to be linked to attainment in maths, reading or science. Their own explanation was that these were "among the least studied", so the absence may reflect a lack of evidence rather than an absence of effect.

The second study, published in JAMA Network Open, came from a survey of nearly 9,000 adolescents across the United States, drawn from the Adolescent Brain Cognitive Development Study, a long-term study of brain development and health in American children. It asked a different question: not how many hours, but at what age the phone arrives.

The size of the effect, and why that is the striking part

The Calgary authors wrote that the associations they found were "similar in magnitude to or larger than those reported for other well-established predictors of children's outcomes, such as socioeconomic status, parenting behaviour and preterm birth".

That comparison is what gives the study its weight. Family wealth, parenting behaviour and premature birth are the factors paediatricians and education researchers have treated for decades as the serious predictors of how a child will do. Screen exposure, on this reading, sits in the same range. The authors also noted what makes it different: unlike prematurity or household income, "screen use may represent one potentially modifiable factor associated with children's wellbeing across multiple domains". It is the item on that list a family or a school can actually change.

Age of first phone: 12 and 14

The American study followed children from age 12 to 14. Among the 12-year-olds surveyed, 70% owned their own phone. Of those, 24% reported at least one eating disorder symptom at 14. Among the teens who did not have a smartphone at 12, fewer than 16% reported disordered eating two years later.

The study also found that children who had smartphones at 12 were twice as likely to tie their self-worth to their weight, and one and a half times more likely to have tried controlling their weight by, for example, eating low-calorie foods or exercising a lot.

Dr Jason Nagata, the study's lead author and an associate professor of paediatrics at the University of California, San Francisco, framed it this way: "A smartphone can put a world of appearance-focused content in a young person's pocket." He told CNN that getting a phone "isn't just about the device. It can change a child's access to different content and exposures in the digital world." Before smartphones, he said, the comparisons children made were mainly with peers. "But when you're comparing yourself to influencers whose images are curated, edited and filtered, that can lead to more body dissatisfaction and poor self-esteem, and then that can be a risk factor for eating disorders."

Two other figures from his lab sharpen the picture for anyone setting rules. Most major social media platforms set 13 as the minimum age to open an account, yet Nagata's past research found that nearly two thirds of 11- and 12-year-olds have accounts on platforms such as TikTok and Instagram. And around 22% of children and adolescents worldwide show signs of disordered eating, according to research estimates.

What the studies do not prove

Both studies describe associations, and specialists quoted by The Guardian were direct about the limits.

Tatiana Íñiguez Berrozpe, a senior lecturer in sociology at the University of Zaragoza in Spain, said the review did show a link between screen time and poor mental health and academic performance, but that the link was small. "This is not an insignificant finding, but it in no way supports the mantra that screens are the main cause of adolescent emotional distress," she said. "Screen use alone does not explain why a teenager is emotionally distressed or performs less well academically."

Esther van Sluijs, a professor of behavioural epidemiology at Loughborough University in the UK, called the review high-quality but noted that it could not distinguish between kinds of screen use. "It cannot draw robust conclusions about specific types of screen use, like social media use or gaming, as there was not enough data to study this. We should therefore be cautious in interpreting these results in the context of young people's current screen use habits," she said.

Nagata himself said the study does not provide the "magic answer" as to the ideal age for a first phone.

The Brazilian backdrop

In Brazil, these numbers land in the middle of an existing public health argument. A Folha de S.Paulo editorial (the newspaper's own position, in one of the country's largest dailies) noted that the suicide of a 13-year-old girl in Naviraí, in the state of Mato Grosso do Sul, during a live video broadcast at the end of July drew attention to a problem observed in several countries: a rise over the past decade in depression, anxiety, self-harm and suicide among the youngest age groups.

The editorial cited the Health Ministry's most recent epidemiological bulletin with a historical series on the subject: between 2016 and 2021, the suicide rate among 10-to-14-year-olds grew 45%, and among 15-to-19-year-olds 49%, against 17.8% for the population as a whole. It also stressed that international research still does not allow a general causal link to be drawn between social media use and deteriorating mental health in children, while arguing that the new communication technologies can aggravate risks in vulnerable groups.

The regulatory response is already in place. What the paper calls the ECA Digital, the legislation extending Brazil's child and adolescent statute to the online environment, has been in force since March and requires platforms to prevent and mitigate risks, provide age-appropriate experiences, allow parental supervision and include settings designed to avoid compulsive use.

What is known, and what is still unknown

What is established: across 2.8 million children in 64 countries, higher screen exposure is associated with lower overall grades, poorer language development and more emotional and behavioural problems, at a magnitude the authors put alongside household income and preterm birth. Among nearly 9,000 American adolescents, owning a phone at 12 was associated with more eating disorder symptoms at 14. And whether a child has social media accounts before 13, the platforms' own minimum, is largely not being enforced by the platforms.

What is still unknown: whether screens cause any of it. Which types of use matter, since the large review could not separate gaming from social media from video calls. Whether the absence of a link to maths, reading and science attainment is real or an artefact of thin evidence. And the age question stays open too: Dr Mitch Prinstein of the University of North Carolina at Chapel Hill, who was not involved in either study, told CNN that new research is beginning to find that delaying access to phones by six months or a year appears to benefit children's mental health, and that when a child does get one, parents should allow "slowly, gradually" more exposure to social media rather than handing over "a completely unlocked phone". Nagata's suggestions for families who do give a preteen a phone were guardrails of the same kind: limiting which apps can be downloaded, keeping the phone out of the bedroom, agreeing ground rules, and watching for changes in how a child eats or talks about their body.