Long-term study links childhood screen time to slightly better cognitive skills in teenagers

A long-term assessment of physical habits from childhood to adolescence suggests that higher amounts of screen time and lower amounts of unsupervised physical activity are associated with better cognitive performance in teenage years. The findings, published in Pediatric Exercise Science, highlight how different types and measures of daily movement relate to brain development in unexpected ways.

Cognition refers to a set of high-order mental processes that allow us to navigate daily life. These processes include working memory, which involves holding and manipulating information over short periods, attention, which is the ability to focus, and psychomotor speed, which is how quickly the brain processes and reacts to a stimulus. Childhood and adolescence are sensitive periods for the development of these cognitive skills.

During these formative years, physical activity often decreases while sedentary behaviors and screen time tend to rise. Past research exploring how these shifting habits affect the developing brain has yielded mixed results. Some studies suggest that physical activity boosts cognition by increasing blood flow and releasing beneficial brain chemicals, while others find no such link.

There is also a growing understanding of how broader physical health outcomes influence the brain. For example, a study covered by PsyPost in 2024 indicated that physical health factors like stiffer arteries are associated with weaker working memory in teens. To better understand the daily habits that often drive these physical outcomes, researchers wanted to look at long-term, cumulative exposure to both physical activity and sitting time.

Prior studies had largely relied on snapshots of behavior at a single point in time. “Existing studies on adolescents have reported mixed findings on how physical activity, sedentary time, and screen time relate to cognition,” Petri Jalanko, a doctoral researcher at the University of Jyväskylä, told PsyPost.

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“Most prior work has focused on a single time point, even though children’s movement behaviors change substantially as they grow,” Jalanko added.

To address this gap, the research team, led by Jalanko, tracked the cumulative impact of these movement behaviors over many years. They drew on data from the Physical Activity and Nutrition in Children study in Finland, analyzing a sample of 260 adolescents who were initially recruited between the ages of 6 and 9.

Over an eight-year period, the participants underwent assessments at a baseline visit, a two-year follow-up, and an eight-year follow-up. The researchers also wanted to compare data from self-reported questionnaires with objective data gathered by wearable fitness devices, as the two methods often capture different aspects of physical behavior.

To capture physical activity and sedentary behavior, the researchers used two distinct methods. First, participants and their parents filled out questionnaires detailing the frequency and duration of various activities. This included organized sports, unsupervised physical activity, screen time, and non-screen sedentary time, such as reading or doing arts and crafts.

Second, the children wore a specialized monitor on their chests for a minimum of four consecutive days at each of the three assessment periods. This device recorded heart rate and body movement to objectively measure time spent in light, moderate, and vigorous physical activity, as well as total sedentary time.

At the final eight-year follow-up, when the adolescents were around 15 to 17 years old, they completed a computerized cognitive test battery. This testing software measured their reaction times and accuracy across tasks designed to evaluate psychomotor function, attention, working memory, and associative learning.

The self-reported data yielded some surprising associations. Accumulating more unsupervised physical activity over the eight years was associated with poorer working memory accuracy in adolescence. The authors noted that this specific link was relatively weak from a statistical standpoint, but it presented an interesting contrast to common assumptions about exercise.

“We were also intrigued by the finding that some types of physical activity context (for example, unsupervised activity, as defined in our measures) showed a negative association with working memory,” Jalanko said. “That result should be interpreted cautiously and needs replication, because it may reflect unmeasured factors—such as what the activity is displacing (sleep, homework), or differences in social/educational context—rather than an adverse effect of activity itself.”

More self-reported screen time over the years was linked to faster reaction times in working memory tasks and better overall cognitive scores. Similarly, higher amounts of self-reported non-screen sedentary time were associated with faster reaction times, though this came at the cost of poorer accuracy on working memory tasks.

“One result that stood out was that more screen time was associated with better cognition in our models, because public discussion often assumes screen time is uniformly harmful,” the researcher noted.

“In our data, higher screen time was associated with slightly better performance on some cognitive measures at age 16,” Jalanko explained. “This does not mean that ‘more screen time makes teens smarter’—screen time is a broad category, and different content and contexts likely matter a lot.”

Instead, some screen activities, such as schoolwork, learning-oriented use, or cognitively engaging hobbies, might support or reflect cognitive skills. “More broadly, families shouldn’t view screen time as automatically harmful in all cases, but it’s still important to keep a healthy balance: protect sleep, make room for physical activity, and encourage screen use that involves active thinking rather than passive scrolling,” Jalanko said.

The objective data recorded by the chest monitors showed a different picture. Overall, cumulative device-assessed physical activity and sedentary time were not related to cognitive performance in the general group of adolescents. The physiological intensity of movement, recorded purely by heart rate and acceleration, did not show a broad association with brain function.

When the researchers looked at boys and girls separately, distinct patterns emerged. For boys, engaging in more self-reported organized sports was related to better working memory. At the same time, more self-reported unsupervised physical activity was linked to poorer working memory in boys, but not in girls.

For girls, higher amounts of self-reported screen time were associated with better overall cognition, a pattern not seen in the boys. Additionally, the objective device measurements indicated that more light physical activity was associated with better working memory in girls, but not in boys.

As with all research, there are some caveats to consider. Because cognitive tests were only fully administered at the end of the eight-year period, the researchers cannot determine cause and effect.

“This was an observational longitudinal study, so we cannot conclude that screen time causes changes in cognition,” Jalanko emphasized. “In terms of practical importance, the observed associations were small—they are meaningful for understanding population patterns, but cognition is influenced by many factors (sleep, education, family environment, mental health, etc.), and screen time is only one part of that picture.”

It is possible that children with naturally stronger cognitive skills simply choose to spend more time on certain screen-based tasks or less time on unsupervised physical play. The study also relies heavily on how behaviors are categorized.

“‘Screen time’ includes many very different activities; some may be beneficial or neutral, and others may be harmful,” Jalanko pointed out. “So it would be a misinterpretation to take our findings as a recommendation for unlimited or purely entertainment-focused screen use.”

He added that prior research suggests that highly passive or rapidly changing short-form content might relate differently to brain health outcomes than educational or interactive use. There are also limitations related to how the behaviors were measured.

Questionnaires rely on memory, which can introduce errors. Parents might not know exactly how much time their child spends playing unsupervised, or they might underestimate screen time. On the other hand, chest-worn devices cannot tell the difference between sitting down to read a book and sitting down to watch a movie.

The researchers suspect that the context of the activity plays a major role in these results. Activities grouped under screen time or sedentary time often include cognitively stimulating tasks, such as reading, doing homework, playing strategy-based video games, or socializing with friends. Unsupervised physical activity might actually replace time that could otherwise be spent on these mentally engaging tasks.

Future studies will need to track both physical behavior and cognitive performance repeatedly from early childhood into adulthood. This approach would help scientists map out exactly how daily habits and brain development interact over a lifetime.

“A key next step is to move beyond observational associations and test causality more directly,” Jalanko told PsyPost. “We are currently analyzing data from our VERNA randomized cross-over study to examine how different intensities of physical activity affect cognitive performance acutely in adolescents.”

“Together, the longitudinal and experimental approaches can help triangulate which relationships are likely causal, and under what conditions,” he concluded.

The study, “Associations of Physical Activity and Sedentary Time From Childhood to Adolescence With Cognition in Adolescence: The PANIC Study,” was authored by Petri Jalanko, Marja H. Leppänen, Bert Bond, Jari A. Laukkanen, Timo A. Lakka, and Eero A. Haapala.