Limiting children to less than two hours a day of screen time is associated with better brain function, including memory, attention and the speed with which new information is processed, according to a new study.

And when that limited screen time is coupled with a good night’s sleep — at least nine hours a night — children tend to score even better on cognitive tests, the study also found.

“These findings highlight the importance of limiting recreational screen time and encouraging healthy sleep to improve cognition in children,” write the authors of the study, which was published online last week in the journal Lancet Child & Adolescent Health.

The study’s authors urge parents, teachers, physicians and policymakers to “promote limiting recreational screen time and prioritising healthy sleep routines throughout childhood and adolescence.”

Study details

For the study, Canadian researchers at the Children’s Hospital of Eastern Ontario Research Institute analyzed data collected from 4,524 American children, aged 8 to 11 years, who were participants in a large, long-term study of brain development and child health. The children came from 21 different locations across the United States.

At the start of the study, the children’s parents answered questions about their child’s health-related activities, including screen time (TV, smartphones, tablets and video games), sleep patterns and physical activity.

In addition, each child was given a cognitive test that assessed such brain functions as attention, working memory, episodic memory, language skills and processing speed.

The researchers wanted to see if the recommendations in Canada’s “24-hour Movement Guidelines for Children and Youth” are effective in ensuring good cognitive development in children. Those recommendations urge parents to make sure their children get nine to eleven hours of sleep per night, less than two hours of recreational screen time per day, and at least an hour of physical activity daily (including at least three days per week of vigorous activity).

Key findings

The children in the study averaged 3.6 hours of recreational screen time each day. They slept an average of 9.1 hours per night.  In addition, they engaged in at least one hour of moderate to vigorous physical activity on an average of 3.7 days per week.

Half of the children (51 percent) met the sleep recommendation, 37 percent met the screen time recommendation, and 18 percent met the physical activity recommendation.

Very few of the children — 5 percent — met all three recommendations, and almost 30 percent met none of them.

When the researchers compared how well children met the three recommendations with their cognitive test scores, they found children who met all three recommendations tended to score highest on the tests.

Furthermore, higher results were most strongly linked with meeting the screen-time recommendations alone or in combination with the sleep recommendation.

“This finding raises the possibility that daily recreational screen use in excess of 2 [hours] attenuates the benefits of sleep for cognition,” the study’s authors write.

All results held even after adjusting for other factors known to be associated with how well children do on cognitive tests, such as household income, parent education level, body mass index and history of a head injury.

Surprisingly, meeting only the physical activity recommendation was not associated with higher scores on the cognitive tests. That finding, say the study’s authors, may be explained by the way parents were asked to categorize their child’s physical activity.

“Irrespective of our findings,” the authors stress, “physical activity remains the most important behaviour for physical health outcomes, and there is no indication in the literature that it negatively affects cognition.”

Limitations and implications

The study comes with many of the usual caveats that accompany an observational study. It can show only a correlation between screen and sleep time and brain function, not a direct cause-and-effect. Factors not accounted for in the analysis may explain the study’s results.

Furthermore, the data used in the study was collected only once, not over time.

Still, the results support other evidence that suggests children perform better cognitively when their screen time is limited and their sleep time is maximized.

Digital screen technology can deliver educational and enriching content, but spending too much time with that technology may also be harmful for children, this broader body of research is finding.

“Each minute spent on screens necessarily displaces a minute from sleep or cognitively challenging activities,” writes Eduardo Esteban Bustamante, a behavioral scientist at the University of Illinois, in a commentary that accompanies the study.“In the case of evening screen use, this displacement may also be compounded by impairment of sleep quality.”

“It is tempting to take solace in findings that cognitively challenging screen activities can benefit cognition,” he adds, “but, if given a choice, most children already consistently and predictably choose more stimulating screen activities over less stimulating ones.”

FMI:  An abstract of the study and editorial can be found on the website for the Lancet Child & Adolescent Health, but the full papers are being a paywall.