Science

Survey raises worries about how screen time affects kids brains

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Nearly two out of three U.S. kids spend more than two hours a day looking at screens, a new analysis of activity levels finds. And those children perform worse on memory, language and thinking tests than kids who spend less time in front of a device, the study of over 4,500 8- to 11-year-olds shows.

The finding, published online September 26 in Lancet Child & Adolescent Health, bolsters concerns that heavy use of smartphones, tablets or televisions can hurt growing minds. But because the study captures a single snapshot in time, its still not known whether too much screen time can actually harm brain development, experts caution.

Researchers used data gleaned from child and parent surveys on daily screen time, exercise and sleep, collected as part of a larger effort called the Adolescent Brain Cognitive Development Study. Cognitive abilities were also tested in that bigger study. As a benchmark for the new study, the researchers used expert guidelines set in 2016 that recommend no more than two hours of recreational screen time a day, an hour of exercise and between nine and 11 hours of nighttime sleep.

Overall, the results are concerning, says study coauthor Jeremy Walsh, an exercise physiologist who at the time of the study was at the Childrens Hospital of Eastern Ontario Research Institute in Ottawa, Canada. Only 5 percent of the children met all three guidelines on screen time, exercise and sleep, the survey revealed. Twenty-nine percent of the children didnt meet any of the guidelines, meaning that “theyre getting less than nine hours of sleep, theyre on their screens for longer than two hours and theyre not being physically active,” Walsh says. “This raises a flag.”

On average, the children in the study spent 3.6 hours a day using screens for video games, videos and other fun. Children who spent less than two hours on screens scored, on average, about 4 percent higher on a battery of thinking-related tests than the kids who didnt meet any of the screen, exercise or sleep guidelines, the researchers found.

“Without consideration of what kids are actually doing with their screens, were seeing that the two-hour mark actually seems to be a good recommendation for benefitting cognition,” says Walsh, who is now at the University of British Columbia in Okanagan.

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Kids who met the recommendations for both screen time and sleep tested better as well. When analyzed on their own, sleep and physical activity didnt seem to influence test results.

The study cant say whether screen time — or the resulting absence of other activity — lowered thinking skills in children. “You dont know which is the chicken and which is the egg here,” cautions pediatrician Michael Rich of Boston Childrens Hospital. It could be that smarter kids are less likely to spend lots of time on screens, he says.

Looking for clear-cut blame is a bit of a “red herring,” Rich says. Simple cause-and-effect relationships often dont exist in human behavior and development. Instead of blanket pronouncements, “we need to tailor what we learn from science to individual children.”

By looking at behaviors in combination, the results offer a comprehensive look at childrens health, one thats sorely needed, says Eduardo Esteban Bustamante, a kinesiologist at the University of Illinois at Chicago. “We dont know a lot yet about how these behaviors interact with one another to influence kids cognitive development,” he says.

The Adolescent Brain Cognitive Development Study is slated to continue collecting similar data from these families until 2028. “Im really excited to see where this line of research goes,” Bustamante says.

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