By Dennis Thompson
WEDNESDAY, Sept. 26, 2018 (HealthDay News) -- If you're worried that too much "screen time" could be sapping your child's intelligence, new research suggests you might be right.
Kids with the sharpest intellects spent less than two hours a day on their cellphones, tablets and computers, coupled with 9 to 11 hours of sleep and at least an hour of physical activity, the study found.
Unfortunately, very few U.S. children meet all three of these daily goals, said lead researcher Jeremy Walsh, a postdoctoral fellow with the CHEO Research Institute in Ottawa, Canada.
"Only 5 percent of our sample met all three guidelines," Walsh said.
About 41 percent met one of the guidelines and 25 percent met two, he continued.
"That means 30 percent of our sample didn't meet any of the guidelines, which I think is a very important statistic to focus on," Walsh said.
The study is based on data gathered from over 4,500 U.S. kids aged 8 to 11 between September 2016 and September 2017 as part of a new, federally funded 10-year study on brain development and child health.
Half of the children got the recommended 9 to 11 hours of sleep, 37 percent met the screen time guideline of less than two hours, and 18 percent got an hour or more of exercise. On average, the kids in the study spent 3.6 hours a day engaged in screen time.
The study couldn't prove cause-and-effect, but the more individual recommendations a child met, the better their ability to think and reason. That's what the researchers found when they compared guideline adherence against performance on brain exercises ("cognition").
"For every additional recommendation met, children had significantly better cognition compared to those who did not meet any of the guidelines," Walsh said.
Kids who met the sleep and screen time guidelines appeared to have the best intellects, followed by the kids who met just the screen time guidelines, the findings showed.
Too much screen time could be wrecking kids' ability to focus, especially if they are switching between apps on a device or between different screens at the same time, Walsh suggested.
"One leading hypothesis is that a lot of time on screens is spent multitasking, using multiple apps or devices at once," Walsh said. "This can interfere with a child's ability to focus and sustain interest on a task. It can be impairing the building blocks for good cognition."
Sleep also is incredibly important to brain development, since that's when the brain reorganizes itself and grows, Walsh added. Exercise has been shown to increase blood flow to the brain and oxygenation of brain tissues, and increases the connectivity of networks in the brain.
Too much screen time could lead to a "cascade" effect where kids don't get enough sleep and then are less active during the day.
"You can see how this collectively would have an impact on brain health," Walsh said.
The findings were published online Sept. 26 in The Lancet: Child & Adolescent Health journal.
According to Dr. Shawna Newman, an attending psychiatrist at Lenox Hill Hospital in New York City, the study "clearly demonstrates the specific benefit of exercise for children, in addition to that of good sleep hygiene and the limitation of screen time contributing positively to cognitive development." Newman was not involved with the new study.
"The article provides an understanding of how vital exercise is to pediatric brain development, and the potentially detrimental effects of reduced sleep and increased screen time for cognition," Newman said.
What should parents do? Walsh advised setting firm rules regarding the use of screens, including how long children are using the screens, the kinds of apps they are using and how many screens they are using at once.
Concerned parents also should preview games or apps before letting their child play, seek out more interactive options that engage the child's mind, and use parental controls to block or filter content and limit screen time.