Screens — on computers, smartphones, tablets and more — surround us more than ever. But it might be best to look away. Nearly two out of three U.S. kids spend more than two hours a day looking at screens, a new study finds. The kids who spend more time staring at screens perform worse on memory, language and thinking tests than do those who spend less time in front of a device. That’s the result of a study of more than 4,500 kids 8- to 11-years old.
Time on devices has its pros and cons. Screen time before bed can make it harder to sleep. But some time with devices also can improve a student’s moods. For this study, researchers wanted to find out how much time kids were spending on screens — whether a smartphone, a television, an iPad or a computer. They also wanted to look at how much sleep and exercise these kids were getting. Finally, the scientists wanted to gauge kids’ cognitive abilities. These are mental activities — such as solving puzzles, remembering things or learning something new.
The researchers used data gathered as part of a large, long-term study. Called the Adolescent Brain Cognitive Development (ABCD) Study, it surveyed more than 4,500 kids and their parents. The study asked about screen time. It also asked about exercise and sleep, and tested memory and learning.
So how much screen time is too much? The researchers went with guidelines from experts. These recommend no more than two hours of recreational screen time a day. They also advise kids to get at least an hour of exercise each day and between nine and 11 hours of sleep at night.
If that prescription seems strict, it was. Only five in every 100 of the surveyed children met all three guidelines. In fact, 29 in every 100 didn’t meet any of the guidelines. So they were “getting less than nine hours of sleep, they’re on their screens for longer than two hours and they’re not being physically active,” notes Jeremy Walsh. He’s an exercise physiologist — someone who studies how bodies work during exercise. He works at the University of British Columbia in Okanagan.
Lots of screens, not so much sleep
On average, children in this study spent 3.6 hours a day using screens for video games, videos and other fun. They also exercised an hour or more fewer than four days a week. At least they slept an average of 9.1 hours a night.
Less screen time was linked with better cognitive scores. Children who spent fewer than two hours on screens scored about four percent higher on thinking-related tests than did kids who spent more time on their screens. Kids who met the recommendations for both screen time and sleep also got better scores on their thinking tests. When analyzed on their own, sleep and physical activity didn’t seem to influence test results. It was screen time that really made a difference.
“This raises a flag,” Walsh says. The new data add to concerns that heavy use of smartphones, tablets or televisions can hurt growing minds. Walsh and his colleagues published their findings online September 26 in Lancet Child & Adolescent Health.
Because the study only asked people about their habits once, it only captures a single snapshot in time. That means that Walsh and his colleagues can’t tell if the amount of screen time kids get actually changes brain development. But, Walsh adds, “Without [knowing] what kids are actually doing with their screens, we’re seeing that the two-hour mark actually seems to be a good recommendation for benefiting cognition.”
The study can’t say whether screen time actually hurt thinking skills. Kids who spend lots of time with devices might miss out on other activities that improve their memory or problem-solving skills. “You don’t know which is the chicken and which is the egg here,” cautions Michael Rich. He is a pediatrician. That’s a doctor who focuses on children. Rich works at Boston Children’s Hospital in Massachusetts. It could be that smarter kids are less likely to spend lots of time on screens, he says. If true, they would get better test scores — but it wouldn’t be because they used devices less.
Simple cause-and-effect relationships often don’t exist in human behavior, Rich says. Instead of broad rules for all kids, “we need to tailor what we learn from science to individual children.”
But by looking at screen, sleep and exercise behaviors in combination, the results offer a fuller look at children’s health. That’s a peek that’s sorely needed, says Eduardo Esteban Bustamante. He’s a kinesiologist — someone who studies how bodies move. He works at the University of Illinois in Chicago. “We don’t know a lot yet about how these behaviors interact with one another to influence kids’ cognitive development,” he says.
The ABCD Study will keep collecting data from these families for another 10 years. This means scientists may be able to learn more about how screen time affects kids through their teen years and beyond. “I’m really excited to see where this line of research goes,” Bustamante says.
adolescent Someone in that transitional stage of physical and psychological development that begins at the onset of puberty, typically between the ages of 11 and 13, and ends with adulthood.
average (in science) A term for the arithmetic mean, which is the sum of a group of numbers that is then divided by the size of the group.
behavior The way something, often a person or other organism, acts towards others, or conducts itself.
cognition The mental processes of thought, remembering, learning information and interpreting those data that the senses send to the brain.
cognitive A term that relates to mental activities, such as thinking, learning, remembering and solving puzzles.
colleague Someone who works with another; a co-worker or team member.
development (in biology) The growth of an organism from conception through adulthood, often undergoing changes in chemistry, size and sometimes even shape.
kinesiologist A scientist who studies how the human body moves and how it can function more efficiently (by putting a minimum of strain on tissues).
pediatrics A field of medicine that has to do with children and especially child health. A doctor who works in this field is known as a pediatrician.
physiologist A scientist who studies the branch of biology that deals with how the bodies of healthy organisms function under normal circumstances.
smartphone A cell (or mobile) phone that can perform a host of functions, including search for information on the internet.
survey (v.) To ask questions that glean data on the opinions, practices (such as dining or sleeping habits), knowledge or skills of a broad range of people. Researchers select the number and types of people questioned in hopes that the answers these individuals give will be representative of others who are their age, belong to the same ethnic group or live in the same region. (n.) The list of questions that will be offered to glean those data.
tablets (in computing) A small, hand-held computer that can connect to the Internet and that users can control using a touch screen. An Apple iPad, Samsung Galaxy and Amazon Kindle Fire are all examples of tablets.
Journal: J. J Walsh et al. Associations between 24 hour movement behaviours and global cognition in US children: a cross-sectional observational study. Lancet Child & Adolescent Health. Published online September 26, 2018. doi: 10.1016/ S2352-4642(18)30278-5.