Each child was also tested for cognitive skills, such as language, memory and attention.
After controlling for ethnicity, income, parental and child education, puberty, body mass index and traumatic brain injury, the researchers found that children who spent less than two hours of their free time on screens, slept for nine to 11 hours per night and had at least one hour of physical activity per night performed better than those who didn’t fall into any of those specifics.
But of all factors examined, they noticed that children with less than two hours of screen time per day yielded the best results, yet only one in 20 U.S. children in the study met the Canadian 24-Hour Movement Guidelines for Children and Youth’s screen time, physical activity and sleep recommendations. On average, U.S. children spend approximately 3.6 hours per day engaged in recreational screen time, the researchers found.
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Overall, 51 percent of the participants met the sleep recommendation (9-11 hours per night), 37 percent met the screen time recommendation (less than two hours) and 18 percent met the physical activity recommendation. (one hour). Approximately 71 percent of participants met at least one recommendation, but only 5 percent met all three recommendations.
With more recommendations met, global cognition increased. Still, researchers reiterated, “meeting only the screen time recommendation or both the screen time and sleep recommendations had the strongest associations with cognitive development.”
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"Behaviours and day-to-day activities contribute to brain and cognitive development in children, and physical activity, sedentary behaviour, and sleep might independently and collectively affect cognition," study author Jeremy Walsh said in a statement. "Evidence suggests that good sleep and physical activity are associated with improved academic performance, while physical activity is also linked to better reaction time, attention, memory, and inhibition."
Walsh and his team said they hope pediatricians, educators, lawmakers and parents will read the study and promote limiting recreational screen time and healthy sleep schedules.
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But “more research into the links between screen time and cognition is now needed,” Walsh added, “including studying the effect of different types of screen time, whether content is educational or entertainment, and whether it requires focus or involves multitasking.”
The researchers also noted that because this was an observational study, they can’t establish underlying causes or the direction of the association.
Read the full study at thelancet.com.