Recommendations made by the “Canadian 24-Hour Movement Guidelines for Children and Youth” for kids between the ages of 8 and 11 years, say that their day should include at least 60 minutes of physical activity, two hours or less of recreational screen time, and 9 to 11 hours of sleep. Yet, in a new study published in The Lancet Child & Adolescent Health, only one in 20 US children met all three of these recommendations. Childhood and adolescence are crucial periods for brain development and behaviour, during a typical 24-hour period, contributes to cognitive performance. Limiting children’s recreational screen time to less than two hours a day, ensuring sufficient sleep and physical activity has now been linked to better development of children’s cognitive abilities.
The study used data from the Adolescent Brain Cognitive Development (ABCD) study of more than 4,500 children between the ages of 8 and 11 years from 21 study sites across the US. Researchers compared daily exercise, technology use and sleeping habits, to the established Canadian Guidelines. The participants’ ‘global cognition’ was then assessed using the standards developed by the National Institute of Health. The results indicate that US children engaged in an average of 3.6 hours a day recreational screen time.
Authors of the new study say that adhering to the guidelines during childhood and adolescence, particularly for screen time, is vital for cognitive development. “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,” says Dr Jeremy Walsh of CHEO Research Institute (Ottawa, Canada). “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. The link between sedentary behaviours, like recreational screen time, is unclear as this research is in the early stages and it appears to vary depending on the types of screen-based activity.”
Children and their parents completed questionnaires and measures at the outset of the trial to estimate the child’s physical activity, sleep and screen time. Children were also asked to complete a cognition test which assessed language abilities, episodic memory, executive function, attention, working memory and processing speed. Researchers used household income, parental and child education, ethnicity, pubertal development, body mass index and whether the child had had a traumatic brain injury, as controls in the study.
The research found that only 5% of children met all three recommendations while 29% met none of those guidelines. Additionally, 63% spent more than two hours a day glued to screens, going over the recommended screen time limit; 82% failed to meet the guidelines for daily physical activity; and 49% did not get the recommended hours of sleep.
The researchers were able to prove that the more recommendations the child met, the better was their cognition. Furthermore, meeting only the screen time guideline or both, the screen time and sleep guidelines, had the strongest associations with cognitive development. The study conclusively showed that of the three guidelines, the screen time recommendation seemed to correlate most strongly with superior cognition: as long as children meet the screen time recommendation, they outscored others in global cognition tests.
Although there is substantial evidence for the association between physical activity and cognitive development, in this particular study, there is no association with cognition. The authors have admitted this as surprising and have suggested that the measure used may not have been specific enough. They were clear that physical activity remains the most important behaviour for physical health outcomes and there is no clear indication that it negatively affects cognition.
Dr Walsh said, “We found that more than two hours of recreational screen time in children was associated with poorer cognitive development. More research into the links between screen time and cognition is now needed, including studying the effect of different types of screen time, whether content is educational or entertainment, and whether it requires focus or involves multitasking. Based on our findings, paediatricians, parents, educators and policymakers should promote limiting recreational screen time and prioritising healthy sleep routines throughout childhood and adolescence.”
The authors have also pointed out some limitations in the study, namely, that it shows an association between reduced screen time and children’s cognitive skills, but does not effectively establish a causal link. As the study is strictly observational, it is not able to establish the underlying cause or the direction of the association. Furthermore, the data is also self-reported and could be subject to bias. The questionnaires were only used at the outset of the study and, hence, are not able to track behavioural change over time. The researchers agreed that future cycles of the study will need to be analysed to understand trends over time.