Children aged eight to 11 who used screens for fun for less than two hours a day performed better in tests of mental ability, a study found. Combining this with nine to 11 hours of sleep a night was found to be best for performance.
Researchers said more work was now needed to better understand the effects of different types of screen use. However, they acknowledge that their observational study shows only an association between screen time and cognition and cannot prove a causal link. And it did not look at how children were using their screen time, be it to watch television, play videogames or use social media.
The study of 4,500 US children used questionnaires to estimate the child's: physical activity; sleep; and recreational screen time. Children also completed a test, which assessed cognitive skills, including: language; memory; and attention. The study controlled for: household income; parental and child education; ethnicity; pubertal development; body mass index (BMI); and traumatic brain injury.
It found that children who each day had less than two hours of recreational screen time, got nine to 11 hours of sleep, and did at least one hour of physical activity performed better than who did none of these. Less than two hours of screen time a day was the one factor most linked to better performance in the test.
Dr Jeremy Walsh, from the CHEO Research Institute, in Ottawa, Canada, said: "Based on our findings, paediatricians, parents, educators, and policymakers should promote limiting recreational screen time and prioritising healthy sleep routines throughout childhood and adolescence." Walsh added that more research was now needed into the links between screen time and cognition, including studying the effects of different types of screen time.
He said there was some evidence, for example, that video games and educational TV programmes might have cognitive benefits. In contrast, emerging evidence suggested the use of mobile devices and social media may be harmful for attention, memory and impulse control, he said.
However, the authors acknowledged there were limitations to their study, including that the data was self-reported. The questionnaires were also only used only at the beginning of the study and so did not track how behaviours may change over time.
Dr Kirsten Corder, senior investigator scientist at the University of Cambridge, who was not involved in the study, said it added to existing evidence showing potential negative links with screen time and cognitive development in children. But she pointed out that the children may have struggled to answer the questions accurately. Corder also said further work was needed to develop more accurate ways to assess the effects of screen time in detail. "These results will hopefully stimulate further research using techniques that allow researchers to explore how multiple behaviours may interplay to benefit cognition and health," she said.
Background: Childhood and adolescence are crucial periods for brain development, and the behaviours during a typical 24 h period contribute to cognitive performance. The Canadian 24-Hour Movement Guidelines for Children and Youth recommend at least 60 min physical activity per day, 2 h or less recreational screen time per day, and 9–11 h sleep per night in children aged 8–11 years. We investigated the relationship between adherence to these recommendations and global cognition.
Methods: In this cross-sectional observational study, we obtained data from the first annual curated release of the Adolescent Brain Cognitive Development study, a 10-year longitudinal, observational study. Data were collected from 21 study sites across the USA between Sept 1, 2016, and Sept 15, 2017. The participants were 4524 US children aged 8–11 years from 20 study sites. Exposures of interest were adherence to the physical activity, recreational screen time, and sleep duration guideline recommendations. The primary outcome was global cognition, assessed with the NIH Toolbox (National Institutes of Health, Bethesda, MD, USA), which we analysed with multivariable linear mixed-effects models to examine the relations with movement behaviour variables.
Findings: Complete movement behaviour data were available for 4520 participants. The mean number of guideline recommendations met was 1·1 (SD 0·9). Overall, 2303 (51%) participants met the sleep recommendation, 1655 (37%) met screen time, and 793 (18%) met the physical activity recommendation. 3190 (71%) participants met at least one recommendation, whereas 216 (5%) of participants met all three recommendations. Global cognition was positively associated with each additional recommendation met (β=1·44, 95% CI 0·82–2·07, p<0·0001). Compared with meeting none of the recommendations, associations with superior global cognition were found in participants who met all three recommendations (β=3·89, 95% CI 1·43 to 6·34, p=0·0019), the screen time recommendation only (β=4·25, 2·50–6·01, p<0·0001), and both the screen time and the sleep recommendations (β=5·15, 3·56–6·74, p<0·0001).
Interpretation: Meeting the 24 h movement recommendations was associated with superior global cognition. These findings highlight the importance of limiting recreational screen time and encouraging healthy sleep to improve cognition in children.
Jeremy J Walsh, Joel D Barnes, Jameason D Cameron, Gary S Goldfield, Jean-Philippe Chaput, Katie E Gunnell, Andrée-Anne Ledoux, Roger L Zemek, Mark S Tremblay
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[link url="https://www.thelancet.com/journals/lanchi/article/PIIS2352-4642(18)30278-5/fulltext"]The Lancet Child & Adolescent Health Journal article summary[/link]