Children who spend less than 2 hours a day engaging in recreational screen-based activities, such as using social media on the Internet and watching television, and who get sufficient sleep and engage more in physical activities have better cognition than children who spend more time engaging in screen-based activities and who get less sleep and engage less in physical activity, new research suggests.

Investigators used data from a 10-year study of more than 4500 children aged 8 to 11 years to assess adherence to Canadian 24-hour Movement Guidelines for Children and Youth regarding physical activity, recreational screen time, and sleep duration.

They found that adherence to all three recommendations was associated with superior global cognition. Moreover, adherence to screen time recommendations alone, as well as screen time and sleep recommendations together, were also was associated with better cognition. Physical activity was associated with improved physical health.

Only half of participants met sleep recommendations, only one third met screen time recommendations, and fewer than one fifth met physical activity recommendations. Only 5% of children met all three recommendations.

“We found that the whole day matters for cognitive health,” said study author Joel Barnes, MSc, knowledge and data analyst, Healthy Active Living and Obesity Research Group, Children’s Hospital of Eastern Ontario Research Institute, Ottawa, Canada.

“Eight- to 10-year-olds in the US who met 24-hour Movement Behavior Guidelines had superior global cognition scores, compared to children who did not meet these recommendations, with each additional recommendation met being associated with superior global cognition,” Barnes added.

“These findings are the result of taking an integrative approach, looking at children’s movement behaviors across the entire day, which allows us to consider the entire movement behavior continuum,” he told Medscape Medical News.

The study was published online September 26 Lancet Child and Adolescent Health.

Ubiquitous in Modern Life

“Physical activity, sedentary behavior, and sleep might independently and collectively affect cognition,” the authors write.

“Good sleep quality and quantity are positively associated with cognition and academic performance in children and adolescents,” they write.

Some early studies have suggested negative associations between sedentary behaviors and cognition in children, although the findings are inconsistent, the authors note, possibly because of diversity in the types of sedentary behavior studied.

However, with the “widespread use of screen-based devices, their use takes up much of children’s sedentary time,” they write.

The 2016 Canadian 24-Hour Movement Guidelines for children aged 5 to 13 years recommend ≥60 minutes of physical activity of moderate to vigorous intensity, ≤2 hours of recreational screen time per day, and 9 to 11 hours of uninterrupted sleep per night.

The 24-Hour Movement Behavior Guidelines were developed as a marker for optimal physical health in children, Barnes said.

“We have found previously that the more guidelines met by children and youth, the better their physical health, but we had not had a chance to study the association between these movement behaviors and cognition,” he said.

“We know that physical activity has a strong, positive effect on brain health in children, while physical inactivity — insufficient physical activity — and sedentary behavior may have a negative impact, but much more research is needed, and, importantly, this was not the focus of our study,” Barnes noted. “Rather, we were interested specifically in the relationship between screen time and cognition, because screens are ubiquitous in modern life, and children and youth growing up today live in a context where screens are a regular part of their life.”

“The ABCD [Adolescent Brain Cognitive Development] study provided an opportunity for us to look at cognition across the day, and the pattern we have seen with physical health seems to be similar for cognition — the whole day matters,” he said.

The ABCD study is a 21-site US-based longitudinal, observational study that tracks children through adolescence across numerous domains related to brain development and health. Data are being collected every 1 to 2 years over a 10-year period.

For this analysis, the investigators used baseline cross-sectional data from the annual curated release 1.0 from the ABCD study that began on September 1, 2016.

The primary outcome relevant to the current study was global cognition, assessed with the NIH Toolbox, consisting of seven validated and reliable psychometric tasks spanning six cognitive domains: language abilities, episodic memory, executive function, working memory, and processing speed.

The researchers assessed global cognition with these subcomponent composites because of the “multiplicity of independent and probably convergent influences of the behaviors assessed in the ABCD study on multiple domains of cognition.”

Exposures of interest were physical activity (the number of days the participant was physically active for ≥60 minutes during the previous 7 days); screen time (the number of hours spent per typical weekend and weekday performing recreational screen-based activities); and sleep duration (the number of hours of sleep the child got on most nights).

The researchers assessed covariates with established positive associations with global cognition: high household income, parental and child education, being of Asian or white descent, and being in advanced stage of pubertal development. They also assessed covariates known to be negatively associated with global cognition, including high body mass index and incidence of traumatic brain injury.

The Whole Day Matters

The first annual curated release of the ABCD dataset included 4524 children aged 8 to 11 years. Of those, 836 to 853 participants were excluded from the regression analysis, owing to incomplete data.

Participants reported being physically active for ≥60 minutes on a mean of 3.7 (SD, 2.3) days per week.

The mean recreational screen time was 3.6 (SD, 2.9) hours per day, and the mean sleep duration was 9.1 (SD, 1.1) hours per night.

A mean of 1.1 (SD, 0.9) guideline recommendations were met.

Overall, 2303 (51%), 1655 (37%), and 793 (18%) participants met the sleep, screen time, and physical activity recommendations, respectively; 3190 (71%) participants met one or more recommendations, and 216 (5%) met all three recommendations.

Eighteen percent of the children were obese.

There was a positive association between global cognition and each additional recommendation met (β = 1.44; 95% confidence interval [CI], 0.82 – 2.07; P < .0001).

If all three recommendations, as opposed to no recommendations, were met, global cognition was also superior (β = 3.89; 95% CI, 1.43 – 6.34; P = .0019).

Compared with no recommendations being met, meeting only the screen time recommendation or both the screen time and the sleep recommendations together also had positive associations with global cognition (β = 4.25; 95% CI, 2.50 – 6.01; P < .001; and β = 5.15; 95% CI, 3.56 – 6.74; P < .001, respectively).

These models accounted for 21.8% to 22.8% of the overall variance in global cognition. Meeting other combinations of recommendations was not associated with global cognition.

“Not much is known about the potential mechanisms explaining the relationship between screen time and cognition, which is an important area of future research,” Barnes commented.

However, what this study suggests is that the “whole day matters for cognitive health, with every additional movement behavior recommendation met associated with benefits to global cognition,” he noted.

Canary in a Coal Mine

Commenting on the study for Medscape Medical News, Eduardo Esteban Bustamante, PhD, assistant professor, Department of Kinesiology and Nutrition, University of Illinois at Chicago and College of Applied Sciences, Chicago, who was not involved with the study, called it “fascinating.”

He noted that most studies have investigated each component separately, but it was “clever how they [the investigators] looked at whether kids were meeting the combination of guidelines and how that influenced cognition.”

He cautioned that because the study was cross-sectional, it was “just a snapshot” and that association does not equate with causality.

“Maybe kids with lower cognition are more drawn to video and TV, or maybe some third factor is causing these things — for example, maybe households with less structure allow kids more screen time,” suggested Bustamante, who is the author of an accompanying editorial.

Nevertheless, this study may be “a canary in a coal mine, so we need to figure out and research further whether screen time is uniquely important,” he said.

An additional avenue of investigation is whether the particular type of screen activity matters, he said. “The literature is pretty equivocal, with different findings, depending on what the children are engaged in during screen time — for example, kids who watch Sesame Street have been shown to do better at school.”

Barnes added, “We need to consider our screen habits and screen use as well as the rules and restrictions that we apply to the recreational time of children and youth, because getting no more than 2 hours of screen time per day — independent of screen content — is beneficial to cognition.”

The study was funded by the National Institutes of Health (NIH) and used data from the NIH-funded ABCD study. It was conducted by researchers from CHEO Research Institute, University of Ottawa, and Carleton University. Dr Barnes and coauthors and Dr Bustamante have disclosed no relevant financial relationships.

Lancet Child Adolesc Health. Published online September 26, 2018. AbstractEditorial

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