Both increased activity and less screen time are important for preventing overweight and obesity in adolescents, new research suggests.
Findings from the study of nearly 6000 adolescents aged 10-14 years suggest that if a youth spends more than 8 hours a day in front of a device with a screen, even performing some physical activity might not be enough to reverse the increased risk for overweight and obesity.
And on the flip side, being very sedentary can lead to obesity even without excessive recreational screen time.
“Physical activity isn’t necessarily the opposite of sedentary behavior. You can be both physically active and sedentary…We don’t really know the benefits of physical activity if you spend the rest of your day sitting down or lying down,” lead author Jason M. Nagata, MD, assistant professor of pediatrics at the University of California, San Francisco, told Medscape Medical News.
One conclusion from the study is that at least 12,000 steps and less than 4 hours a day of recreational screen time minimize the risks for overweight and obesity. Although that might not be realistic for many kids, clinicians might consider focusing particular efforts on those with the highest screen time and lowest activity levels, Nagata advised.
“The highest risk group for obesity and other metabolic syndrome features are at the extremes. While in general more activity and less screen time are good, it’s particularly important to avoid really high levels of screen time, like over 8 hours per day, or really low physical activity, like less than 6000 steps…If you want to be very concrete with your patients, at least get them out of these high-risk groups,” he recommended.
The findings were published online in JAMA Network Open.
Filling in the Guideline Gaps: No Previous Evidence on Screen Time
The study was prompted by gaps in current guidelines, say Nagata and colleagues.
The Physical Activity Guidelines Advisory Committee Scientific Report, released in 2018 by the Department of Health & Human Services (HHS) and reported by Medscape Medical News, recommends 60 minutes of moderate to vigorous intensity physical activity per day for adolescents, but it doesn’t make a recommendation about screen time because not enough data had been available.
The American Academy of Pediatrics had previously recommended a limit of no more than 2 hours per day of screen time but dropped that in 2016 in favor of formulating individualized “family media use plans” involving approaches such as establishing screen-free times of the day or zones in the home.
In the last 5 years, the proportion of US adolescents meeting the physical activity guidelines has decreased to below 25%, dropping to less than 10% during the COVID-19 pandemic lockdown period.
At the same time, recreational screen use time has nearly tripled over the past few decades and rose dramatically during the pandemic as well, Nagata and colleagues write.
More Steps, Less Screen Time Equals Healthier Kids
The cross-sectional study was conducted with data from 5797 youth aged 10-14 years participating in the Adolescent Brain Cognitive Development (ABCD) study. They were analyzed between September 10, 2018, and September 29, 2020, overlapping with the COVID-19 pandemic. There were 21 racially and ethnically diverse study sites across the United States; two thirds of participants were White, and the rest were Black, Hispanic, Asian, or American Indian.
Participants, of whom 35% had overweight or obesity, wore Fitbit digital devices that counted their steps. Recreational screen time, including television, movies, videos, video games, texting, and social media, were reported via questionnaires by the youths.
Overall, they reported a mean screen time of 6.5 hours per day and had a mean count of 9247 steps per day over 21 days.
Based on data from prior studies, daily step counts were categorized as low (1000-6000), medium (6001-12,000), or high (> 12,000), and daily screen time was divided into increments of low (< 4 hours), medium (> 4 to 8 hours), and high (> 8 hours).
In models including both screen time and step count, medium and high screen time categories were associated with significantly higher rates of overweight or obesity compared with the low screen time category (risk ratio [RR], 1.24 and 1.29, respectively).
Similarly, low and medium step count categories were associated with significantly higher overweight/obesity risk compared with high step counts (RR, 1.30 and 1.19, respectively).
A sensitivity analysis excluding the COVID-19 pandemic period produced similar findings.
Among those with low screen use, low step count was associated with a 7.48 higher BMI percentile, and medium step count with a 1.55 higher BMI percentile.
However, among those with high screen use, there was an eight- to ninefold increase in BMI percentile regardless of the step count category. Similarly, among those with low step counts, even the lowest screen time increased the BMI percentile by more than 7 points.
“At the extremes, if you have very low activity or very high screen time, the other wouldn’t compensate for that. I thought that was a very interesting finding,” Nagata said.
The HHS physical activity guidelines were first issued in 2008. There was an interim revision in 2013 prior to the 2018 full update.
This study was funded by grants from the American Heart Association, the Doris Duke Charitable Foundation, and the National Institutes of Health. Nagata has reported no relevant financial relationships.
JAMA Netw Open. Published online February 9, 2023. Full text
Miriam E. Tucker is a freelance journalist based in the Washington, DC, area. She is a regular contributor to Medscape, with other work appearing in The Washington Post, NPR’s Shots blog, and Diabetes Forecast magazine. She is on Twitter: @MiriamETucker.
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