New research from the CHILD Cohort Study has found that kids who have shorter nighttime sleeps and who spend more time on screens at three years of age are more likely to be overweight or obese by age of five.
The study, published in Nature and Science of Sleep, analyzed data from 2,185 CHILD participants. It found that three-year-olds who spent more than one hour per day on screens were 41% more likely to be overweight or obese by age five, while those who slept less than 10.5 hours per night were 46% more at risk for these conditions. The risk increased when short sleeps were coupled with a bedtime later than 9 pm, and it doubled for those children with short nighttime sleeps who also spent more than one hour per day on screens.
NOCTURNAL SLEEP, NOT NAPS
The research also found that taking naps during the day may not make up for a shorter nighttime sleep in this age group, and that bedtime as a stand-alone risk factor seems only impactful among girls: a bedtime after 9 PM increased the risk of overweight and obesity by 83% in girls only.
“In the last two decades, overweight and obesity have become increasingly common among preschoolers, with over 40 million children currently effected,” observes first author Myrtha E Reyna-Vargas, an M.Sc. and a biostatistician at The Hospital for Sick Children.
“Past studies have found an association between shorter sleep duration and higher BMI, but we wanted to look at it longitudinally–across time–and to see if bedtime and screen time were also influential factors.”
Sleep and screen time information were obtained through parent reported questionnaires. Parents detailed the child’s usual bedtime, wake time, and naptime on weekdays.
The children were classified into three categories of nighttime sleep duration (10.5 hours or less, 10.5–11 hours, and more than 11 hours), and also by bedtime (early being up to 9 PM, and late being after 9 PM). Screen time was reported by parents as the average hours per day spent on all electronic devices (TV/DVDs, computer/tablet, cell phones, video games) at age three and five years. Following Canadian guidelines for preschool children, daily screen time over one hour per day was categorized as excessive.
The analyses were adjusted for variables known to be associated with BMI and sleep in children, including: sex, birth weight, maternal education level, postnatal maternal BMI, breastfeeding status at six months, maternal stress, daily caloric intake and organized physical activity at five years of age.
Dr. Indra Narang, a Senior Associate Scientist at the Hospital for Sick Children and Professor at the University of Toronto, and Dr. Piush Mandhane, Associate Professor at the University of Alberta and CHILD’s Edmonton site leader, were co-senior authors on the paper.
LIMIT SCREEN TIME & GET ENOUGH NIGHTTIME SLEEP
“This study highlights the importance of adequate nocturnal sleep time and moderate screen time to reduce the risk of overweight and obesity in preschool children,” comment the authors. “Given that we can change sleep and screen habits, to reduce children’s risk of developing these conditions further education and targeted interventions are clearly needed to help parents ensure their kids are limiting their screen time and getting enough sleep at night.”