ISU study finds how physical inactivity, screen time contribute to overweight kids

AMES, Iowa -- The American Academy of Pediatrics (AAP) recommends limiting children's total media screen time (including TV, videos and video games) to no more than two hours of quality programming per day. It also recommends boys take 13,000 pedometer steps per day and girls 11,000 in a policy statement on physical activity and childhood obesity. And according to a recent Iowa State University study, parents should heed both those guidelines when it comes to the health of their kids.

The study of 709 children (318 boys, 391 girls) between the ages of 7-12 from 10 elementary schools in Cedar Rapids, Iowa, and Lakeville, Minn., found that children not meeting either the AAP physical activity or screen time recommendations were three to four times more likely to be overweight than those complying with both. It is the first study to show the combined influence of physical activity and screen time on the risk of a child being overweight.

The study also found that relatively few children comply with the AAP recommendations for physical activity. Almost 50 percent of the boys and just over 33 percent of the girls failed to comply with either standard.

"Everybody knows physical activity and screen time are risk factors for healthy development. Those are the two of the big ones that people talk about," said Kelly Laurson, an Iowa State graduate student in kinesiology and lead researcher on the study. "But parents want to know, 'Well how much physical activity? How much screen time is too much?' This study helps to answer these questions."

Joining Laurson on the research team were Gregory Welk, an ISU associate professor of kinesiology; Douglas Gentile, an ISU assistant professor of psychology; Joey Eisenmann, a former ISU professor who is now an assistant professor of kinesiology at Michigan State University; Eric Wickel, assistant professor of athletic training at the University of Tulsa; and David Walsh, president and founder of the National Institute on Media and the Family (NIMF). They produced a paper titled "Combined Influence of Physical Activity and Screen Time: Recommendations on Childhood Overweight," which was published in the current issue of The Journal of Pediatrics.

The study was conducted as part of an obesity prevention program known as SWITCH, designed by the National Institute on Media and the Family. According to Gentile, who is also the director of research for the NIMF, the $1.2 million program was designed to increase children's physical activity, decrease screen time and increase fruit and vegetable consumption.

School nurses measured children's body masses. Average screen time was assessed by surveys, and children wore pedometers to record the number of steps they took each day over a seven-day period to determine their physical activity.

Using students' Body Mass Index to determine their rate of being overweight, the results found that boys who met neither recommended AAP standard for physical activity or screen time were 4.39 times more likely to be overweight than those who followed the standards, and three times more likely among girls. Approximately 10 percent of boys and 20 percent of girls who met both guidelines were overweight among all subjects. By comparison, 35 to 40 percent of the children who did not meet either recommendation were overweight.

"People often want to know what matters for children's health -- is it activity or screen time? The answer is that both matters," Gentile said. "Children's likelihood of being overweight goes up about 50 percent if they spend more than two hours a day in front of electronic screens, about 150 percent if they don't get enough exercise, and about 350 percent if they have both of these problems."

"This demonstrates the power that combined risk factors have on childhood obesity," Laurson said. "This is the most interesting aspect of the study because a lot of parents think, 'Oh my kid's physically active and I don't have to worry about the TV part.' But they still should."

Laurson says that because the study is cross-sectional, it remains unclear whether children are overweight because they do not meet the guidelines, or vice-versa.

"Hopefully, in the future, we can use the longitudinal data to tease out that relationship," he said. "However, the study does show the independent association with childhood overweight and identifies the utility of the AAP recommendations, and how many children are meeting, or not meeting, them."

Gentile and Welk have received a grant to continue the NIMF research in Cedar Rapids and extend it to additional communities in Iowa. Gentile expects to be publishing research papers related to other aspects of that study in coming months.