Wonwoo Byun, Ph.D., is an Assistant Professor in the Department of Health, Nutrition, and Exercise Sciences, and a core faculty in the Master of Public Health Program at North Dakota State University. His research focus includes physical activity and sedentary behavior in children. He is particularly interested in developing interventions that promote physical activity and reduce sedentary behavior for childhood obesity prevention.
What is the data saying about childhood obesity?
If you are a subscriber of The New York Times, you might have read an article with the headline of “Obesity Rate for Young Children Plummets 43% in a Decade.”1 This dramatic claim was based on data from the National Center for Health Statistics (published in the Journal of American Medical Association in 2014), which states that 8.4% of American preschool-age-children were obese in 2012 compared to 13.9% in 2003. As a childhood obesity researcher, and more importantly a parent of a 4-year-old child, I was very excited to see this promising news from The New York Times, one of the most widely read newspapers in the United States. However, after reading the original report in The Journal of the American Medical Association,2 I see that their conclusion is that even if the obesity rate among very young children (2 to 5 years old) decreased, the overall prevalence of obesity for youth in general has not experienced significant change since 2003. In fact, childhood obesity rates have been more than doubled during the past 30 years and one in every five American children (2 – 19 years) is currently obese, suggesting that the current generation of American children is heavier than ever before.
Why is childhood obesity one of the most pressing public health concerns?
In adults, obesity is a leading risk factor for many chronic diseases, including type 2 diabetes. In fact, obese individuals have about triple the risk of type 2 diabetes as compared to their normal weight counterparts. This strong link between obesity and type 2 diabetes also exists in children; in fact, over 95% of children diagnosed with type 2 diabetes were either overweight or obese.3 Given the evidence that obese children are more likely to become obese adults who generally have poor health, we need to make a focused effort to prevent obesity during the childhood.
What is sedentary behavior?
Although there is a strong genetic influence on childhood obesity, sedentary behavior can play a significant role in childhood obesity. Although sedentary behavior sounds self-explanatory, it is a complex of behaviors that manifest differently under diverse environments. The term “sedentary” originated in the late 16th century from Latin word “sedentārius,” and is characterized by sitting. Unlike the encyclopedic definition, researchers and health professionals characterize sedentary behavior as any waking activity that does not require energy expenditure significantly above a resting level. In general, the key characteristic of sedentary behavior is sitting or reclining posture (i.e., lying down); thus common sedentary behaviors include TV viewing, computer use, video game playing, riding cars, and reading.
How is sedentary behavior different from lack of physical activity?
Despite this clear definition, there is a common misconception about sedentary behavior when we talk about sedentary behavior and low physical activity in children. Authoritative public health organizations, the American Academy of Pediatrics and the Institute of Medicine, recommend children to engage in no more than 2 hours of sedentary behavior and at least 1 hour of moderate-to-vigorous intensity physical activity on a typical day. However, consider an 8-year-old girl who is awake for 14 hours, and who sleeps 10 hours on a typical day. Although this 8-year-old girl can meet the recommended level of physical activity by engaging in 1 – 1.5 hours of soccer practice every day, she could easily spend more than 2 hours in sedentary behavior by watching TV, riding in the car to school and soccer practice, and doing homework using a computer. This clearly suggests that children can be highly sedentary even when they meet the recommended levels of physical activity.
How much time do children spend in sedentary behavior?
Using highly accurate physical activity monitors, a nation-wide study quantified the amount of time spent in sedentary behavior by American children.4 On average, children age 12 and older spent over 55% of their waking hours (> 7.5 hours/day) in sedentary behavior. It was also reported that at least 49% of children age 6-11 and 56% of children age 12-15 years watched more than two hours of TV on a typical day.5
More astonishing data was reported for very young American children while attending preschool. Parents or caregivers typically believe that preschool-age-children are always physically active. However, it was discovered that 3 - 5 year-old boys and girls spent over 80% of their time in sedentary behavior while attending preschools. More interestingly, caregivers believed that the preschool-age-children were sufficiently active and that the children needed to learn to sit for primary school preparation.
Why do we care about children’s sedentary behavior?
In children, accumulating evidence shows that more sedentary behavior increases the risk of obesity and type 2 diabetes. Children who watched more than 2 hours of TV per day were 2.6 times more likely to be overweight compared to those who watched less than 2 hours of TV per day.6 More importantly, data from more recent studies confirmed that detrimental effect of excessive sedentary behavior on obesity and type 2 diabetes is independent of children’s physical activity and dietary intake. In other words, too much time in sedentary behavior (i.e., watching TV, playing video games) increases the risk of obesity and type 2 diabetes regardless of how much soccer children play and or how little chocolate milk children drink.
What can we do to reduce sedentary behavior in children?
Physical activity is fundamental for the healthy development of children. However, technological advances have drastically changed children’s behavior by creating an environment that promotes sedentary behavior. Today, most children in the U.S. sit while being driven to school. In addition, a typical American child will grow up in a household that has three TVs, two DVDs/VCRs, two computers, and two video game consoles. Further, two thirds of U.S. children have their own personal TV, half have a personal video game console, and a third have a personal computer with internet access in their bedroom. As discussed earlier, excessive sedentary behavior impacts children’s both short-term and long-term health. Therefore, collaborative efforts to promote physical activity and reduce sedentary behavior by parents, schools, and health professionals are imperative, and the importance of those efforts cannot be overemphasized.
1. Times TNY. Obesity Rate for Young Children Plummets 43% in a Decade. 2014.
2. Ogden CL, Carroll MD, Kit BK, Flegal KM. Prevalence of childhood and adult obesity in the United States, 2011-2012. Jama. Feb 26 2014;311(8):806-814.
3. Haines L, Wan KC, Lynn R, Barrett TG, Shield JP. Rising incidence of type 2 diabetes in children in the U.K. Diabetes care. May 2007;30(5):1097-1101.
4. Matthews CE, Chen KY, Freedson PS, et al. Amount of time spent in sedentary behaviors in the United States, 2003-2004. American journal of epidemiology. Apr 1 2008;167(7):875-881.
5. Sisson SB, Church TS, Martin CK, et al. Profiles of sedentary behavior in children and adolescents: the US National Health and Nutrition Examination Survey, 2001-2006. International journal of pediatric obesity : IJPO : an official journal of the International Association for the Study of Obesity. 2009;4(4):353-359.
6. Lumeng JC, Rahnama S, Appugliese D, Kaciroti N, Bradley RH. Television exposure and overweight risk in preschoolers. Archives of pediatrics & adolescent medicine. Apr 2006;160(4):417-422.