Incidence of Childhood Obesity in the United States

Study Questions:

What is the national incidence of obesity among elementary school children?


Data from the Early Childhood Longitudinal Study, a representative prospective cohort of 7,738 participants who were in kindergarten in 1998 in the United States, were used for the present analysis. Weight and height were measured seven times between 1998 and 2007. Of the 7,738 participants, 6,807 were not obese at baseline; these participants were followed for 50,396 person-years. The 2000 Centers for Disease Control and Prevention (CDC) Growth Charts were used to calculate each child’s body mass index (BMI), standardized to the reference population for the child’s age and sex. Annual incidence of obesity, the cumulative incidence over 9 years, and the incidence density (cases per person-years) overall were estimated. In addition, estimates were examined by sex, socioeconomic status, race/ethnic group, birth weight, and kindergarten weight.


For children entering kindergarten with mean age of 5.6 years, 12.4% were obese and an additional 14.9% were overweight. In eighth grade with a mean age of 14.1 years, 20.8% were obese and an additional 17.0% were overweight. The annual incidence of obesity decreased from 5.4% during kindergarten to 1.7% between fifth and eighth grade. Overweight 5-year-olds were four times as likely as normal-weight children to become obese (9-year cumulative incidence, 31.8% vs. 7.9%), with rates of 91.5 versus 17.2 per 1,000 person-years. Among children who became obese between the ages of 5 and 14 years, nearly one-half had been overweight and 75% had been above the 70th percentile for BMI at baseline. The prevalence of obesity was higher among Hispanic children than among non-Hispanic white children at all ages. Starting in third grade, non-Hispanic black children also had a significantly higher prevalence of obesity than non-Hispanic white children. Among all children during the follow-up period, the greatest increase in the prevalence of obesity was between first and third grades, when the prevalence increased from 13.0% to 18.6%. At all ages, the prevalence of obesity was highest among children in the next-to-poorest quintile, reaching 25.8% by eighth grade.


The investigators concluded that incident obesity between the ages of 5 and 14 years was more likely to have occurred at younger ages, primarily among children who had entered kindergarten overweight.


These data demonstrate the increased likelihood that children who enter elementary school with higher BMI are much more likely to be obese at older ages. This suggests the importance of both school-based and community-based interventions to reduce incidence of overweight and obesity among young children and identify factors associated with obesity among younger children.

Clinical Topics: Congenital Heart Disease and Pediatric Cardiology, Diabetes and Cardiometabolic Disease, CHD and Pediatrics and Prevention, CHD and Pediatrics and Quality Improvement

Keywords: Birth Weight, Follow-Up Studies, Overweight, European Continental Ancestry Group, Pediatric Obesity, Hispanic Americans, Child, Preschool, Incidence, Prevalence, Body Mass Index, Cardiovascular Diseases, Growth Charts, United States

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