Incidence of Childhood Obesity in the United States

Although the increased prevalence of childhood obesity in the United States has been documented, little is known about its incidence. We report here on the national incidence of obesity among elementary-school children.

We evaluated data from the Early Childhood Longitudinal Study, Kindergarten Class of 1998-1999, a representative prospective cohort of 7738 participants who were in kindergarten in 1998 in the United States. Weight and height were measured seven times between 1998 and 2007. Of the 7738 participants, 6807 were not obese at baseline; these participants were followed for 50,396 person-years. We used standard thresholds from the Centers for Disease Control and Prevention to define "overweight" and "obese" categories. We estimated the annual incidence of obesity, the cumulative incidence over 9 years, and the incidence density (cases per person-years) overall and according to sex, socioeconomic status, race or ethnic group, birth weight, and kindergarten weight.