Changes in the Incidence of Childhood Obesity

Abstract

Objectives: Examine childhood obesity incidence across recent cohorts.

Methods: We examined obesity incidence and prevalence across 2 cohorts of children in the United States 12 years apart using the Early Childhood Longitudinal Studies, parallel data sets following the kindergarten cohorts of 1998 and 2010 with direct anthropometric measurements at multiple time points through fifth grade in 2004 and 2016, respectively. We investigated annualized incidence rate and cumulative incidence proportion of obesity (BMI z-score ≥95th percentile based on Centers for Disease Control and Prevention weight-for-age z-scores).

Results: Among children who did not have obesity at kindergarten entry, there was a 4.5% relative increase in cumulative incidence of new obesity cases by end of fifth grade across cohorts (15.5% [14.1%-16.9%] vs 16.2% [15.0%-17.3%]), though annual incidence did not change substantially. The risk of incident obesity for children who had normal BMI at kindergarten entry stayed the same, but the risk of incident obesity among overweight kindergartners increased slightly. Social disparities in obesity incidence expanded: incidence of new cases during primary school among non-Hispanic Black children increased by 29% (95% confidence interval, 25%-34%), whereas risk for other race-ethnic groups plateaued or decreased. Children from the most socioeconomically disadvantaged households experienced 15% higher cumulative incidence across primary school in 2010 than 1998.

Conclusions: Incidence of childhood obesity was higher, occurred at younger ages, and was more severe than 12 years previous; thus, more youths may now be at risk for health consequences associated with early onset of obesity.

FIGURE 1

Prevalence of obesity between kindergarten and fifth grade for the 1998 and 2010 kindergarten cohorts. Notes: Prevalence of obesity is shown for the cohorts of US children who entered kindergarten in 1998 and in 2010, followed yearly until the end of fifth grade. Whiskers indicate 95% confidence intervals. Data: Early Childhood Longitudinal Study–Kindergarten cohorts of 1998 and 2010.

FIGURE 2

Annualized incidence of obesity between kindergarten and fifth grade for the 1998 and 2010 kindergarten cohorts. Notes: Annualized incidence of obesity is calculated using balanced measurement waves, with person–years at risk in the 2010 cohort calculated after excluding the spring second-grade, fall third-grade, and spring fourth-grade waves, for which no parallel measure was taken in the 1998 cohort. Children with obesity at any previous wave were excluded from calculations for subsequent waves because they were not eligible for incident obesity. Whiskers indicate 95% confidence intervals. Data: Early Childhood Longitudinal Study–Kindergarten Cohorts of 1998 and 2010.