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Racial/Ethnic Disparities: a Longitudinal Study of Growth Trajectories Among US Kindergarten Children



While previous studies have documented racial/ethnic disparities in childhood obesity, less is known about when disparities emerge, how they evolve, and the most appropriate early childhood period for targeted interventions. We examined racial/ethnic differences in growth trajectories among US kindergarten-aged children followed from birth and identified sensitive periods at which disparities emerge.

Subjects and Methods

This is a longitudinal study design using Early Childhood Longitudinal Study Birth Cohort data. We employed random effects growth curves to model trajectories of mean BMI z-scores by race/ethnicity and sex. To visualize sensitive periods for emergence of disparities, we used locally estimated smoothing spline curves to graph the relationship between age and BMI z-score within each racial group.


Unweighted baseline sample size included ~ 7200 children. Overall, 54.6% of children were white, 23.1% Hispanic, 15.7% African-American, 3.4% Asian, 2.8% American-Indian, and 0.4% Pacific-Islander. Mean BMI z-scores for Hispanic boys and American-Indian boys and girls were already significantly higher by 24 months than their white peers and remained higher through kindergarten entry. African-American and Asian children started with significantly lower birth-weights compared to whites, but Asian girls’ growth trajectory remained slow, while African-American girls experienced steeper increases in BMI z-scores and ultimately overtook their white and Asian peers over time. By kindergarten entry, disparities were present across all racial/ethnic groups.


Racial/ethnic disparities in US children’s weight status and growth trajectories emerge at different ages for different racial groups, but they are generally well established by kindergarten age. Our findings indicate that interventions designed to prevent early childhood overweight/obesity should be implemented early in the life course.

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Fig. 1
Fig. 2



Body mass index


Early Childhood Longitudinal Study Birth Cohort


National Center for Education and Statistics


Ordinary least squares


Socioeconomic status


Locally estimated smoothing splines


United States


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Author information



Corresponding author

Correspondence to Inyang A. Isong.

Ethics declarations

Conflict of Interest

Drs. Richmond and Kawachi declare no conflict of interest.

Dr. Isong received funding support (stipend) during her doctoral program from the Pritzker obesity prevention award.

Dr. Mauricio Avendaño is supported by the European Union’s Horizon2020 research and innovation programme under grant agreements 633666 (Lifepath) and 667661 (MINDMAP) and the National Institute on Aging (award number R01AG040248).

Research Involving Human Participants and/or Animals

This study involved secondary data analysis, with no direct contact with human participants and/or animals. The study was approved by the NCES and Harvard School of Public Health IRB.

Informed Consent

This study involved secondary data analysis, with no direct contact with human participants and/or animals. We used secondary data from the Early Childhood Longitudinal Study Birth Cohort (ECLS-B) study, sponsored and conducted by the National Center for Education and Statistics (NCES).

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Isong, I.A., Richmond, T., Avendaño, M. et al. Racial/Ethnic Disparities: a Longitudinal Study of Growth Trajectories Among US Kindergarten Children. J. Racial and Ethnic Health Disparities 5, 875–884 (2018).

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  • Racial/ethnic disparities
  • BMI z-score
  • Growth trajectories
  • Obesity
  • ECLS-B