• Inyang A Isong, Tracy Richmond, Mauricio Avendaño, and Ichiro Kawachi.
• Boston Children's Hospital, 300 Longwood Avenue, Boston, MA, 02115, USA. inyang.isong@childrens.harvard.edu.
• J Racial Ethn Health Disparities. 2018 Aug 1; 5 (4): 875-884.

Background/ObjectivesWhile 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 MethodsThis 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.ResultsUnweighted 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.ConclusionRacial/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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