Ethnic disparities in childhood BMI trajectories and obesity and potential causes among 29,250 US children: Findings from the Early Childhood Longitudinal Study-Birth and Kindergarten Cohorts.

BACKGROUND/
OBJECTIVES: Study sex- and ethnic-specific childhood BMI growth trajectories of US children, and explore the potential causes of ethnic disparities in childhood BMI trajectories, including household socio-economic status (SES) and parenting practice using nationally representative longitudinal data. SUBJECTS/
METHODS: BMI trajectory curves between 7 months to 16 years of age were fitted using mixed effect models with fractional polynomial functions using pooled 10-year (1998-2008) longitudinal data collected from 29,254 children from two US nationally representative cohorts-Early Childhood Longitudinal Study-Birth (ECLS-B, 2001) and Kindergarten (ECLS-K, 1998-99). A multivariable regression model was used to examine the effects of SES and parenting factors on ethnic disparities in childhood BMI trajectory.
RESULTS: Hispanic boys (HB) and African-American girls (AAG) continuously had the highest prevalence of overweight and obesity (HB: 52.5%, AAG: 49.1% around age of 11) and mean BMI after adiposity rebound than their counterparts. They had the earliest adiposity rebound (age mean [SD]: HB- 57.9 [7.8]; AAG- 59.0 [7.2] months), steeper BMI growth velocity (HB- 5.7 [1.8]; AAG- 7.0 [1.5] 10-2 kg/m2/month), and highest area under curve (HB- 2724.5 [489.8]; AAG- 2681.2 [426.7] kg/m2*month) from adiposity rebound to 16 years of age. The racial/ethnic disparities in childhood BMI trajectories were associated with household SES and family rules for children's regular bedtime (p < 0.05).
CONCLUSIONS: In the US, ethnic disparities in childhood BMI trajectories and obesity are apparent starting from adiposity rebound around age of five. Some minority groups have unfavorable BMI trajectories. These disparities are partially explained by household SES and parenting factors.