UC Irvine

Background: Childhood obesity disproportionately affects children from lower-income households, yet the early developmental pathways linking socioeconomic disadvantage to later weight outcomes remain incompletely understood. Self-regulation — a child's ability to control attention, behavior, and emotion — has been proposed as a potential mechanism, given its sensitivity to socioeconomic stress and its links to energy-balance behaviors. Additionally, adiposity rebound, the second rise in BMI typically occurring between ages 5 and 7, is an established early-life marker of obesity risk whose socioeconomic determinants remain unclear. This dissertation uses data from the NICHD Study of Early Child Care and Youth Development (SECCYD), a prospective cohort of 1,364 children recruited at birth from 10 US hospitals, to address three interrelated questions about how early socioeconomic conditions and self-regulatory capacities shape weight trajectories across childhood and adolescence.Methods: In Chapter 1, I examined whether early childhood household income is associated with adiposity rebound timing using propensity score matching in 818 children, followed by modified Poisson regression in approximately 288 matched children. In Chapter 2, I examined whether three domain-specific self-regulation measures — cool self-regulation, food-related hot self-regulation, and nonfood hot self-regulation, assessed between 36 and 54 months — were differentially associated with overweight/obesity at age 15 in 698 children, using modified Poisson regression with sex-stratified analyses. In Chapter 3, I applied counterfactual-based causal mediation analysis to decompose the total effect of early childhood household income on overweight/obesity at age 9 into natural direct and natural indirect effects operating through cool and food-related hot self-regulation in 782 children. Results: In Chapter 1, low household income was not associated with early adiposity rebound in the matched sample (RR=0.91; 95% CI: 0.71–1.17), with consistent null findings across sensitivity analyses. In Chapter 2, cool self-regulation and food-related hot self-regulation were each independently associated with lower overweight/obesity risk at age 15 (cool SR: aRR=0.96 per 10-point increase, 95% CI: 0.93–0.99; food hot SR: aRR=0.78, 95% CI: 0.64–0.96), while nonfood hot self-regulation showed no significant association. The protective association for food-related hot self-regulation was concentrated among boys (aRR=0.64; 95% CI: 0.52–0.78) but not girls. In Chapter 3, although low household income was associated with both higher odds of overweight/obesity at age 9 (adjusted OR=1.54; 95% CI: 1.02–2.33) and poorer self-regulation across both domains, neither domain mediated the income–weight status association; all natural indirect effects were close to null and non-significant. Conclusions: Early childhood household income does not appear to independently shape adiposity rebound timing in this cohort, and socioeconomic disparities in childhood obesity appear to operate through pathways beyond early self-regulatory capacity. These findings are based on a single U.S. birth cohort and warrant replication in other populations. At the same time, domain-specific self-regulation — particularly cool and food-related hot self-regulation — independently predicts adolescent obesity risk, underscoring the value of disaggregating self-regulation constructs in research and intervention design. These findings collectively highlight the importance of structural and environmental mechanisms in linking socioeconomic disadvantage to pediatric obesity and suggest that interventions targeting self-regulation alone may be insufficient to reduce income-related disparities in childhood weight outcomes.