Socioeconomic status and trajectory of overweight from birth to mid-childhood: the Early Childhood Longitudinal Study-Birth Cohort

Abstract

Objective: Our objective was to use longitudinal data from a US birth cohort to test whether the probability of overweight or obesity during the first 6 years of life varied according to socioeconomic status.

Design and methods: Using six waves of longitudinal data from full-term children in the Early Childhood Longitudinal Study-Birth Cohort (2001-2007; n≈4,950), we examined the prevalence of overweight or obesity (Body Mass Index (BMI)>2 standard deviations above age- and sex- specific WHO Childhood Growth Standard reference mean; henceforth, "overweight/obesity") according to age, socioeconomic status, and race/ethnicity using generalized estimating equation models.

Results: The association between socioeconomic status and overweight/obesity varied significantly by race/ethnicity, but not by sex. Overweight/obesity was significantly associated with socioeconomic status among whites, Hispanics and Asians; the adjusted odds of overweight/obesity began to diverge according to SES after the first 9 months of life. By approximately 4 years, children with the highest SES had a significantly lower odds of overweight/obesity. SES was not significantly related to overweight/obesity among African Americans and American Indians during early childhood.

Conclusions: Few studies have assessed the associations between SES and overweight/obesity within racial/ethnic groups in the US. We find that in contemporary, US-born children, SES was inversely associated with overweight/obesity among more racial/ethnic groups (whites, Hispanics, and Asians) than previously reported.

Figure 1. Predicted probability of overweight/obesity from birth until 5 years of age according to socioeconomic status for each race/ethnic group.

a, b, c: These letters denote p<0.05 for difference in the predicted probability of overweight or obesity at 60 months for each SES quintile. Within each race/ethnic group, the quintiles marked with the same letter are not significantly different from each other whereas those marked with different letters are significantly different. The model included the following variables: SES; race/ethnicity; age; age squared; age cubed; SES by race/ethnicity by age interaction; SES by race/ethnicity interaction; SES by age interaction; race/ethnicity by age interaction; sex; household structure; maternal age. Overweight/obesity is defined as body mass index (BMI) z-score >2 standard deviations (SD) above age- and sex- specific WHO Childhood Growth Standard reference mean at all time points except birth, where we define overweight/obesity as weight-for-age z-score >2 SD above age- and sex- specific WHO Childhood Growth Standard reference mean. To represent socioeconomic status, we used a composite index to capture multiple of the social dimensions of socioeconomic status that incorporates information about maternal and paternal education, occupations, and household income to create a variable representing family socioeconomic status on several domains. We created a 5-category race/ethnicity variable (American Indian/Alaska Native, African American, Hispanic, Asian, white) from the mothers' report of child's race/ethnicity, which originally came 25 race/ethnic categories. To have adequate sample size in race/ethnic categories, we assigned a single race/ethnic category for children reporting more than one race, using an ordered, stepwise approach similar to previously published work using ECLS-B (3).