Household income, cortisol, and obesity during early childhood: A prospective longitudinal study

OBJECTIVE: To prospectively evaluate the relationship between household income, children's cortisol, and body mass index (BMI) trajectories over a three-year period in early childhood.

STUDY DESIGN: Household income, child hair cortisol levels, and BMI were measured at baseline, 12-, 24-, and 36-month follow-up visits in the NET-Works Study (n=534, children ages 2-4 years and household income < $65,000/year at baseline). Relationships were examined between very low household income (< $25,000/year) at baseline, income status over time (remained < $25,000/year or had increasing income), cortisol accumulation from hair samples, and BMI percent of the 95 th percentile (BMIp95) trajectories using adjusted linear growth curve modeling. Households with baseline income between $25,000-$65,000/year were the reference group for all analyses.

RESULTS: Children from very-low-income households at baseline had annual changes in BMIp95 that were higher (p<0.001) than children from reference group households (0.40 vs. -0.62 percentage units/year). Annual increases in BMIp95 were also greater among children from households that remained very-low-income (p<0.01, 0.34 percentage units/year) and among those with increasing income (p=0.01, 0.51 percentage units/year) compared with the reference group (-0.61 percentage units/year). Children from households that remained very-low-income had higher hair cortisol accumulations (0.22 pg/mg, p=0.02) than reference group children, whereas hair cortisol concentrations of children from households with increasing income (0.03 pg/mg) did not differ significantly from the reference group. Cortisol was not related to BMIp95.

CONCLUSIONS: The economic circumstances of families may impact children's BMI trajectories and their developing stress systems, but these processes may be independent of one another.