Objective: To determine which aspects of socio-economic status (SES) measured at birth and 9/10 years are associated with body composition at ages 9/10 years.
Design: Mixed longitudinal cohort
Setting: Johannesburg-Soweto South Africa
Participants: A sub-sample of the Birth to Twenty (Bt20) cohort (n=281) with data on birthweight, height, weight, fat and lean tissue (whole body DXA), and birth and 9/10 years SES measures.
Main Outcome Measures: Linear regression was used to estimate the influence of birth and ages 9/10 years SES measures on three outcomes; fat mass index (FMI) (Fat Mass (Kg)/height(m)4), lean mass index (LMI) (lean mass (Kg)/height(m)2), and BMI at ages 9/10 years controlling for sex, age, birthweight and pubertal status.
Results: Compared to the lowest SES tertile, being in the highest birth SES tertile was associated with increased LMI at 9/10 years (β = 0.43, SE = 0.21 for White and Black children and β = 0.50, SE = 0.23 for Black children only), whereas children in the high SES tertile at 9/10 years had increased FMI (β = 0.46, SE = 0.22 for White and Black children and β = 0.65, SE = 0.23 for Black children only). SES at birth and 9/10 years accounted for 8 and 6% of the variance in FMI and BMI respectively (Black children).
Conclusions: These findings underline the importance of examining SES across childhood ages when assessing nutrition inequalities. Results emphasise the need to consider lean and fat mass as well as BMI when studying SES and body composition in children.