Distinct patterns of socio-economic disparities in child-to-adolescent BMI trajectories across UK ethnic groups: A prospective longitudinal study

Abstract

Background: In many high-income countries, body mass index (BMI)/obesity levels are inversely associated with socio-economic position (SEP). Little is known whether socio-economic patterns in BMI trajectories throughout childhood differ by ethnicity, especially in the United Kingdom. Objectives: To investigate socio-economic disparities in child-to-adolescent BMI trajectories and risks of overweight and obesity during adolescence across ethnic groups. Methods: Mixed-effects fractional polynomial and multinomial regression models were applied to estimate socio-economic differences in BMI trajectories (3-14 years) and risk of overweight/obesity at 14 years, respectively, in the UK Millennium Cohort Study (n = 15 996). Analysis was stratified by ethnicity. Result: Poverty was associated with higher BMI in children of White and South Asian origins, with a small difference at 3 years, which widened with age to 0.75 kg/m2 (95% CI, 0.59-0.91) and 0.77 kg/m2 (0.26-1.27) at 14 years for the White and South Asian groups, respectively. There was a reverse income-BMI association in children of Black (African-Caribbean) origin with the poverty group having a lower BMI (−0.37 kg/m2 [−0.71 to -0.04] at 5 years; −0.95 kg/m2 [−1.79 to −0.11] at 14 years). These patterns also presented with maternal education as a SEP indicator and for obesity at 14 years. Conclusions: Socio-economic advantage may not be universally associated with lower BMI, which should be considered when planning obesity interventions. The positive SEP-BMI association in children of Black origin requires replication and merits further investigation into underpinning mechanisms.