Socio-economic disparities of childhood body mass index in a newly developed population: Evidence from Hong Kong's 'Children of 1997' birth cohort

Background: Childhood adiposity in developed countries is often associated with lower socio-economic position (SEP) of the family and neighbourhood. However, the association of adiposity with SEP varies with national income. The authors examined whether childhood BMI was associated with family or neighbourhood socio-economic characteristics in a recently and rapidly developed Chinese population. Methods: The authors used multilevel modelling in Hong Kong's population-representative 'Children of 1997' birth cohort (n=8327) to examine the association of BMI z-score and overweight (including obesity) at ages 6-11 years with parental education, mother's birthplace, sex and neighbourhood median income. Results: In 7108 (85 % successful follow-up) children, boys were more adipose than girls. The association of parental education with BMI z-score varied with mother's birthplace (p value for interaction 0.001). In children of Hong Kong-born mothers, parental education was negatively associated with BMI z-score (mean difference -0.15, 95% CI -0.25 to -0.05 for highest compared with lowest). However, in children of mainland China-born mothers, parental education was positively associated with BMI z-score (0.18, 95% CI 0.02 to 0.34 in the same comparison). Neighbourhood had no association with BMI z-score. Conclusions: In this recently developed Chinese population, there was no consistent association between socio-economic characteristics and childhood BMI. Other factors, such as experience of economic transition, as proxied by mother's place of birth, exerted a modifying impact. The cultural and biological mechanisms underlying these socio-historical intergenerational influences need to be determined, so that effective interventions can be implemented in China and elsewhere.