Socioeconomic determinants of childhood obesity among primary school children in Guangzhou, China

BACKGROUND Socioeconomic inequalities in childhood obesity prevalence differ according to a country's stage of nutrition transition. The aim of this study was to determine which socioeconomic factors influence inequalities in obesity prevalence in Chinese primary school children living in an urban setting. METHODS We assessed obesity prevalence among 9917 children aged 5-12 years from a stratified random sample of 29 state-funded (residents) and private (migrants) schools in Guangzhou, China. Height and weight were objectively measured using standardised methods and overweight (+1 SD < BMI-for-age z-score ≤ +2 SD) and obesity (BMI-for-age z-score > +2 SD) were defined using the World Health Organisation reference 2007. Socioeconomic characteristics were ascertained through parental questionnaires. Generalised Linear Mixed Models with schools as a random effect were used to compare likelihood of overweight/obesity among children in private, with public schools, adjusting for child age and sex, maternal and paternal BMI and education level, and household per-capita income. RESULTS The prevalence of overweight/obesity was 20.0 % (95 % CI 19.1 %-20.9 %) in resident compared with 14.3 % (95 % CI 13.0 %-15.4 %) in migrant children. In the adjusted model, the odds of overweight/obesity remained higher among resident children (OR 1.36; 1.16-1.59), was higher in boys compared with girls (OR 2.56; 2.24-2.93), and increased with increasing age (OR 2.78; 1.95-3.97 in 11-12 vs 5-6 year olds), per-capita household income (OR 1.27; 1.01-1.59 in highest vs lowest quartile) and maternal education (OR 1.51; 1.16-1.97 in highest vs lowest). Socioeconomic differences were most marked in older boys, and were only statistically significant in resident children. CONCLUSIONS The socioeconomic gradient for childhood obesity in China is the reverse of the patterns seen in countries at more advanced stages of the obesity epidemic. This presents an opportunity to intervene and prevent the onset of social inequalities that are likely to ensue with further economic development. The marked gender inequality in obesity needs further exploration.