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Keywords:

  • body mass index;
  • cohort study;
  • obesity;
  • overweight;
  • socio-economic status

Aim:  This paper describes the developmental trajectory of adiposity in relation to socio-demographic status in primary schoolchildren studying in local schools in Hong Kong.

Methods:  Body mass index (BMI) and prevalence of overweight and obesity were determined in a cohort of primary schoolchildren annually from 2001/2002 to 2005/2006. To study the associations between socio-demographic status and adiposity, repeated measures analysis of variance was used for the longitudinal change in BMI, while logistic regression was used with overweight and obesity development as outcomes.

Results:  Prevalence of overweight and obesity was 12.1% and 4.0%, respectively, at baseline, and 16.7% and 3.3%, respectively, at the end of the study period. Boys were more likely to be overweight and obese. Parents in the ‘Professional’ occupational group were less likely to have overweight and obese children. Among 32 781 children with normal weight at baseline, 2885 (8.8%) became overweight or obese after 4 years. Among 6286 children who were initially overweight or obese, 2079 (33.1%) returned to normal weight. Boys were more likely to move up from normal weight to overweight or obesity and less likely to move down the opposite direction during the study period. Parental education at degree level and the occupational group of ‘Professionals’ were, in general, associated with more favourable changes in weight status during follow-up.

Conclusion:  Overweight and obesity were not firmly established during early primary school years. Interventions at the school level on students and their parents might help prevent and control the future development of the obesity epidemic in the population.