Prevalence of overweight and obesity among primary school children in a developing country: NW-CHILD longitudinal data of 6–9-yr-old children in South Africa

BACKGROUND: Widespread trends of increasing child obesity are reported in developing countries. This longitudinal NW-CHILD study investigated changes in overweight and obesity over a three year period among 574 children between the ages 6 and 9 (282 boys, 292 girls; 407 black, 143 white) in South Africa (SA), taking into consideration sex, race and school type. Stratified random sampling was used to identify 20 schools, across 5 school SES levels (quintiles), in 4 educational districts of the North West Province of SA. Standard anthropometric techniques and international age adjusted BMI cut-off points for children were used to determine overweight and obesity, 3-years apart. Mixed models were used to analyse the effects of sex, race and socio-economic status (SES) of the school. RESULTS: Overall obesity increased over 3-years by 4% from 12.5% at baseline to 16.7% during follow-up. Obesity increased significantly in both white (4.2%) and black (2.0%) children, although overall prevalence in the final year was double (27.3%) in white children compared to black children (13.3%). Prevalence in obesity increased more in boys (3.2%) compared to girls (2.4%), although girls showed a higher overall prevalence (18.5%). SES effects were significant where children in schools associated with higher SES, had the highest rate of increase and the highest prevalence of obesity. A significant change towards an unhealthy BMI was found in 9.2% of the group over the 3-year period, although a small percentage (3.0%) also transitioned towards a healthier BMI. CONCLUSIONS: Overall obesity prevalence rose significantly from 6–9-years. Obesity, compared to overweight, increased more during this period. Prevalence and rate of increase differed markedly in different sexes, race and SES, masking the extent of the problem. Shifting towards an unhealthy BMI was more common than obtaining a healthier BMI over the 3-year period. It also demonstrated the difficulty of breaking the cycle of obesity, once it had started. Early prevention strategies are needed based on the trends established in this study, with special attention to white children living in high SES regions, and black children in economic transition.