Prevalence of Childhood Obesity in Hong Kong: Comparison Between IOTF and Weight-height Cut-off Standards

Abstract

Objective: To compare the prevalence of childhood obesity in Hong Kong (HK) 2006 by using two different criteria: the International Obesity Taskforce (IOTF) body mass index (BMI) cut off, and local weight-for-height reference (obesity = 120%tile weight-for-height). Method: 29,731 children aged 6-18 years participated in cross-sectional fitness surveys from 2001-2006 using stratified random sampling procedure. Body height and weight were measured by certified fitness instructors. Prevalence of obesity was analyzed using the IOTF (2000) BMI cut-off values and compared with those obtained using the local weigh-height reference values. For the IOTF criteria, age-specific BMI cut-off values for children were extrapolated from adult's BMI cut off points of 25 and 30 kg/m2 for overweight and obesity (Cole, 2000). Whereas for the local standard, those having weight above 20% of the median weight-for-height using 1993 reference values were defined as obese (Leung, 1996). RESULTS: Using local reference, prevalence of childhood obesity in HK 2006 were 22.67% and 16.88% for boys and girls, respectively. When IOTF cut off for obesity were used, the prevalence for boys and girls were 6.33% and 3.08% respectively, which were far below than those obtained from the local reference. However, when IOTF cut off for overweight were used, the prevalence of overweight children was similar to the figures of obesity using local reference. When age and gender specific figures were analyzed, prevalence of obesity using local reference were much higher than that using IOTF cut off for overweight for boys age 16 and above and girls 15 and above. CONCLUSION: IOTF cut off values were extrapolated from adult BMI cutoff of 25 and 30 for overweight and obesity, but not 23 and 25 which were suggested for Asian countries by World Health Organization (2000). Centile curves which drawn from BMI cut off point of 23 and 25 may be more applicable for Asian children. However, discrepancy existed at age after 16 and 15 for boys and girls, respectively. Further effort is needed to explore more appropriate definition of childhood overweight and obesity. It is also suggested to develop relationship between BMI and body fat percentage, morbidity and mortality, so as to provide further insights for determining definitions of obesity.