Secular Changes in Waist Circumference, Waist-to-Height Ratio and Body Mass Index in Thai Children

Background: Prevalence of childhood obesity has increased worldwide. Central obesity is an important predictor of the metabolic disorders and cardiovascular risk factors. Waist circumference (WC), waist-to-height ratio (WHtR) and body mass index (BMI) are the commonly used to define central fatness and obesity.

Objective: The study aimed to measure the secular changes and update the reference standards of these parameters for Thai children.

Methods: A cross-sectional survey of 3,885 school children 6.0-12.99 years of age in Ongkharak district of central Thailand was conducted in 2013. Weight, height and WC were recorded by trained staff using sensitive and calibrated instruments. BMI and WHtR were calculated by standard formulae. Age and gender specific smoothened percentile curves were created by using least mean squares method. The data was compared with that from a 2008 cohort from the same area.

Results: BMI, WC and WHtR of boys and girls were comparable at 18.0±4.4 vs 17.8±4.4 kg/m², 61.7±11.8 vs 61.9±11.0 cm and 0.46±0.07 vs 0.46±0.06, respectively. BMI and WC increased but WHtR changed relatively little with age in both genders. In comparison to 2008, BMI were increased by 0.9-1.1 kg/m² in boys and by 0.8-1.1 kg/m² in girls. WC and WHtR have increased consistently across all age groups and both genders. The 75th percentile for WHtR corresponded closely to 0.50 in both genders which has been the suggested cut-off.

Conclusion: There have been significant increases in WC, WHtR and BMI across all age groups and in both genders in Thai children. These findings reflect increasing prevalence of central obesity and are indicators of potential increase in cardio-metabolic health problems in coming years. WC and WHtR should be routinely measured in pediatric examination for early diagnosis of central obesity.