Waist Circumference, Waist-to Height Ratio and Body Mass Index of Thai Children: Secular Changes and Updated Reference Standards

Background: The prevalence of obesity in pediatric age group has been increasing globally. Body mass index (BMI), waist circumference (WC) and waist-to-height ratio (WHtR) are commonly used to define obesity. The cut-off references for these parameters vary between racial and ethnic groups. We aimed to measure the secular changes and update the reference standards for these three parameters for Thai children in this study. Materials and Methods: We completed a cross-sectional survey of 3,885 school children 6.0-12.99 y of age in Ongkharak district of central Thailand during May to June 2013. Weight, height and WC were recorded by trained staff using sensitive and calibrated instruments. BMI and WHtR were calculated by standard formulae. The summary estimates were described by gender and whole year age groups. 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: Age and gender specific percentile data and curves of WC. WHtR and BMI have been provided for Thai children. BMI and WC increased but WHtR changed relatively little with age in both genders. In comparison to 2008, 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: Since 2008, there have been significant increase in WC and WHtR across all age groups and in both genders in Thai children. These indicate increasing prevalence of central obesity and upcoming cardio-metabolic health problems. This needs to be tackled urgently by creating awareness and promotion of healthy diets and physical activities in school children. WC and WHtR should be routinely measured in paediatric examination for early diagnosis of central obesity.