Waist circumference and body mass index in Chinese children: cutoff values for predicting cardiovascular risk factors

Background: Body mass index (BMI) and waist circumference ( WC) correlate with cardiovascular ( CV) risk factors in childhood which track into adulthood. WC provides a measure of central obesity, which has been specifically associated with CV risk factors. Reference standards for WC, and for WC and BMI risk threshold values are not established in Chinese children. Objectives: To construct reference percentile charts of WC, establish relationships between WC, BMI and other risk factors, and propose WC and BMI threshold values predictive of CV risk factors in Hong Kong ethnic Chinese children. Methods: Weight, height, waist and hip circumference were measured in 2593 (52% boys, 47% girls) randomly sampled Hong Kong school children aged 6-12 years. In 958 of these and 97 additional overweight children (n = 1055), the relationships between WC, BMI, waist/hip and waist/height ratio and six age-adjusted CV risk factors (485% percentile levels of blood pressure ( BP), fasting triglycerides, low-density lipoprotein (LDL) cholesterol, glucose and insulin levels, and < 15% percentile levels of high-density lipoprotein (HDL) cholesterol) were studied. Receiver-operating characteristic analysis was employed to derive optimal age-adjusted sex-specific WC and BMI thresholds for predicting these measures of risk. Results: WC percentiles were constructed. WC correlated slightly more than BMI with CV risk factors and most strongly with insulin and systolic BP, but poorly or not with LDL and glucose. Optimal WC and BMI risk thresholds for predicting four of these six CV risk factors were ca. the 85th percentiles ( sensitivities similar to 0.8, specificities similar to 0.87) with age-specific cutoff values in girls/boys from similar to 57/58 to similar to 71/76cm and 17/18 to 22/23 kg/m(2). Conclusion: These are the first set of WC reference data for Chinese children. WC risk cutoff values are proposed which, despite a smaller waist in Chinese children, are similar to those reported for American children. WC percentiles may reflect population risk.