BMI, Waist Circumference Reference Values for Chinese School-Aged Children and Adolescents

Background: Childhood obesity has become one of the most serious public health challenges in the 21st century in most developing countries. The percentile curve tool is useful for monitoring and screening obesity at population level, however, in China, no official recommendations on childhood body mass index (BMI) and waist circumference (WC) reference percentiles have been made in practice. Aims: to construct the percentile reference values for BMI and WC, and then to calculate the prevalence of overall and abdominal obesity for Chinese children and adolescents. Methods: A total of 5062 anthropometric records for children and adolescents aged from 7 to 18 years (2679 boys and 2383 girls) were included for analysis. The participants were recruited as part of the national representative "China Health and Nutrition Survey" (CHNS). Age, gender, weight, height, and WC were assessed. Smoothed BMI and WC percentile curves and values for the 3rd, 5th, 10th, 15th, 25th, 50th, 75th, 85th, 90th, 95th and 97th percentiles were constructed by using the Lambda-Mu-Sigma (LMS) method. The prevalence estimates of the overall and abdominal obesity were calculated by using the cut-offs from our CHNS study and the previous "Chinese National Survey on Students' Constitution and Health" (CNSSCH) study, respectively. The difference between prevalence estimates was tested by a McNemar test, and the agreement between these prevalence estimates was calculated by using the Cohen's kappa coefficient. Results: The prevalence values of overall obesity based on the cut-offs from CHNS and CNSSCH studies were at an almost perfect agreement level in boys (kappa = 0.93). However, among girls, the overall obesity prevalence differed between the studies (p < 0.001) and the agreement was weaker (kappa = 0.76). The abdominal obesity prevalence estimates were significant different according to the two systems both in boys and girls, although the agreement reached to 0.88, which represented an almost perfect agreement level. Conclusions: This study provided new BMI and WC percentile curves and reference values for Chinese children and adolescents aged 7-18 years, which can be adopted in future researches. Large longitudinal study is still needed to reveal the childhood growth pattern and validate the inconsistence between different percentile studies.