Background: Body mass index as a measure for overweight and obesity is widely accepted. There are no references of BMI for Shanghai adolescents and children.This study was undertaken to construct percentile curves of body mass index (BMI) and cut off points for overweight and obesity of children in Shanghai.

Methods: The data on birthday, height and weight of the 96 104 children from Shanghai (48 790 boys and 47 314 girls) were measured during 1999 to 2002. The BMI percentile curves for Shanghai children aged 0-18 years were constructed by the LMS method. Based on the recommendations of the International Obesity Task Force (IOTF) and the Working Group on Obesity in China (WGOC), the percentile curves passing through 25 and 30 kg/m2 or 24 and 28 kg/m2 at age of 18 were established as overweight and obesity cut off points for Shanghai children.

Results: The age and sex specific BMI percentile curves of Shanghai children were constructed. The BMI in childhood changes substantially with age. The medians at birth are 13.7 and 13.4 kg/m2 for boys and girls, respectively, and increase to 18.3 and 17.8 kg/m2at age of 6 months. They decrease to 15.7 kg/m2 at age of 5.5 years for boys, and 15.4 kg/m2 at age of 6 years for girls, and then increase to 21.4 and 20.1 kg/m2 at age of 18 years for boys and girls respectively. The percentile curves passing through 24 and 28 kg/m2 at age of 18 years are P75.5 and P93.3 for boys, and P89.1 and P98.2 for girls, whereas those passing through 25 and 30 kg/m2 at age of 18 are P82.0 and P96.5 for boys and P93.0 and P99.2 for girls.

Conclusions: Based on the recommendations of the IOTF and WGOC, the BMI cut off points for overweight and obesity for Shanghai children aged 2-18 years have been constructed for the first time in China.

Key words: BMI percentiles; LMS method; children; cut off point