[Study on the body mass index reference norm for defining overweight and obesity in school-age children and adolecents with Uygur and Han ethnic backgrounds in Urumqi].

OBJECTIVE: To construct and compare the body mass index (BMI) cutoff points for defining overweight and obesity in school-age children and youths with Uygur and Han ethnic backgrounds in Xinjiang, China.

METHODS: A total number of 9146 boys and girls in Urumqi, Xinjiang, aged 7-18 years, were recruited by stratifying and clustering sampling from April to June 2004. Demographic and anthropometric data, including body weight and standing height, were collected. Questionnaires and standard methods were used and BMI was calculated by weight/height2. BMI centile curves with age were drawn according to gender and ethnicity, using LMS software (Tim cole and Huiqi Pan) which were making the centile curves passing through 25 kg/m2 and 30 kg/m2, and 24 kg/m2 and 28 kg/m2 at age of 18 for overweight and obesity respectively.

RESULTS: The age and sex specific BMI centile curves were drawn for children with Uygur and Han ethnicities. Data showed that BMI increased with age. The centile of BMI curves, P94.46 and P99.58 for Uygur boys, P92.44 and P99.64 for Uygur girls, P85.05 and P97.26 for Han boys, P90.92 and P99.03 for Han girls, which passing through 25 kg/m2 and 30 kg/m2 by IOTF recommendation at age 18, were constructed. Under the basis of WGOC recommendation, the points that passing through 24 kg/m2 and 28 kg/m2 at age 18 were P90.54 and P98.86 for uygur boys, P86.96 and P98.77 for uygur girls, P78.98 and P94.72 for Han boys, P86.15 and P97.56 for Han girls. The BMI cutoff points for defining overweight and obesity were suggested.

CONCLUSION: To the best of our knowledge, the present study established the BMI cutoff points for Uygur ethnic school-aged children and youths for identifying overweight and obesity. There was ethnic difference in the BMI distribution with age. We recommended using the BMI cutoff points proposed by the current study to identify those overweight and obese children in Urumqi.