title: Body mass index distribution affects discrepancies in weight classifications in children.
abstract: BACKGROUND
  The aim of the present study was to investigate the effect of body mass index (BMI) distribution, ethnicity and age at menarche on the consistency in the prevalence of underweight and overweight defined by the Centers for Disease Control and Prevention (CDC) and the International Obesity Task Force (IOTF) cut-off points in 2-17-year-old Chinese and US children.
  
  
  METHODS
  Data from the China Health and Nutrition Survey (CHNS) 1991 (n= 3895), CHNS 2004 (n= 1902), and the National Health and Nutrition Examination Survey (NHANES) 2003-2004 (n= 3344) were used to define the prevalence of underweight and overweight using the CDC and IOTF BMI cut-off points.
  
  
  RESULTS
  An upward shift in the BMI distribution was observed from the CHNS 1991 to CHNS 2004, and between the CHNS and NHANES 2004. The prevalence of underweight defined by the IOTF cut-off points was higher than that obtained using the CDC cut-off points; absolute differences between IOTF and CDC classifiers were 7%, 5%, and 2% in boys, and 12%, 11%, and 4% in girls in the CHNS 1991, CHNS 2004, and NHANES 2004, respectively. There was a greater consistency in the prevalence of overweight. The consistency of the two classification systems increased with the higher BMI distribution and was not affected significantly by ethnicity or age at menarche.
  
  
  CONCLUSIONS
  The BMI distribution of a population can affect the classification of childhood underweight and overweight differentially as defined by the CDC and IOTF cut-off points, and thus should be considered in the interpretation of results in clinical and population settings.
authors.affiliation: USDA/ARS Children's Nutrition Research Center, Department of Pediatrics, Baylor College of Medicine, Houston, Texas, USA. tuan_72@yahoo.com
authors.forename: Nguyen T
authors.initials: NT
authors.lastname: Tuan
authors.forename: Nancy F
authors.initials: NF
authors.lastname: Butte
authors.forename: Theresa A
authors.initials: TA
authors.lastname: Nicklas
mesh_terms: D000293:Adolescent; D015992:Body Mass Index; D001835:Body Weight / Q000502:physiology; D002648:Child; D002675:Child, Preschool; D005260:Female; D006801:Humans; D008297:Male; D009749:Nutrition Surveys