title: Relationship of body mass index to percent body fat and waist circumference among schoolchildren in Japan--the influence of gender and obesity: a population-based cross-sectional study.
abstract: BACKGROUND
  Although the correlation coefficient between body mass index (BMI) and percent body fat (%BF) or waist circumference (WC) has been reported, studies conducted among population-based schoolchildren to date have been limited in Japan, where %BF and WC are not usually measured in annual health examinations at elementary schools or junior high schools. The aim of the present study was to investigate the relationship of BMI to %BF and WC and to examine the influence of gender and obesity on these relationships among Japanese schoolchildren.
  
  
  METHODS
  Subjects included 3,750 schoolchildren from the fourth and seventh grade in Ina-town, Saitama Prefecture, Japan between 2004 and 2008. Information about subject's age, sex, height, weight, %BF, and WC was collected from annual physical examinations. %BF was measured with a bipedal biometrical impedance analysis device. Obesity was defined by the following two criteria: the obese definition of the Centers for Disease Control and Prevention, and the definition of obesity for Japanese children. Pearson's correlation coefficients between BMI and %BF or WC were calculated separately for sex.
  
  
  RESULTS
  Among fourth graders, the correlation coefficients between BMI and %BF were 0.74 for boys and 0.97 for girls, whereas those between BMI and WC were 0.94 for boys and 0.90 for girls. Similar results were observed in the analysis of seventh graders. The correlation coefficient between BMI and %BF varied by physique (obese or non-obese), with weaker correlations among the obese regardless of the definition of obesity; most correlation coefficients among obese boys were less than 0.5, whereas most correlations among obese girls were more than 0.7. On the other hand, the correlation coefficients between BMI and WC were more than 0.8 among boys and almost all coefficients were more than 0.7 among girls, regardless of physique.
  
  
  CONCLUSIONS
  BMI was positively correlated with %BF and WC among Japanese schoolchildren. The correlations could be influenced by obesity as well as by gender. Accordingly, it is essential to consider gender and obesity when using BMI as a surrogate for %BF and WC for epidemiological use.
authors: Department of Public Health, Showa University School of Medicine, Tokyo, Japan. h-ochiai@med.showa-u.ac.jp
authors: Hirotaka
authors: H
authors: Ochiai
authors: Takako
authors: T
authors: Shirasawa
authors: Rimei
authors: R
authors: Nishimura
authors: Aya
authors: A
authors: Morimoto
authors: Naoki
authors: N
authors: Shimada
authors: Tadahiro
authors: T
authors: Ohtsu
authors: Emiko
authors: E
authors: Kujirai
authors: Hiromi
authors: H
authors: Hoshino
authors: Naoko
authors: N
authors: Tajima
authors: Akatsuki
authors: A
authors: Kokaze
mesh_terms: D000273:Adipose Tissue / Q000502:physiology*; D000293:Adolescent; D015992:Body Mass Index; D002648:Child; D003430:Cross-Sectional Studies; D005260:Female; D006801:Humans; D007564:Japan / Q000453:epidemiology; D008297:Male; D009765:Obesity / Q000175:diagnosis / Q000453:epidemiology*; D012737:Sex Factors; D055105:Waist Circumference / Q000502:physiology*