title: Associations of body fat percent and body mass index with childhood asthma by age and gender.
abstract: OBJECTIVE
  High body mass index (BMI) has been shown to be associated with asthma, but the pattern of this association is still unclear and may differ by gender or stage of puberty. BMI is only a proxy of adiposity, whereas estimation of body fat percent (BF%) by the bioimpedance technique is considered an accurate measure of adiposity. We investigated whether BMI and BF% behave differently in their association with asthma between genders, before and during adolescence.
  
  
  METHODS
  In this cross-sectional study of 10,981 schoolchildren, we used logistic regression models to examine the pattern of association of BMI and BF% with asthma.
  
  
  RESULTS
  In the case of BF%, both the highest (odds ratio [OR]: 1.68, 95% confidence interval [95% CI]: 1.21-2.30) and lowest (OR: 1.59, 95% CI: 1.13-2.23) z-score categories conferred an increased adjusted risk for active asthma. The likelihood ratio test (LRT) of nonlinearity yielded significant results (P < 0.01) for BF%. In contrast, the LRT for BMI yielded a nonsignificant result (P = 0.45) indicating a linear association of asthma with BMI. A unit increase in BMI z-score conferred an increase in the adjusted odds of active asthma (OR: 1.14, 95% CI: 1.02-1.27). In the case of BF%, the adjusted ORs for active asthma at the highest and lowest z-score categories in both genders, before and during adolescence, were similarly elevated, exhibiting a U-shape pattern.
  
  
  CONCLUSIONS
  In contrast to the linear association observed with BMI, BF% displayed a U-shaped association with asthma and may be the preferred measure of adiposity in epidemiological studies of asthma in children.
authors.affiliation: Cyprus International Institute for Environmental & Public Health in Association with Harvard School of Public Health, Cyprus University of Technology, Limassol, Cyprus.
authors.forename: Panayiotis K
authors.initials: PK
authors.lastname: Yiallouros
authors.forename: Demetris
authors.initials: D
authors.lastname: Lamnisos
authors.forename: Ourania
authors.initials: O
authors.lastname: Kolokotroni
authors.forename: Maria
authors.initials: M
authors.lastname: Moustaki
authors.forename: Nicos
authors.initials: N
authors.lastname: Middleton
mesh_terms: D000273:Adipose Tissue / Q000378:metabolism*; D050154:Adiposity; D000293:Adolescent; D000367:Age Factors; D001249:Asthma / Q000150:complications*; D015992:Body Mass Index; D002648:Child; D003430:Cross-Sectional Studies; D005260:Female; D006801:Humans; D008297:Male; D016017:Odds Ratio; D063766:Pediatric Obesity / Q000150:complications*; D012307:Risk Factors; D012737:Sex Factors