title: Differing associations of BMI and body fat with asthma and lung function in children.
abstract: BACKGROUND
  Current evidence suggests that in children there is a significant, albeit weak, association between asthma and obesity. Studies generally use body mass index (BMI) in evaluating body adiposity, but there are limitations to its use.
  
  
  METHODS
  Children from a population-based study attending follow-up (age 11 years) were weighed, measured and had percent body (PBF) and truncal (PTF) fat assessed using bioelectrical impedance. They were skin prick tested and completed spirometry. Parents completed a validated respiratory questionnaire. Children were defined as normal or overweight according to BMI and PBF cut-offs. We tested the association between these adiposity markers with wheeze, asthma, atopy, and lung-function.
  
  
  RESULTS
  Six hundred forty-six children (339 male) completed follow-up. BMI z-score, PBF, and PTF were all positively associated with current wheeze (odds ratio [95% CI]: 1.27 [1.03, 1.57], P = 0.03; 1.05 [1.00, 1.09], P = 0.03; 1.04 [1.00, 1.08], P = 0.04, respectively). Similar trends were seen with asthma. However, when examining girls and boys separately, significant positive associations were found with PBF and PTF and asthma but only in girls (gender interaction P = 0.06 and 0.04, respectively). Associations between being overweight and wheezing and asthma were stronger when overweight was defined by PBF (P = 0.007, 0.03) than BMI (P > 0.05). Higher BMI was significantly associated with an increase in FEV(1) and FVC, but only in girls. Conversely, increasing body fat (PBF and PTF) was associated with reduced FEV(1) and FVC, but only in boys. No associations between adiposity and atopy were found.
  
  
  CONCLUSIONS
  All adiposity measures were associated with wheeze, asthma, and lung function. However, BMI and PBF did not have the same effects and girls and boys appear to be affected differently.
authors.affiliation: Manchester Academic Health Science Centre, University of Manchester, University Hospital of South Manchester, NHS Foundation Trust, Manchester, UK.
authors.forename: Ran
authors.initials: R
authors.lastname: Wang
authors.forename: Adnan
authors.initials: A
authors.lastname: Custovic
authors.forename: Angela
authors.initials: A
authors.lastname: Simpson
authors.forename: Danielle C
authors.initials: DC
authors.lastname: Belgrave
authors.forename: Lesley A
authors.initials: LA
authors.lastname: Lowe
authors.forename: Clare S
authors.initials: CS
authors.lastname: Murray
mesh_terms: D000273:Adipose Tissue; D050154:Adiposity; D001249:Asthma / Q000453:epidemiology / Q000503:physiopathology*; D015992:Body Mass Index; D002648:Child; D005260:Female; D005541:Forced Expiratory Volume; D006801:Humans; D006967:Hypersensitivity / Q000175:diagnosis / Q000453:epidemiology; D008297:Male; D016017:Odds Ratio; D050177:Overweight / Q000453:epidemiology / Q000503:physiopathology*; D012135:Respiratory Sounds / Q000503:physiopathology*; D012882:Skin Tests; D013147:Spirometry; D014797:Vital Capacity
keywords: adiposity; asthma; bioelectrical impedance; body mass index; pulmonary function