title: Obesity and asthma: an association modified by age of asthma onset.
abstract: BACKGROUND
  Studies of asthma phenotypes have identified obesity as a component of a group characterized by a high proportion of subjects with adult-onset asthma. However, whether age of asthma onset modifies the association between obesity and asthma is unknown.
  
  
  OBJECTIVE
  We sought to compare the associations between body mass index (BMI) categories with physiological, inflammatory, and clinical parameters across age of asthma onset phenotypes; and to compare the rate of BMI change in relation to asthma duration, by age of onset asthma phenotypes.
  
  
  METHODS
  From the Severe Asthma Research Program, we defined age of asthma onset as early (<12 years of age) and late (≥12 years of age). Comparisons of BMI categories were done within age-of-onset groups, and obesity was also compared across these groups. Multivariable logistic regression analysis was done to evaluate the association between BMI categories with health care use and respiratory symptoms and multivariable linear regression for the association between duration of asthma and weight gain (BMI change per year). An interaction between obesity and age of asthma onset was included in the multivariable analyses.
  
  
  RESULTS
  The study population consisted of 1049 subjects, and the median age for asthma onset was 10 years (interquartile range, 4-25 years); 48% had late-onset asthma (≥12 years of age), and 52% had early-onset asthma (<12 years of age). Compared with obese subjects with late-onset asthma, obese subjects with early-onset asthma had more airway obstruction, bronchial hyperresponsiveness, and higher odds ratios of ever having 3 or more previous oral steroid tapers per year or intensive care unit admissions for asthma per preceding year (interactions between obesity and age of asthma onset were P = .055 and P = .02, respectively). In subjects with early-onset asthma but not in subjects with late-onset asthma, there was a significant association between increasing BMI and duration of asthma after adjusting for confounders. The interaction between asthma duration and age of asthma onset was a P value of less than .01.
  
  
  CONCLUSIONS
  Asthmatic subjects are differentially affected by obesity based on whether they had asthma early (<12 years of age) or later in life. These results highlight the need to understand obesity as a comorbidity that affects specific clinical phenotypes and not all asthma subjects alike.
authors.affiliation: Asthma Institute, Pulmonary Allergy and Critical Care Medicine, University of Pittsburgh, Pittsburgh, PA, USA. holguinf@upmc.edu
authors.forename: Fernando
authors.initials: F
authors.lastname: Holguin
authors.forename: Eugene R
authors.initials: ER
authors.lastname: Bleecker
authors.forename: William W
authors.initials: WW
authors.lastname: Busse
authors.forename: William J
authors.initials: WJ
authors.lastname: Calhoun
authors.forename: Mario
authors.initials: M
authors.lastname: Castro
authors.forename: Serpil C
authors.initials: SC
authors.lastname: Erzurum
authors.forename: Anne M
authors.initials: AM
authors.lastname: Fitzpatrick
authors.forename: Benjamin
authors.initials: B
authors.lastname: Gaston
authors.forename: Elliot
authors.initials: E
authors.lastname: Israel
authors.forename: Nizar N
authors.initials: NN
authors.lastname: Jarjour
authors.forename: Wendy C
authors.initials: WC
authors.lastname: Moore
authors.forename: Stephen P
authors.initials: SP
authors.lastname: Peters
authors.forename: Michael
authors.initials: M
authors.lastname: Yonas
authors.forename: W Gerald
authors.initials: WG
authors.lastname: Teague
authors.forename: Sally E
authors.initials: SE
authors.lastname: Wenzel
mesh_terms: D000293:Adolescent; D000328:Adult; D017668:Age of Onset; D000368:Aged; D001249:Asthma / Q000150:complications* / Q000453:epidemiology / Q000473:pathology / Q000503:physiopathology; D015992:Body Mass Index; D002648:Child; D005260:Female; D005541:Forced Expiratory Volume; D006801:Humans; D016015:Logistic Models; D008297:Male; D008875:Middle Aged; D015999:Multivariate Analysis; D009765:Obesity / Q000150:complications* / Q000473:pathology; D010641:Phenotype; D011788:Quality of Life; D012720:Severity of Illness Index; D013997:Time Factors; D014481:United States / Q000453:epidemiology; D055815:Young Adult