title: Overweight/obesity and risk of seasonal asthma exacerbations.
abstract: BACKGROUND
  Obesity is associated with an increased risk for asthma exacerbations, but whether this risk is related to the season of exacerbation is not known.
  
  
  OBJECTIVE
  To determine the relationship of increased body mass index (BMI) to the season of asthma exacerbation.
  
  
  METHODS
  Study subjects were adult (aged 18-65 years) and children (aged 5-17 years) health plan members with persistent asthma in 2008 for whom a BMI measurement was available. BMI categories were normal (<25 kg/m(2)), overweight (25-29.9 kg/m(2)), and obese (≥30 kg/m(2)). Exacerbations were defined as oral corticosteroid dispensings linked to an asthma encounter in the spring, summer, fall, or winter of 2009.
  
  
  RESULTS
  The cohort included 17,316 adults and 10,700 children. There was a significant (P < .05) linear increase with BMI category in the proportion of adults with exacerbations in every season and in the proportion of children with exacerbations during fall and winter. Relationships of overweight or obesity (vs normal weight) to fall and winter exacerbations remained significant in both adults and children after adjustment for sex and education. In a generalized estimating equation model, both BMI status and season (spring, fall, and winter) were related to exacerbations. Moreover, we noted a significant interaction in adults (P = .03) but not children (P = .97) of the BMI-exacerbation association by season (fall-winter vs spring-summer).
  
  
  CONCLUSIONS
  Higher BMI values increased the risk for asthma exacerbations in adults and children with persistent asthma, particularly for fall-winter exacerbations in adults. Potential mechanisms for these findings, including vitamin D status, viral infections, and corticosteroid responsiveness, merit further study.
authors.affiliation: Department of Allergy, Kaiser Permanente Medical Center, San Diego, Calif. Electronic address: michael.x.schatz@kp.org.
authors.forename: Michael
authors.initials: M
authors.lastname: Schatz
authors.affiliation: Department of Allergy, Kaiser Permanente Medical Center, San Diego, Calif.
authors.forename: Robert S
authors.initials: RS
authors.lastname: Zeiger
authors.affiliation: Department of Research and Evaluation, Kaiser Permanente Medical Center, Pasadena, Calif.
authors.forename: Feng
authors.initials: F
authors.lastname: Zhang
authors.affiliation: Department of Research and Evaluation, Kaiser Permanente Medical Center, Pasadena, Calif.
authors.forename: Wansu
authors.initials: W
authors.lastname: Chen
authors.affiliation: Department of Research and Evaluation, Kaiser Permanente Medical Center, Pasadena, Calif.
authors.forename: Su-Jau
authors.initials: SJ
authors.lastname: Yang
authors.affiliation: Department of Emergency Medicine, Massachusetts General Hospital, Harvard Medical School, Boston, Mass.
authors.forename: Carlos A
authors.initials: CA
authors.lastname: Camargo
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000704:Analysis of Variance; D001249:Asthma / Q000453:epidemiology / Q000209:etiology*; D015992:Body Mass Index; D002140:California / Q000453:epidemiology; D002648:Child; D002675:Child, Preschool; D015331:Cohort Studies; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009765:Obesity / Q000150:complications / Q000453:epidemiology; D050177:Overweight / Q000150:complications* / Q000453:epidemiology; D012307:Risk Factors; D012621:Seasons; D055815:Young Adult
keywords: Asthma; Body mass index; Exacerbation; Obesity; Persistent asthma; Season; Vitamin D