title: Breastfeeding, asthma, and allergy: a tale of two cities.
abstract: BACKGROUND
  The effect of breastfeeding duration on subsequent asthma and allergy remains the subject of much controversy.
  
  
  OBJECTIVE
  To investigate whether differences in study design or disease-related exposure modification were the cause of the differences in study findings.
  
  
  METHODS
  The data from two cohorts, the Childhood Asthma Prevention Study (CAPS) from Australia and the Barn Allergi Miljo Stockholm cohort from Sweden, which had reported different findings on the association between breastfeeding and asthma, were combined. For this analysis, the definitions for breastfeeding, asthma, and allergy were harmonized. Subjects were included if they had at least one parent with wheeze or asthma and had a gestational age of more than 36 wks (combined n = 882). The risk of disease-related exposure modification was assessed using survival analysis.
  
  
  RESULTS
  Breastfeeding reduced the risk of asthma at 4/5 and 8 yrs of age in children with a family history of asthma. The effect was stronger in the Swedish cohort. Breastfeeding had no effect on the prevalence of sensitization to inhaled allergens in this cohort with a family history of asthma but was a risk factor for sensitization to cow's milk, peanuts, and eggs in the CAPS cohort at 4/5 yrs and in the combined cohort at 8 yrs. There was no evidence to support the existence of disease-related exposure modification in either cohort.
  
  
  CONCLUSIONS
  These findings point to the importance of harmonization of features of study design, including subject selection criteria and variable definitions, in resolving epidemiological controversies such as those surrounding the impact of breastfeeding on asthma and allergic sensitization.
authors.affiliation: The Woolcock Institute of Medical Research, Sydney, NSW, Australia.
authors.forename: Bronwyn K
authors.initials: BK
authors.lastname: Brew
authors.forename: Inger
authors.initials: I
authors.lastname: Kull
authors.forename: Frances
authors.initials: F
authors.lastname: Garden
authors.forename: Catarina
authors.initials: C
authors.lastname: Almqvist
authors.forename: Anna
authors.initials: A
authors.lastname: Bergström
authors.forename: Tomas
authors.initials: T
authors.lastname: Lind
authors.forename: Karen
authors.initials: K
authors.lastname: Webb
authors.forename: Magnus
authors.initials: M
authors.lastname: Wickman
authors.forename: Guy B
authors.initials: GB
authors.lastname: Marks
mesh_terms: D000328:Adult; D016902:Air Pollution, Indoor / Q000009:adverse effects; D000485:Allergens / Q000009:adverse effects; D000818:Animals; D001249:Asthma / Q000453:epidemiology* / Q000276:immunology; D001315:Australia / Q000453:epidemiology; D001942:Breast Feeding; D015331:Cohort Studies; D005260:Female; D006801:Humans; D006967:Hypersensitivity / Q000453:epidemiology* / Q000276:immunology; D007223:Infant; D007231:Infant, Newborn; D008297:Male; D011247:Pregnancy; D011297:Prenatal Exposure Delayed Effects / Q000453:epidemiology; D015203:Reproducibility of Results; D012307:Risk Factors; D013548:Sweden / Q000453:epidemiology; D013997:Time Factors; D014028:Tobacco Smoke Pollution / Q000009:adverse effects
chemical_list: D000485:Allergens; D014028:Tobacco Smoke Pollution