title: Prenatal and passive smoke exposure and incidence of asthma and wheeze: systematic review and meta-analysis.
abstract: OBJECTIVE
  Exposure to passive smoke is a common and avoidable risk factor for wheeze and asthma in children. Substantial growth in the prospective cohort study evidence base provides an opportunity to generate new and more detailed estimates of the magnitude of the effect. A systematic review and meta-analysis was conducted to provide estimates of the prospective effect of smoking by parents or household members on the risk of wheeze and asthma at different stages of childhood.
  
  
  METHODS
  We systematically searched Medline, Embase, and conference abstracts to identify cohort studies of the incidence of asthma or wheeze in relation to exposure to prenatal or postnatal maternal, paternal, or household smoking in subjects aged up to 18 years old. Pooled odds ratios (ORs) with 95% confidence intervals (CIs) were estimated by using random effects model.
  
  
  RESULTS
  We identified 79 prospective studies. Exposure to pre- or postnatal passive smoke exposure was associated with a 30% to 70% increased risk of incident wheezing (strongest effect from postnatal maternal smoking on wheeze in children aged ≤2 years, OR = 1.70, 95% CI = 1.24-2.35, 4 studies) and a 21% to 85% increase in incident asthma (strongest effect from prenatal maternal smoking on asthma in children aged ≤2 years, OR = 1.85, 95% CI = 1.35-2.53, 5 studies).
  
  
  CONCLUSIONS
  Building upon previous findings, exposure to passive smoking increases the incidence of wheeze and asthma in children and young people by at least 20%. Preventing parental smoking is crucially important to the prevention of asthma.
authors.affiliation: Division of Epidemiology and Public Health, University of Nottingham, City Hospital, UK Centre for Tobacco Control Studies, Nottingham, UK.
authors.forename: Hannah
authors.initials: H
authors.lastname: Burke
authors.forename: Jo
authors.initials: J
authors.lastname: Leonardi-Bee
authors.forename: Ahmed
authors.initials: A
authors.lastname: Hashim
authors.forename: Hembadoon
authors.initials: H
authors.lastname: Pine-Abata
authors.forename: Yilu
authors.initials: Y
authors.lastname: Chen
authors.forename: Derek G
authors.initials: DG
authors.lastname: Cook
authors.forename: John R
authors.initials: JR
authors.lastname: Britton
authors.forename: Tricia M
authors.initials: TM
authors.lastname: McKeever
mesh_terms: D001249:Asthma / Q000453:epidemiology* / Q000209:etiology; D005260:Female; D014943:Global Health; D006801:Humans; D015994:Incidence; D011247:Pregnancy; D011297:Prenatal Exposure Delayed Effects / Q000139:chemically induced / Q000453:epidemiology*; D012135:Respiratory Sounds / Q000209:etiology*; D018570:Risk Assessment; D012307:Risk Factors; D012907:Smoking / Q000009:adverse effects* / Q000453:epidemiology; D011795:Surveys and Questionnaires; D014028:Tobacco Smoke Pollution / Q000009:adverse effects* / Q000706:statistics & numerical data
chemical_list: D014028:Tobacco Smoke Pollution