title: The synergistic effect of heredity and exposure to second-hand smoke on adult-onset asthma.
abstract: BACKGROUND
  Identification of the subpopulation especially susceptible to the adverse effects of second-hand smoke exposure (SHS) would be useful for preventive actions and interventions.
  
  
  OBJECTIVE
  To investigate whether asthmatic heredity indicates susceptibility to the effects of SHS on the risk of adult-onset asthma.
  
  
  METHODS
  A population-based incident case-control study of clinically defined adult-onset asthma and randomly drawn control subjects (adults 21-63 yr old) from a geographically defined area in South Finland. After excluding current and ex-smokers there were 226 cases and 450 disease-free control subjects.
  
  
  RESULTS
  Our outcome measure was new adult-onset asthma. Parental asthma and recent SHS had a synergistic effect on the risk of asthma, the adjusted odds ratio being 1.97 (95% confidence interval, 1.12-3.45) for SHS; 2.64 (1.65-4.24) for parental asthma; and 12.69 (3.44-46.91) for their joint effect (relative excess risk due interaction, 9.08 [-0.22 to 43.18]). Synergistic effect followed a dose-dependent pattern with both recent and cumulative SHS exposures, with relative excess risk due interaction for parental asthma and over 100 SHS cigarette-years of 6.17 (0.57-19.16).
  
  
  CONCLUSIONS
  This is the first study showing that individuals with asthmatic heredity have a considerably increased risk of adult-onset asthma when exposed to SHS. SHS exposure has dose-dependent synergism with family history of asthma, the joint effect being stronger with higher exposure levels. Avoiding SHS could be an important preventive measure for reducing the risk of adult-onset asthma among those with asthmatic heredity. Asking about family history of asthma is a useful tool for identifying these susceptible individuals in clinical and preventive settings.
authors: 1 Center for Environmental and Respiratory Health Research.
authors: Taina K
authors: TK
authors: Lajunen
authors: Jouni J K
authors: JJ
authors: Jaakkola
authors: Maritta S
authors: MS
authors: Jaakkola
mesh_terms: D000328:Adult; D001249:Asthma / Q000139:chemically induced* / Q000235:genetics*; D016022:Case-Control Studies; D004781:Environmental Exposure / Q000009:adverse effects; D005260:Female; D005387:Finland; D059647:Gene-Environment Interaction; D006801:Humans; D008297:Male; D008875:Middle Aged; D014028:Tobacco Smoke Pollution / Q000009:adverse effects*; D055815:Young Adult
chemical_list: D014028:Tobacco Smoke Pollution