title: Combined effect of smoking and occupational exposure to noise on hearing loss in steel factory workers.
abstract: BACKGROUND
  Evidence has accumulated concerning the adverse effects of smoking on hearing acuity, but it is not clear whether smoking modifies the association between exposure to noise and hearing loss.
  
  
  OBJECTIVE
  To examine the synergistic effect of these variables on hearing.
  
  
  METHODS
  Data used were derived from periodic health examinations for 4624 steel company workers in Japan and included audiometry testing and information on smoking habits. Occupational exposure to noise was determined based on company records. Logistic regression was used to examine the dose-response association between smoking and hearing loss. The Cochran-Mantel-Haenszel method was used to calculate the prevalence rate ratio (PRR) of hearing loss for each combination of smoking and noise exposure factors, taking non-smokers not exposed to occupational noise as a reference. The interaction between smoking and noise exposure was assessed using a synergistic index, which equals 1 when the joint effect is additive.
  
  
  RESULTS
  Smoking was associated with increased odds of having high frequency hearing loss in a dose-response manner. The PRR for high frequency hearing loss among smokers exposed to occupational noise was 2.56 (95% CI 2.12 to 3.07), while the PRR for smokers not exposed to noise was 1.57 (95% CI 1.31 to 1.89) and the PRR for non-smokers exposed to noise was 1.77 (95% CI 1.36 to 2.30). The synergistic index was 1.16. Smoking was not associated with low frequency hearing loss.
  
  
  CONCLUSIONS
  Smoking may be a risk factor for high frequency hearing loss, and its combined effect on hearing with exposure to occupational noise is additive.
authors.affiliation: Department of Clinical Epidemiology, Institute of Industrial Ecological Sciences, University of Occupational and Environmental Health, Japan. mizoue@phealth.med.kyushu-u.ac.jp
authors.forename: T
authors.initials: T
authors.lastname: Mizoue
authors.forename: T
authors.initials: T
authors.lastname: Miyamoto
authors.forename: T
authors.initials: T
authors.lastname: Shimizu
mesh_terms: D000328:Adult; D006316:Hearing Loss, High-Frequency / Q000209:etiology*; D006317:Hearing Loss, Noise-Induced / Q000209:etiology*; D006801:Humans; D007564:Japan / Q000453:epidemiology; D008297:Male; D008669:Metallurgy; D008875:Middle Aged; D009623:Noise, Occupational / Q000009:adverse effects*; D009784:Occupational Diseases / Q000209:etiology*; D016273:Occupational Exposure / Q000009:adverse effects*; D012307:Risk Factors; D012907:Smoking / Q000009:adverse effects*