Effect of smoking on hearing loss: quality assessment and meta-analysis.
BACKGROUND
There is an accumulating body of research showing that smoking causes hearing loss; however, the results of these studies have been inconsistent.


METHODS
Original English articles were retrieved by MEDLINE search using key words "smoking" and "hearing" (1966-2003). Of 166 relevant studies, those that investigated the risk for hearing loss in smokers identified by pure-tone average were selected for review. Studies with an occupational noise-exposed population were excluded. Methodological quality was assessed by a standardized checklist, and then a meta-analysis was performed on studies with discrete numbers of hearing loss among smokers and nonsmokers.


RESULTS
A total of 15 (10 cross-sectional, 4 cohort, and one case-control) observational studies were identified; the quality scores of the 9 studies with positive associations between smoking and hearing loss were comparable to those of the remaining 6 studies with insignificant associations. Concerning eight analyzable studies, risk ratios (95% confidence intervals) for hearing loss in smokers were 1.33 (1.24, 1.44) for cross-sectional studies, 1.97 (1.44, 2.70) for cohort studies, and 2.89 (2.26, 3.70) for case-control studies, respectively.


CONCLUSIONS
The evidence was suggestive of a positive association between smoking and hearing loss. It is possible that smoking cessation may be a useful strategy for maintaining hearing acuity.
Nomura
Kyoko
K
Department of Hygiene and Public Health, Teikyo University School of Medicine, Itabashi, Tokyo, Japan. kyoko@med.teikyo-u.ac.jp
Nakao
Mutsuhiro
M
Morimoto
Takeshi
T
D016022:Case-Control Studies; D015331:Cohort Studies; D003430:Cross-Sectional Studies; D034381:Hearing Loss / Q000209:etiology*; D006801:Humans; D007564:Japan; D011785:Quality Assurance, Health Care; D012907:Smoking / Q000009:adverse effects*