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. (C) 2004 The Institute For Cancer Prevention and Elsevier Inc. All rights reserved.