Objective: To analyse the influence of long-term smoking on the hearing threshold of individuals subjected to occupational noise exposure.
Design: Prospective observational cohort study.
Setting: Occupational health examination of noise-exposed employees in the brick manufacturing industry.
Participants: A study group of long-term smokers (n = 30) and a control group of non-smokers (n = 58) were identified from a population of 227 male noise-exposed employees. Individuals of both groups were employed for 10 years or more at a single brick manufacturing plant. Data on noise exposure, smoking habits, medical and otological history were collected and standard pure tone audiometry was obtained. Exclusion criteria included asymmetrical or conductive hearing loss, uncontrolled systemic illnesses, history of head injury, chronic middle ear pathology or major ear operations.
Main outcome measure: Pure tone audiometry.
Results: Both groups had similar mean age and total duration of occupational noise exposure. The median age-corrected hearing thresholds at 3 and 4 kHz in the smokers group were significantly higher (approximately 7dB) than those in the non-smokers group. No statistical difference in the hearing thresholds between both groups was found in any other tested frequency (0.5, 1, 2, 6 and 8 kHz).
Conclusion: Long-term smokers with occupational noise exposure may, on the basis of this limited study, have a higher risk of developing permanent hearing loss at 3 and 4 kHz when compared with non-smokers with a similar occupational history.