Dose-response relationship between smoking and impairment of hearing acuity in workers exposed to noise.

The study included an inquiry and clinical examination of 443 reindeer herders (mean age 43 years) who frequently used noisy tools and vehicles, in particular snowmobiles and chain-saws. Age-adjusted hearing thresholds at 3 and 4 kHz deteriorated significantly with increased exposure to noise. There was the dose-response relationship between the amount of smoking and the impairment of hearing acuity when exposure time to noise was used as covariance. The amount of smoking was not significant until very heavy smoking (more than 144,000 cigarettes, i.e. 20 cigarettes/day for more than 20 years), and no smoking effect could be seen using the classification of current smoking habits. The results support the practice that screening of hearing acuity should be repeated more often in smokers than in non-smokers in noisy work so that hearing damage can be found in an incipient stage and noise-induced hearing loss effectively prevented.