Individual Risk Factors in the Development of Noise-Induced Hearing Loss.

We have analysed the association of noise-induced hearing loss with various risk factors among 685 workers in forest, shipyard, and paper mills. Occupational histories, health, environmental factors, and noise exposures of each worker were retrieved from the database of NoiseScan, our expert program on hearing. The mean hearing level at 4 kHz was 21.5 dB +/- 20.3 dB HL. It correlated significantly with age, noise emission level and noise exposure level. However, these factors could only explain about 2 dB HL of the variation in hearing level. Impulse noise in the shipyard work caused increase in hearing level of 12 dB HL at 4 kHz when compared to steady state noise exposure of forest work. Hearing level correlated with serum cholesterol levels, use of analgesics, blood pressure and smoking. An elevated cholesterol level increased hearing loss in both the high- and low-exposure groups. The use of analgesics did not increase a permanent threshold shift in the low-exposure group, but did in the high-exposure group. Systolic blood pressure, smoking, cholesterol level and the use of painkillers explained 36 % of the variation in hearing level at 4 kHz, whereas noise exposure alone explained 25 % of the corresponding variation.