Effects of shift work on noise-induced hearing loss.

Evidence has accumulated concerning the adverse effects of noise on hearing acuity, but it is not clear whether working shifts may decelerate the effects of hearing loss. The objective of this study is to assess the effects of shift work on hearing loss in a noisy work environment. A sample of 218 male workers recruited at a semiconductor factory with no known occupational hazards that affected hearing acuity other than noise was chosen. The subjects worked either in an eight-hour or 12-hour shift. A standardized audiometric procedure was performed by a qualified audiologist to measure pure-tone hearing thresholds at 0.5 kHz, 1 kHz, 2 kHz, 3 kHz, 4 kHz, 6 kHz and 8 kHz in both ears. Using multiple linear regression adjusted for age, smoking habits, and work duration, the results showed that the severity of hearing loss in both ears was significantly lower in subjects who worked a 12-hour shift. In conclusion, working a 12-hour shift followed by a day off is best for workers and hearing protection should be provided in high noise areas.