Long-term exposure to ambient air pollutants and hearing loss in Korean adults

Background: Hearing loss is the most prevalent sensory deficit globally, and its prevalence has been growing at a rapid pace, mainly due to aging population. Although there is plentiful evidence that exposure to air pollutants contributes to oxidative stress and free radical formation in inner ear is linked to hearing impairment, there is little awareness of the contribution of air pollution to hearing loss. Objective: To evaluate the associations between long-term exposures to air pollution and hearing loss in Korean adults, while controlling for sociodemographic and clinical factors and occupational, recreational, and firearm noise exposures. Methods: We analyzed data from 15,051 adults in the Korean National Health and Nutrition Examination Survey V (2010-2012). Ambient air pollutant concentrations for participant residing in administrative division and local/town units were collected for current-to-3 years prior to the audiometric examination. Pure-tone average (PTA) of hearing thresholds at speech-frequency (0.5, 1, 2, 4kHz) and high-frequency (3, 4, 6kHz) were computed, and hearing loss was defined as PTA >25dB in either ear. Results: Ambient PM10 was significantly associated with the increased risk of hearing loss at speech-frequency and high-frequency (current year and prior year 3), while CO was significantly associated with the increased risk of hearing loss at speech-frequency (prior year 2 and 3) and high-frequency (prior year 2), when air pollution was assessed at local/town (finer unit). After additional adjustment for regional socioeconomic status and population density (a proxy for traffic noise), NO2 became significantly associated with hearing loss at speech frequency. When air pollution was assessed at administrative division (larger unit), PM10 and CO became stronger and SO2 became significant in hearing loss at speech-frequency. Conclusion: Our results suggest that long-term exposures to environmental PM10, NO2, CO, and SO2 at the levels currently observed in the general population may be risk factors affecting hearing loss.