Influence of well-known risk factors for hearing loss in a longitudinal twin study

Abstract

Objective: The aim was to investigate the influence of environmental exposures on hearing loss in a twin cohort. Study sample: Male twins born 1914–1958, representing an unscreened population, were tested for hearing loss at two occasions, 18 years apart. Design: Clinical audiometry and a questionnaire were performed at both time points in this longitudinal study. Noise and solvent exposure were assessed using occupational work codes and a job exposure matrix. Hearing impairment was investigated using two different pure tone averages: PTA4 (0.5, 1, 2, and 4?kHz) and HPTA4 (3, 4, 6, and 8?kHz). Results: Age affected all outcome measures. Noise exposure between time point one and two affected the threshold shifts of PTA4 and HPTA4 more in participants with a pre-existing hearing loss at time point one. Lifetime occupational noise exposure was a risk factor especially for the low-frequency hearing threshold PTA4. Firearm use was a statistically significant risk factor for all outcome measures. Conclusions: Pre-existing hearing loss can increase the risk of hearing impairment due to occupational noise exposure. An increased risk for NIHL was also seen in the group with exposures below 85?dB(A), a result that indicates awareness of NIHL should be raised even for those working in environments where sound levels are below 85?dB(A).