Quantitative levels of noise exposure and 20-year hearing decline: findings from a prospective cohort study (the HUNT Study)

Objective We aimed to assess the association between occupational noise exposure and long-term hearing decline. Design This prospective cohort study used linear regression to investigate the association between occupational noise exposure and 20-year hearing decline, adjusted for important confounders. Study sample The Norwegian cohort (N = 4,448) participated in two population-based health studies with pure-tone audiometry; HUNT2 1996–1998 and HUNT4 2017–2019. Exposure assessments included a quantitative job exposure matrix (JEM) and questionnaires. Results The participants (40.2% men, 20–39 years at baseline) had a mean 20-year decline (3–6 kHz) of 11.3 ± 9.8 decibels (dB). There was a positive association between 20-year logarithmic average noise level (JEM-based, LEX,20y) and 20-year hearing decline among men. Compared with no exposure ≥80 dB during follow-up, minimum 5 years of exposure ≥85 dB (JEM-based) predicted 2.6 dB (95% CI: 0.2–5.0) larger 20-year decline for workers aged 30–39 years at baseline, and −0.2 dB (95% CI: −2.2 to 1.7) for workers aged 20–29 years. Combining JEM information with self-reported noise exposure data resulted in stronger associations. Conclusion This large longitudinal study shows an association between JEM-based noise exposure level and increased 20-year hearing decline among men. Contrary to expectations, the associations were weaker among younger workers, which might reflect a latency period.