Occupational exposure to noise and dust in Swedish soft paper mills and mortality from ischemic heart disease and ischemic stroke: a cohort study

Abstract

Objective: To elucidate whether occupational noise exposure increases the mortality from ischemic heart disease (IHD) and stroke, and if exposure to paper dust modified the risks. Methods: We studied 6686 workers from soft paper mills, with occupational noise exposure, < 85 dBA, 85–90 dBA and > 90 dBA, and high (> 5 mg/m3) exposure to paper dust. Person-years 1960–2019 were stratified according to gender, age, and calendar-year. Expected numbers of deaths were calculated using the Swedish population as the reference and standardized mortality ratios (SMR) with 95% confidence intervals (95% CI) were assessed. Results: SMR for IHD was 1.12 (95% CI 0.88–1.41) for noise < 85 dBA, 1.18 (95% CI 0.90–1.55) for 85–90 dBA, and 1.27 (95% CI 1.10–1.47) among workers exposed > 90 dBA. Joint exposure to high noise exposure and high exposure to paper dust resulted in slightly higher IHD mortality (SMR 1.39, 95% CI 1.15–1.67). SMR for ischemic stroke was 0.90 (95% CI 0.37–2.15) for noise < 85 dBA, 1.08 (95% CI 0.45–2.59) for 85–90 dBA, and 1.48 (95% CI 0.99–2.00) among workers exposed > 90 dBA. High noise exposure and high exposure to paper dust resulted in higher ischemic stroke mortality (SMR 1.83, 95% CI 1.12–2.98). Conclusion: Noise levels > 90 dBA was associated with increased IHD mortality. Combined exposures of noise and paper dust may further increase the risks. Our results do not provide support for a causal relationship for ischemic stroke. Residual confounding from smoking has to be considered. Workers need to be protected from occupational noise levels exceeding 90 dBA.