Effects of noise exposure and long working hours on oxidative stress levels and high-frequency hearing threshold damage in occupational populations.

INTRODUCTION

Occupational noise-induced hearing loss remains a significant public health concern in China. This study aimed to investigate the associations between combined exposure to occupational noise and long working hours with oxidative stress levels and high-frequency hearing loss (HFHL) in an occupational population.

METHODS

A total of 547 Chinese workers from eight manufacturing enterprises in Guangzhou who were engaged in noise-exposed occupations were recruited. Participants were divided into a noise exposure group (weekly working hours ≤40 h, n = 332) and a combined exposure group (weekly working hours >40 h, n = 215). Pure-tone audiometry was performed, and serum levels of superoxide dismutase (SOD), catalase (CAT), malondialdehyde (MDA), and glutathione peroxidase (GPx) were measured using colorimetric microplate assays. Nonparametric tests and binary logistic regression analyses were conducted.

RESULTS

The study included 532 males (97.3%) and 15 females (2.7%). Compared with the noise exposure group, the combined exposure group presented significantly lower SOD activity and CAT activity (p < 0.05) and significantly higher MDA concentration (p < 0.05). The overall prevalence of HFHL was 43.14%, with significantly higher rates in the combined exposure group (p < 0.001). Logistic regression analysis revealed that the levels of SOD (OR = 0.869), CAT (OR = 0.963), and MDA (OR = 1.496) were significantly associated with HFHL. In forward stepwise multivariate analysis, only CAT remained an independent influencing factor (OR = 0.963, 95%CI: 0.941-0.985; p = 0.001).

CONCLUSION

Combined exposure to noise and long working hours is associated with exacerbated oxidative stress and high-frequency hearing loss in occupational populations. CAT acts as an independent protective factor against HFHL, suggesting its potential as a biomarker for hearing damage assessment, although prospective validation is needed.