The role of kurtosis and kurtosis-adjusted energy metric in occupational noise-induced hearing loss among metal manufacturing workers

Background Noise energy has been well-established to increase the risk of occupational noise-induced hearing loss (NIHL). However, the role of noise temporal structure (expressed by kurtosis) or its combination with energy metrics (e.g., kurtosis-adjusted cumulative noise exposure, adj-CNE) in occupational NIHL was still unclear. Methods A cross-sectional survey of 867 Chinese workers, including 678 metal manufacturing workers and 189 workers exposed to Gaussian noise, was conducted. Noise energy metrics, including L Aeq,8h and CNE, kurtosis (β), and adj-CNE were used to quantify noise exposure levels. Noise-induced permanent threshold shift at frequencies 3, 4, and 6 kHz (NIPTS 346 ) and the prevalence of high-frequency NIHL (HFNIHL%) were calculated for each participant. The dose–response relationship between kurtosis or adj-CNE and occupational NIHL was observed. Results Among 867 workers, different types of work had specific and independent noise energy and kurtosis values ( p > 0.05). HFNIHL% increased with an increase in exposure duration (ED), L Aeq,8h , CNE, or kurtosis ( p < 0.01), and there were strong linear relationships between HFNIHL% and ED (coefficient of determination [ R 2 ] = 0.963), CNE ( R 2 = 0.976), or kurtosis ( R 2 = 0.938, when CNE < 100 dB(A)∙year). The “V” shape notching extent in NIPTS became deeper with increasing kurtosis when CNE < 100 dB(A)∙year and reached the notching bottom at the frequency of 4 or 6 kHz. The workers exposed to complex noise (β ≥ 10) had a higher risk of NIHL than those exposed to Gaussian noise (β < 10) at the frequencies of 3, 4, 6, and 8 kHz (OR > 2, p < 0.01). Moreover, HFNIHL% increased with adj-CNE ( p < 0.001). There were strong linear relationships between NIHL and adj-CNE or CNE when β ≥ 10 ( R 2 adj-CNE > R 2 CNE ). After CNE was adjusted by kurtosis, average differences in NIPTS 346 or HFNIHL% between the complex and Gaussian noise group were significantly reduced ( p < 0.05). Conclusion Kurtosis was a key factor influencing occupational NIHL among metal manufacturing workers, and its combination with energy metrics could assess the risk of NIHL more effectively than CNE alone.