Occupational Noise, Job Strain and Salivary Cortisol: A Repeated-Measure Study

Abstract

Background:Exposure to occupational noise and job strain have been reported to be associated with the salivary cortisol levels, but the combined effect is not clear. This study aimed to investigate individual and interactive associations between occupational noise exposure and job strain on salivary cortisol levels.Methods:We recruited 120 volunteers in an aircraft manufacturing company in Central Taiwan as study subjects. Each participant was performed 24-hour measurements of noise exposure and collected four salivary samples during different periods on the working day. The enzyme-link immunosorbent assay was applied to determine salivary cortisol levels. We also used questionnaire to obtain information related to job strain, sleep quality and other confounders. Multiple linear regression models were performed to analyze the association.Results:Workers exposed to ≥75 A-weighted decibels (dBA) had a significantly higher difference of salivary cortisol levels between 30-min waking-up and last-night sleep compared with that in workers exposed to <75 dBA and office workers, respectively. Workers exposed to high job strain (Index ≥61) had a significantly higher mean of salivary cortisol levels after 30-min waking-up and a significant difference between 30-min waking-up and last-night sleep than those with the low job strain (Index <61). Subjects co-exposed to noise levels ≥75 dBA and high job strain had a significantly higher mean of salivary cortisol levels after 30-min waking-up (0.371±0.098 mg/dL, P<0.001) and a significant difference between 30-min waking-up and last-night sleep (0.323±0.094 mg/dL, P<0.001) compared with those exposed to <75 dBA and low job strain.Conclusions:Occupational noise exposure and high job strain was associated with the increased salivary cortisol levels after 30-min waking-up. Co-exposure to noise and job strain may have a synergistic interaction with the salivary cortisol levels.