The Protective Role of Zinc Sulfate in Temporary Noise-induced Threshold Shift: a Randomized Clinical Trial Study

Background: Exposure to excessive sound leads to hearing loss. Temporary threshold shifts are defined as threshold shifts that return to baseline levels in the hours to weeks after excessive sound exposure. Aim: This study aimed to examine the zinc sulfate protective effect following noise exposure. Methods: Fifty-two participants with normal audiograms at baseline were randomly assigned to control and intervention groups. First, a distortion product otoacoustic emission test (DPOAEs) was carried out as the baseline assessment, then the intervention group received zinc sulfate supplement capsules for one month and placebo capsules were given to controls. To induce a transient hearing shift, an ABR test was performed. The ABR test was done with 90 dB of sound stimuli for each ear. This input stimulus was a noise exposure that induces a temporary reduction in hearing, in fact, a transient hearing shift has occurred. Then, both groups had a DPOAE test and a follow-up assessment. Signal/noise ratio and DP (distortion product) levels were measured to evaluate the effect of zinc supplement use on transient hearing shift. Results: Comparing the results of the distortion product otoacoustic emission test before and after the auditory brainstem response testing showed significant differences between intervention and control groups (p <0.05). Moreover, the differences in signal/noise ratio between the intervention group before and after ABR testing and also in the control group were significant (p <0.05). Conclusion: Daily zinc sulfate supplement might protect against the transient hearing shift.