A case-control study on the relationship of hearing function and blood concentrations of lead, manganese, arsenic,...

Previous research has suggested that heavy metals may be ototoxic in humans, and further, that a reversal of this toxicity may occur when the trace element selenium is present, through formation of metals selenide complexes. This study investigates the relationship between hearing thresholds and blood concentrations of four elements (selenium, lead, manganese, and arsenic) in factory workers, Taiwan. We conducted a hospital-based case-control study with 294 individuals who received the periodic occupational health examination in the Kaohsiung Medical University Hospital. All control subjects (n=173) had normal hearing. Case subjects (n=121) had average hearing threshold over 25 decibels (dB). In all individuals, blood concentrations of lead (Pb), manganese (Mn), arsenic (As), and selenium (Se) were determined by an ICP-MS and standard methods. Possible confounding factors were collected by a questionnaire and medical history reviews. Relationships were analyzed by multiple linear regressions and mixed model. Geometric means of Pb, Mn, As, and Se were determined for case subjects (107.2, 5.5, 17.8, and 229.1 microg/L) and controls (38.9, 5.4, 15.5, and 234.4 microg/L). In our regression models, age, lead and selenium concentrations (logarithmic transformed) were associated significantly with hearing thresholds. In addition, we found that the selenium was inversely associated with hearing thresholds, and may be an antagonist to lead ototoxicty. The present study demonstrated a dose-response relationship between blood lead and hearing thresholds, after adjusting other potential confounders in multiple regressions. In addition, we found that selenium may be a protection element on auditory function. However, additional studies will be needed to clarify the mechanisms of lead toxicity and selenium on the hearing function in molecular and genetic levels.