Metals, Noise, Diet, and Hearing Loss.

Abstract

Hearing loss is one of the most common chronic health disabilities experienced by older adults, and the prevalence of hearing loss tends to increase dramatically with advancing age. Therefore, identification of modifiable risk factors as well as protective factors is important to lessening the burden of disease associated with hearing loss. The overall aims of this thesis are to assess the impact on hearing loss in the general population of occupational noise exposure, one of the most important known risk factors, and to also assess the potential impacts of exposure to cadmium and lead. This thesis also aimed to assess the potential protective effect of dietary intake, and to investigate whether those dietary intakes lower susceptibility for risk factors on hearing loss. We examined over 3,500 adults of 20 to 69 years of age from the National Health and Nutrition Examination Survey (NHANES) 1999-2004. Our results support the hypothesis that occupational noise exposure increases the risk of hearing loss across various occupations, after controlling for potential confounding factors. Utilization of an occupational noise exposure assessment tool using the Occupational Information Network (O*NET) database allowed us to perform epidemiologic studies of occupational noise exposure in the general population. Our results also support the hypothesis that environmental cadmium and lead exposures increase the risk of hearing loss among adults, particularly those less exposed to noise. Moreover, we found that higher intake of β-carotene, calcium, and an antioxidant composite of β-carotene plus vitamin C reduces the risk of hearing loss, and that higher antioxidants intake acts in synergy in combination with higher calcium and/or magnesium intake to reduce the risk of hearing loss. In particular, those dietary intakes were observed to lower individual susceptibility to the impact of noise on hearing loss, but not likely to affect susceptibility to cadmium and lead exposure in human population. Overall, this thesis provides evidence of the hazardous effects of noise and heavy metals exposures and the protective effect of dietary intake on hearing loss in the general population. Our findings provide preliminary evidence for public health strategies for the prevention and therapeutic treatment of hearing loss.