Academic journal article Environmental Health Perspectives

Environmental Cadmium and Lead Exposures and Hearing Loss in U.S. Adults: The National Health and Nutrition Examination Survey, 1999 to 2004

Academic journal article Environmental Health Perspectives

Environmental Cadmium and Lead Exposures and Hearing Loss in U.S. Adults: The National Health and Nutrition Examination Survey, 1999 to 2004

Article excerpt

BACKGROUND: Although cadmium and lead are known risk factors for hearing loss in animal models, few epidemiologic studies have been conducted on their associations with hearing ability in the general population.

OBJECTIVES: We investigated the associations between blood cadmium and lead exposure and hearing loss in the U.S. general population while controlling for noise and other major risk factors contributing to hearing loss.

METHODS: We analyzed data from 3,698 U.S. adults 20-69 years of age who had been randomly assigned to the National Health and Nutrition Examination Survey (NHANES) 1999-2004 Audiometry Examination Component. Pure-tone averages (PTA) of hearing thresholds at frequencies of 0.5, 1, 2, and 4 kHz were computed, and hearing loss was defined as a PTA > 25 dB in either ear.

RESULTS: The weighted geometric means of blood cadmium and lead were 0.40 [95% confidence interval (CI): 0.39. 0.42] [micro]g/L and 1.54 (95% CI: 1.49, 1.60) [micro]g/dL, respectively. After adjusting for sociodemographic and clinical risk factors and exposure to occupational and nonoccupational noise, the highest (vs. lowest) quintiles of cadmium and lead were associated with 13.8% (95% CI: 4.6%, 23.8%) and 18.6% (95% CI: 7.4%, 31.1%) increases in PTA, respectively (p-trends < 0.05).

CONCLUSIONS: Our results suggest that low-level exposure to cadmium and lead found in the general U.S. population may be important risk factors for hearing loss. The findings support efforts to reduce environmental cadmium and lead exposures.

KEY WORDS: cadmium, epidemiology, hearing, lead, NHANES. Environ Health Perspect 120:1544-1550 (2012). http://dx.doi.org/10.1289/ehp.1104863 [Online 31 July 2012]

Hearing loss is one of the most common chronic disabling conditions among older adults (Bainbridge et al. 2008). More than 35 million people [greater than or equal to] 18 years of age suffer from hearing loss in the United States in 2008, and the prevalence of hearing loss tends to increase dramatically with advancing age (Pleis and Lethbridge-Cejku 2006). Loud noise exposure at workplaces (Choi et al. 2012) and from firearms (Agrawal et al. 2009) is a well-established risk factor. A growing body of evidence suggests that exposure to ototoxic environmental and industrial chemicals also may impact the auditory system and lead to hearing loss (Agrawal et al. 2009; Bainbridge et al. 2008).

Experimental studies suggest that lead exposure induces degeneration in the inner ear receptor cells and latency in auditory nerve conduction velocity (Jones et al. 2008; Lasky et al. 1995; Yamamura et al. 1989) and that cadmium exposure causes apoptosis and alters the arrangement of inner ear receptor cells leading to an elevation in auditory thresholds (Kim et al. 2008; Ozcaglar et al. 2001). However, few epidemiologic studies of the association between low-level lead exposure and hearing loss have been conducted in the general population (Park et al. 2010), and there is only one epidemiologic study on cadmium exposure and hearing loss in U.S. adolescents (Shargorodsky et al. 2011).

The aim of this study was to investigate the associations of environmental cadmium and lead exposure with hearing loss in a representative sample of U.S. adults who participated in the National Health and Nutrition Examination Survey (NHANES) 1999-2004, while controlling for important potential confounding factors, including exposure to loud noises at work (occupational), from firearms, and during recreational activities. We also estimated the joint effects of cadmium and lead, as well as effect modification by noise and other potential risk factors.

Methods

Study population. NHANES, which is conducted by the Centers for Disease Control and Prevention (CDC), National Center for Health Statistics (NCHS), is an ongoing series of cross-sectional surveys designed to obtain information from a representative sample of the civilian noninstitutionalized U. …

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