Heavy Metals Exposure and Hearing Loss in US Adolescents
Introduction Hearing loss is common and, in young persons, can compromise social development and educational achievement. Exposure to heavy metals has been proposed as an important risk factor for hearing loss.
Methods We evaluated the cross-sectional associations between blood lead, blood mercury, and urinary cadmium and arsenic levels and audiometrically determined hearing loss in participants aged 12 to 19 years in the 2005-2008 National Health and Nutrition Examination Survey after accounting for the complex survey design. There were 2535 individuals available for analysis of blood lead and mercury levels, 878 for urinary cadmium levels, and 875 for urinary arsenic levels. Multivariate logistic regression was used to calculate adjusted odds ratios (ORs) and 95% CIs.
Results A blood lead level greater than or equal to 2 μg/dL (to convert to micromoles per liter, multiply by 0.0483) compared with less than 1 μg/dL was associated with increased odds of high-frequency hearing loss (OR, 2.22; 95% CI, 1.39-3.56). Individuals in the highest quartile of urinary cadmium levels had significantly higher odds of low-frequency hearing loss than those in the lowest quartile (OR, 3.08; 95% CI, 1.02-9.25). There was no overall association between quartiles of blood mercury or urinary arsenic levels and hearing loss.
Conclusion Blood lead levels well below the current recommended action level are associated with substantially increased odds of high-frequency hearing loss.
Hearing loss is a common condition in the US population.1 While it is highly prevalent in older adults,2 it is also common in the pediatric age group, with 19.5% of US 6- to 19-year-olds demonstrating evidence of hearing loss.3 Hearing loss is especially damaging in children, as it can impair the development of communication skills and affect educational experience, psychosocial function, and interpersonal relationships.4 Even a slight loss (16-24 dB) may have clinical significance, as it can create a need for speech therapy, auditory training, and special accommodations in school-age children.5
Multiple ototoxic effects of heavy metals, specifically lead, cadmium, arsenic, and mercury, have been suggested.6 Studies have also reported a possible association between lead exposure and an increased risk of hearing loss, especially in children.7,8 In animal models, lead may impair axonal transport, inhibiting auditory processing proximal to the cochlea.9 Animal studies have demonstrated cochlear toxic effects due to cadmium exposure,10 and hearing changes have been observed in children who were exposed to environmental arsenic.11 Also, methyl mercury,12 dimethyl mercury, and mercuric sulfide13 have all been shown to affect auditory brainstem responses.
While studies have reported possible associations between these heavy metals and hearing loss, the evidence is inconclusive. There is also a lack of current US nationally representative analyses of possible associations between these heavy metals and hearing loss in adolescents. Since the federally mandated removal of lead from paint, food containers, plumbing, and gasoline in the 1970s,14 mean blood levels in the United States have decreased dramatically, and most children are now well below the limit of 10 ug/dL (to convert to micromoles per liter, multiply by 0.0483) recommended by the Centers for Disease Control and Prevention15,16; therefore, analyses based on current data are especially important for lead exposure. Therefore, we examined the most recent available data on the association between heavy metal exposure and prevalence of hearing loss in US adolescents and young adults aged 12 to 19 years using the 2005-2006 National Health and Nutrition Examination Survey (NHANES).