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04-01-2012 | Speech-language pathology | Article

Low levels of lead exposure may cause hearing loss in teens


Free abstract

MedWire News: Environmental exposure to lead is associated with a markedly increased risk for high-frequency hearing loss, a survey of 12-to-19-year-olds has found.

The finding is significant because blood lead levels in the affected individuals were well below the current "action level" of 10 ug/mL set by the US Centers for Disease Control and Prevention.

"The acceptable level of blood lead in adolescents may need to be reevaluated," warn Josef Shargorodsky (Channing Laboratory, Boston, Massachusetts) and co-authors writing in the Archives of Otolaryngology-Head & Neck Surgery.

Shargorodsky and team examined the cross-sectional association between exposure to heavy metals (lead, mercury, cadmium, and arsenic) and audiometrically determined hearing loss.

They obtained information on all individuals aged 12-19 years who participated in the 2005-2008 National Health and Nutrition Examination Survey. There were 2535 participants with information for analysis of blood lead and mercury levels, 878 for urinary cadmium levels, and 875 for urinary arsenic levels.

Heavy metal exposure varied by demographics, note the authors. For example, blood lead levels were significantly higher in males, individuals of non-Hispanic Black and Hispanic ethnicity, and individuals from families living below the national poverty line, compared with other groups.

Meanwhile, blood mercury levels increased with age while urinary cadmium levels were highest in females and Hispanic individuals. Urinary arsenic levels did not differ by demography.

When participants were divided into quartiles of heavy metal exposure, there were no significant associations between the individual quartiles of lead, mercury, or arsenic exposure and any high- or low-frequency hearing loss risk.

Significantly, however, compared with individuals with blood lead levels of less than 1 µg/dL, individuals with blood lead levels of 2 µg/dL or higher had an increased risk for any hearing loss (odds ratio [OR]=1.9). This was driven by an increase in high-frequency hearing loss (OR=2.22), whereas there was no significant increase in low-frequency hearing loss.

Further analysis confirmed that the link between hearing loss and blood lead levels was consistent across subgroups of gender, income, exposure to loud noise, and smoking history.

The researchers say that their findings "are consistent with previous studies that have demonstrated neurotoxic effects from lead at low levels" and further observe that hearing loss in children and adolescents "can affect learning, speech perception, social skill development, and self-image."

They write: "While the current Centers for Disease Control and Prevention-defined blood lead action level for children is 10 µg/dL, there is evidence that much lower levels may be associated with adverse cognitive and neurologic effects.

"The results of the blood lead analyses in our study are consistent with previous studies that have demonstrated neurotoxic effects from lead at low levels."

By Joanna Lyford

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