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Hearing Loss in US Adolescents and Exposure to Heavy Metals: Mercury in Perspective

Hearing Loss in US Adolescents and Exposure to Heavy Metals: Mercury in Perspective Shargorodsky et al1 investigated the association of heavy metals and hearing loss in adolescents; they reported no overall association between quartiles of blood mercury or urinary arsenic levels and hearing loss and found that urinary cadmium and blood lead levels were associated with substantially increased odds of high-frequency hearing loss. They state that the measurement of serum mercury levels is reflective of the “current body burden of the heavy metal as influenced by recent exposure.” As has been discussed previously,2 urine and serum mercury levels are reflective only of recent short-term exposure, not of historical, long-term, or low-dose mercury exposure. This limitation is in part attributable to the very long half-life of mercury in the brain. The authors go on to say, “Longer-term exposure would be better measured by mercury levels in hair.” Again, this statement is not strictly accurate: while hair mercury levels are known to be reflective of exposure to methyl-mercury from fish consumption, they are not reflective of elemental mercury exposure. It is also noteworthy that exposure to elemental, ethyl-mercury, and methyl-mercury (but, ironically, not inorganic mercury) can lead to deposition of inorganic mercury in the brain via the metabolism. However, the National Health and Nutrition Examination Survey collects data on diet, dental health, and vaccinations. Using these data, it should be possible to produce a mercury “exposure index” that might prove more valuable in analyzing the relationship between mercury exposure and hearing deficit. Part of Shargorodsky and colleagues' cohort of adolescents showed a significant change in hearing loss in comparison with an earlier group (1988-1994) that was not readily explicable.3 We note that there have been changes in exposure to mercury over the relevant time periods. For example, during the time frame encompassing the birth of the children included in both studies, 1969 to 1993, there was an increasing number of thimerosal-containing vaccines in the immunization schedule in the United States. In 1999, the cumulative exposure to mercury from vaccines in US children could range from 37.5 μg to 275 μg in children younger than 2 years and from 12.5 μg to 200 μg in in children younger than 6 months.4 We would encourage Shargorodsky and coauthors to look at variations in all sources of mercury, as well as cadmium and lead exposure, to seek or rule out associations between varying exposure to heavy metals and a difference in the hearing deficits between their 2 cohorts. We would also encourage them to perform an analysis to identify potential synergistic toxic reactions between the different heavy metals. Back to top Article Information Correspondence: Dr Rooney, Department of Pharmaceutical and Medicinal Chemistry, Royal College of Surgeons in Ireland, 123 St Stephens Green, Dublin 2, Ireland (jrooney@rcsi.ie). Financial Disclosure: None reported. References 1. Shargorodsky J, Curhan SG, Henderson E, Eavey R, Curhan GC. Heavy metals exposure and hearing loss in US adolescents. Arch Otolaryngol Head Neck Surg. 2011;137(12):1183-118922183895PubMedGoogle ScholarCrossref 2. Rooney JPK. The role of thiols, dithiols, nutritional factors and interacting ligands in the toxicology of mercury. Toxicology. 2007;234(3):145-15617408840PubMedGoogle ScholarCrossref 3. Shargorodsky J, Curhan SG, Curhan GC, Eavey R. Change in prevalence of hearing loss in US adolescents. JAMA. 2010;304(7):772-77820716740PubMedGoogle ScholarCrossref 4. Ball LK, Ball R, Pratt RD. An assessment of thimerosal use in childhood vaccines. Pediatrics. 2001;107(5):1147-115411331700PubMedGoogle ScholarCrossref http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Archives of Otolaryngology - Head & Neck Surgery American Medical Association

Hearing Loss in US Adolescents and Exposure to Heavy Metals: Mercury in Perspective

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Publisher
American Medical Association
Copyright
Copyright © 2012 American Medical Association. All Rights Reserved.
ISSN
0886-4470
eISSN
1538-361X
DOI
10.1001/archoto.2012.907
Publisher site
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Abstract

Shargorodsky et al1 investigated the association of heavy metals and hearing loss in adolescents; they reported no overall association between quartiles of blood mercury or urinary arsenic levels and hearing loss and found that urinary cadmium and blood lead levels were associated with substantially increased odds of high-frequency hearing loss. They state that the measurement of serum mercury levels is reflective of the “current body burden of the heavy metal as influenced by recent exposure.” As has been discussed previously,2 urine and serum mercury levels are reflective only of recent short-term exposure, not of historical, long-term, or low-dose mercury exposure. This limitation is in part attributable to the very long half-life of mercury in the brain. The authors go on to say, “Longer-term exposure would be better measured by mercury levels in hair.” Again, this statement is not strictly accurate: while hair mercury levels are known to be reflective of exposure to methyl-mercury from fish consumption, they are not reflective of elemental mercury exposure. It is also noteworthy that exposure to elemental, ethyl-mercury, and methyl-mercury (but, ironically, not inorganic mercury) can lead to deposition of inorganic mercury in the brain via the metabolism. However, the National Health and Nutrition Examination Survey collects data on diet, dental health, and vaccinations. Using these data, it should be possible to produce a mercury “exposure index” that might prove more valuable in analyzing the relationship between mercury exposure and hearing deficit. Part of Shargorodsky and colleagues' cohort of adolescents showed a significant change in hearing loss in comparison with an earlier group (1988-1994) that was not readily explicable.3 We note that there have been changes in exposure to mercury over the relevant time periods. For example, during the time frame encompassing the birth of the children included in both studies, 1969 to 1993, there was an increasing number of thimerosal-containing vaccines in the immunization schedule in the United States. In 1999, the cumulative exposure to mercury from vaccines in US children could range from 37.5 μg to 275 μg in children younger than 2 years and from 12.5 μg to 200 μg in in children younger than 6 months.4 We would encourage Shargorodsky and coauthors to look at variations in all sources of mercury, as well as cadmium and lead exposure, to seek or rule out associations between varying exposure to heavy metals and a difference in the hearing deficits between their 2 cohorts. We would also encourage them to perform an analysis to identify potential synergistic toxic reactions between the different heavy metals. Back to top Article Information Correspondence: Dr Rooney, Department of Pharmaceutical and Medicinal Chemistry, Royal College of Surgeons in Ireland, 123 St Stephens Green, Dublin 2, Ireland (jrooney@rcsi.ie). Financial Disclosure: None reported. References 1. Shargorodsky J, Curhan SG, Henderson E, Eavey R, Curhan GC. Heavy metals exposure and hearing loss in US adolescents. Arch Otolaryngol Head Neck Surg. 2011;137(12):1183-118922183895PubMedGoogle ScholarCrossref 2. Rooney JPK. The role of thiols, dithiols, nutritional factors and interacting ligands in the toxicology of mercury. Toxicology. 2007;234(3):145-15617408840PubMedGoogle ScholarCrossref 3. Shargorodsky J, Curhan SG, Curhan GC, Eavey R. Change in prevalence of hearing loss in US adolescents. JAMA. 2010;304(7):772-77820716740PubMedGoogle ScholarCrossref 4. Ball LK, Ball R, Pratt RD. An assessment of thimerosal use in childhood vaccines. Pediatrics. 2001;107(5):1147-115411331700PubMedGoogle ScholarCrossref

Journal

Archives of Otolaryngology - Head & Neck SurgeryAmerican Medical Association

Published: Jun 1, 2012

References