Cadmium and lead linked to hearing loss in U.S. adults.

Feb 18, 2013

Choi, Y-H, H Hu, B Mukherjee, J Miller and SK Park. 2012. Environmental cadmium and lead exposures and hearing loss in US adults: the National Health and Nutrition Examination Survey, 1999 to 2004. Environmental Health Perspectives

Low levels of lead and cadmium may contribute to hearing loss, according to a large study of U.S. adults. Hearing loss was seen at metal concentrations common in the general population and below current workplace standards. Hearing ability dropped about 14 to 19 percent.

Loud noise can harm hearing but two common metals – lead and cadmium – may have a similar effect, according to a study published in Environmental Health Perspectives.

This study is unique because it links hearing loss and low-level exposures to lead and cadmium in a large sample of men and women in the United States. It is also the first to report cadmium’s effects on hearing in adults.

Hearing loss affects more than 35 million Americans older than 18. Loud noise at work, shooting firearms and environmental and industrial chemicals can damage hearing.

The metal levels found to influence hearing were below national workplace standards set by the Occupational Safety and Health Administration. Although the study does not establish causality, the results support previous animal and humans studies that link these heavy metals to hearing loss.

Animal studies show lead and cadmium have a wide array of toxic effects on the hearing system. Both can affect the inner ear where sound is received and sent on to the brain.

Human studies are limited, but exposure to high levels of lead has been linked to hearing loss in children and males exposed at work. Studies in teens have also linked cadmium exposure to hearing loss.

Lead is banned from gasoline, paint and other products in countries around the world but still lingers in the environment. It is used in other applications, such as electronics and ammunition. In the United States, the most common sources are lead-based paint, contaminated soil, household dust and drinking water.

Cadmium is widely used in products and applications, including batteries, pigments and metal plating. It is also a by-product of ore smelting and may be released in the air from the burning of fossil fuels. Most people are exposed to cadmium through diet, air pollution and smoking.

In this study, researchers looked at the association between hearing loss and exposure to lead and cadmium alone or together in 3,698 U.S. adults aged 20 - 69 years old who were part of the National Health and Nutrition Examination Survey (NHANES) from 1999 - 2004. Participants reported noise exposures through work, firearms or recreation. A hearing exam assessed the severity of hearing loss measured as a pure tone average (PTA).

Hearing was tested at sound frequencies of normal speech so a loss could make it harder to hear conversations. Lead and cadmium were measured in blood samples.

When lead levels were higher, so were cadmium levels. Higher levels of the metals either alone or together related to more hearing loss, especially in older adults.

Adults with the highest lead and cadmium exposures had more hearing loss. Lead levels above 2.8 micrograms per deciliter of blood related to an 18.6 percent rise in PTA and cadmium levels above 0.8 micrograms per liter had a 13.8 percent increase in PTA.

These findings were observed after controlling for other factors associated with hearing loss, including age, sex, education and health problems.

Since lead and cadmium blood levels generally represent recent exposures, using the blood levels to measure long-term, low-level exposures limits the study’s findings.

Nonetheless, the results suggest that exposure to low levels of cadmium and lead may be important risk factors for hearing loss in the general adult population. According to the researchers, “the findings support efforts to reduce environmental cadmium and lead exposures to effectively prevent or delay hearing loss in the general population.”

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