Earlier this year, researchers reported in JAMA-Otolaryngology that the overall prevalence of hearing loss in the U.S. continues to decline among adults aged 20 to 69 years, even though adult hearing loss does continue to be linked with increasing age, noise exposure, educational level, ethnicity and gender. Specifically, in their March 2017 article, Hoffman and colleagues concluded there were a 25% reduction in high-frequency hearing impairment, and a 30% reduction in speech frequency hearing impairment in respondents’ worse ear between the 1999 to 2004 cycle of the National Health and Nutrition Examination Survey (NHANES) and the 2011 to 2012 NHANES cycle.
In a June 15 JAMA-Otolaryngology commentary posted online, Esme Fuller-Thomson, PhD, of the University of Toronto, theorized this improved trend in prevalence may be partially due to the phasing out of leaded gasoline.
This elimination of leaded gasoline more than three decades ago is believed to have resulted in an 87% decline in the geometric mean blood lead levels (BLL) in American adults. Published data indicates that BLL went from 13.1 μg/dL in the late 1970s to 1.64 μg/dL by the year 2000.
Numerous studies associate lead exposure to hearing loss. For example, a recent 2011 study by Shargorodsky and colleagues, found that adolescents who had BLL greater than 2 μg/dL had twice the odds of high-frequency hearing loss compared with their peers with BLL of less than 1 μg/dL.
Lead Exposure and Hearing Loss
Although Fuller-Thompson reports that the underlying biomechanics responsible for this beneficial trend associated with phasing lead out of gasoline are unclear, experimental studies with animals have demonstrated that lead exposure can damage receptor cells in the inner ear and impair the function of auditory neurons. Fuller-Thompson went on to mention that bone lead levels should be considered in future studies examining temporal trends in hearing impairment.
The possible linkage between the elimination of leaded gasoline in the 1970s and the overall reduction of hearing loss prevalence in adults is a good example of the role longitudinal public health research plays in the field of audiology.