William Murphy, Christa Themann, and Mark Stephenson at the National Institute for Occupational Safety and Health (NIOSH) in Cincinnati studied the hearing test results of more than 5,000 U.S. adults aged 20-69 who identified themselves as members of one of three major ethnic groups in the U.S. They studied the adults' "hearing thresholds," the softest sound an individual could hear, over a range of frequencies. They found that non-Hispanic blacks have on average the best hearing thresholds, non-Hispanic whites the worst, with Mexican Americans in between. Women in general had better hearing compared to men.
Comparing the new hearing data to a similar study 35 years ago with adults aged 25-74, the researchers found the median hearing levels in U.S. adults have not changed much; the hearing of U.S. residents is on average not any worse, nor any better than in the early 1970s. This is somewhat surprising because of the greater number of noise sources now present in our society. One potential factor is that hearing protection was not widely available in the early 1970s. Another speculation for the results is that fewer U.S. residents are working in noisy factory jobs, potentially offsetting the effects of newer noise sources. In addition, it is worth noting that the effects of playing portable music players such as now-ubiqitous iPod too loudly might not yet fully be accounted for, since the analyzed data span the years 1999-2004.
The U.S. adults had their hearing tested as part of a more comprehensive study called the National Health and Nutrition Examination Survey (NHANES). In this study, individuals fill out a survey and receive a comprehensive set of tests in a mobile examination center that travels around the U.S.
Hearing loss can be caused by a myriad of factors, such as age, noise exposure (occupational or recreational), developmental syndromes, infectious disease, physical trauma, ototoxic drugs and chemicals, all of which may be influenced by genetic susceptibility. However, it is estimated that at least one third of the cases of hearing impairment stem from overexposure to noise. Estimates of noise exposure in the United States vary, but range from 5 to 30 million persons exposed in the workplace and 16 to 66 million exposed recreationally. Effective prevention programs could therefore make a large impact in reducing then prevalence of hearing loss in the United States.
On the Web:
Hearing Levels in U.S. Adults, by William J. Murphy, Christa Themann, and Mark Stephenson (a lay-language paper on the ASA meeting's Web site)
The National Health and Nutrition Examination Survey, at the National Center for Health Statistics
American Institute of Physics