By David H. Kirkwood
The web this week is alive with the news that one in every five Americans has hearing loss, about double most previous estimates of its incidence.
The source of these alarming reports is an article in the November 14 issue of Archives of Internal Medicine.1 Written by a team of researchers led by Frank Lin, MD, PhD, of the Johns Hopkins School of Medicine, the study concludes that about 48 million Americans age 12 and over have impaired hearing in at least one ear. That’s 20.3% of the total population of those age 12 and older.
Lin et al. derived their findings by analyzing data from the National Health and Nutritional Examination Surveys (NHANES), a research program that has collected health information from thousands of Americans since 1971.
As reports on this week’s article note, the numbers that Lim et al. report are much higher than some earlier estimates that 21 to 29 million Americans have hearing loss.
However, the discrepancy between the new figures and older ones– including the Better Hearing Institute (BHI)/MarkeTrak Survey estimate that 31.5 million Americans had hearing loss in 2004, is far smaller than is being reported.
Lin et al. reached the whopping figure of 48 million Americans over age 12 with hearing loss by including 18 million with hearing loss in only one ear. When they are excluded, the incidence drops to 30 million, which is actually lower than BHI’s figure.
The new study still reports a higher rate of hearing loss: 12.7% compared to BHI’s estimate of 10%. However, that’s because Lin et al. calculated the rate of hearing loss among those 12 and over, since the NHAMES research does not collect data from those under age 12, who have a low rate of hearing loss. BHI’s estimate of 10% is for the entire U.S. population, except for those living in institutions.
WHO’s DEFINITION OF HEARING LOSS USED
Media reports on the Lin et al. study greatly exaggerated differences between their findings and earlier estimates of the incidence of hearing loss. However, that does not detract from the value of the new research by Lin and his co-authors John L. Niparko, MD, also of Johns Hopkins School of Medicine, and Luigi Ferrucci, MD, PhD, of the National Institute on Aging.
In calculating the incidence of hearing loss, they used the World Health Organization’s definition of hearing loss, which is being unable to hear sounds in the speech frequencies that are 25 dB or less. By this standard, about one in eight of Americans 12 and older have hearing loss in both ears.
The scientists found that the prevalence of hearing loss nearly doubled with every decade of age. They also found that women and African-Americans were significantly less likely to have hearing loss at any age than men or than whites and other non-African-Americans.
While unsure of why hearing loss rates varied by gender and race, Lin suggested that the female hormone estrogen and the greater amount of melanin pigment in darker skin could have a protective effect on the inner ear. He said that he and his colleagues plan to investigate this issue in the future.