Hear, Hear, Battered Olde Ears!

As people live longer and the world gets noisier, hearing loss is becoming a major chronic health problem. Technologies, such as cochlear implants, can restore most hearing, but new therapies might one day go deeper by repairing the inner ear's hair cells and protecting them from damage. In the meantime, activists call for quiet.

Of all the chronic diseases of age, hearing loss most directly strains social relationships. A hearing-impaired matriarch might fumble through a chat with her baby boomer son, who began losing his hearing as a teenager. He spent too much time in front of booming concert speakers, and she has put off getting a hearing aid. Now their conversations boil down to a big "huh?"

Far worse, the woman might give up on conversing and become isolated, depressed, and neglectful of her health. "Why, during this time of life when communicating with family and friends is so important, do people allow this to be taken away from them?" asks George Gates, scientific director of the Deafness Research Foundation in Washington, D.C. "People accept that, but it's not OK." Adding insult to injury, he says, some caregivers mistakenly assume that these older people are cognitively impaired.

Yet hearing loss is one of the most common afflictions to creep up late in life. One-third of adults over age 65 and nearly half of those over 75 suffer from it, according to the National Institute on Deafness and Other Communication Disorders in Bethesda, Maryland. Men tend to lose their hearing first, but women follow in their 80s and 90s. By 2015 some 33 million Americans will have trouble hearing, up from 28 million today, says Susan Greco, director of the World Council on Hearing Health in Washington, D.C.

And aging is only part of the story. As the ears gradually lose their sensitivity to sounds, they also must cope with physical damage caused by years of exposure to loud noise. War veterans were battered by ear-splitting gunfire, rock musicians are engulfed by throbbing bass guitars, and carpenters endure the constant screech of woodworking tools. Even "weekend warriors" with their cacophonous leaf blowers, snowplows, and lawnmowers--and children with their bleeping electronic toys--are under siege. An estimated 20% of baby boomers and 12% of school-age children already have impaired hearing, some studies suggest. "As they grow older, their hearing loss will be magnified," says Richard J. H. Smith, an otolaryngologist at the University of Iowa in Iowa City.

Loud noises and aging can trigger the death of hair cells, which react to sound waves by relaying an electrical signal to the brain. Humans start out with about 15,000 of these sensory cells in each ear, and they must last a lifetime. When hair cells die, they cannot be replaced, and their disappearance can lead to gaps in the normal hearing range.

To develop better treatments, researchers are trying to sort out the many ways that the auditory system can malfunction over time. For instance, they know that the inner ear's main power supply--a band of cells rich with energy-producing mitochondria--can wear out. But determining precisely why an older individual has trouble hearing can be difficult, says Laurie Wells, an occupational audiologist and president-elect of the National Hearing Conservation Association in Denver, Colorado: "Looking at [a hearing test], it's impossible to say that x amount of the hearing loss came from aging and y amount came from noise exposure." Scientists do know that aging typically causes high-frequency sounds--such as children's voices and the consonants in everyone's speech--to grow fainter. That’s why many older folks complain that people all sound like they're mumbling, says Wells.

Fortunately, hearing aids and cochlear implants can restore hearing for many people. "Devices are generally becoming smaller, faster, and smarter--more like the real ear," says John Niparko, director of neurotology at Johns Hopkins University in Baltimore, Maryland. His group has found that cochlear implants, which circumvent the hair cells and stimulate the auditory nerve directly, work surprisingly well in older patients. But whether these $25,000 devices will be accessible to everyone in the future remains an open question, says Niparko. Private insurance and Medicare now cover costs for most patients, but that could change. "A lot will depend on how things go economically for the nation and how health care will be covered for seniors," he says.

Additional options for treating hearing loss should become available in the future. Several research groups aim to coax the inner ear to grow new hair cells. The idea isn't so far-fetched, considering that sharks, birds, and reptiles continually repair their own ears this way. Mammals--including humans--have lost the ability but can generate new cells in the ear for a short while after birth, according to studies in mice by Jeffrey T. Corwin, a neuroscientist at the University of Virginia in Charlottesville. Corwin's group is now trying to identify drugs that can kick-start that dormant process in older ears.

Others think that stem cells hold the key to restoring old and damaged ears. Stefan Heller's group at the Massachusetts Eye and Ear Infirmary in Boston recently enticed stem cells taken from mouse embryos or from adult inner ear tissue to turn into hair cells and to integrate properly in a developing chick. Next, the group will try to do the same thing in mammals and eventually in adult animals with auditory damage. Another approach is to use gene therapy to convert other cells in the ear into hair cells--a feat that Yehoash Raphael and his colleagues at the Kresge Hearing Institute at the University of Michigan, Ann Arbor, recently accomplished in guinea pigs.

Some researchers are seeking new strategies to keep hair cells from dying in the first place. One of the most promising possibilities involves the use of antioxidants to protect existing hair cells from the destructive byproducts generated during normal metabolism and stressful insults, including loud noise. Researchers are still doing animal studies to determine which antioxidants work best, at which doses, and for which kinds of hearing loss. If antioxidants can keep hair cells healthy, they might provide the "most straightforward route" to the prevention of hearing loss, says Jochen Schacht, also at Kresge.

In the meantime, activists see plenty of opportunity to conserve hearing the old-fashioned way: by reducing toxic noise. Organizations around the country are lobbying for local noise ordinances to clamp down on blasting boom boxes and roaring motorcycles. Workers are demanding better ear protection to deal with deafening factory noise, and citizen groups are persuading bar owners to distribute earplugs when they feature live bands. In the U.S. Congress, Representative Nita Lowry (D-NY) has introduced the Quiet Communities Act of 2003, which would reestablish the U.S. Environmental Protection Agency's Office of Noise Abatement and Control. If the volume of the noisy world does get turned down, maybe our hearing will survive and we'll finally be able to converse without all the "huhs."

Karen F. Schmidt is a freelance writer in California who is occupationally exposed to the raucous chatter of blue jays.