USC Health Now

Age-related hearing loss is more common than previously believed, especially among the generation raised on rock-and-roll music.

USC Health Magazine
Winter 2005
by Monika Guttman

When Ronald Reagan was running for his second presidential term in 1984, the “age issue” was a hot topic. At 73, Reagan was already well beyond the average retirement age. During a televised debate with Walter Mondale, a reporter approached the topic, asking if Reagan was too old to serve another term. “I’m not going to inject the issue of age into this campaign,” said the President. “I am not going to exploit for political gain my opponent’s youth and inexperience.”

The age issue was a big one, recalls John W. House, M.D., clinical professor of otolaryngology at the Keck School of Medicine at USC and president of the world-renowned House Ear Institute. So when Reagan, who was House’s patient, came in during the campaign for a check-up regarding recent hearing loss, “I recommended a hearing aid and I fully expected him to say what many of my older patients say —‘I’m too young to wear a hearing aid’—or, in his case, that age was an issue in his reelection.” Instead, recalls House, “He asked if I thought it would help, and then said he’d like to get one. It took the press two weeks to see the hearing aid, and when they did, hearing aid sales went up 75 percent.”

In the two decades since Reagan’s hearing aid appeared in prime time—and despite the fact that former President Bill Clinton also admitted to using a hearing aid in crowds—little has improved in terms of public understanding and acceptance of presbycusis, otherwise known as age-related hearing loss.

Yet age-related hearing loss is one of the most common conditions affecting older adults, according to the National Institutes of Health. One out of three people over age 60 have some form of hearing loss. By age 80, says House, “almost half the population has a hearing loss serious enough to affect their lives.”

Rock of ages

Over a lifetime, both the external ear and the inner ear experience changes. In the external ear, the ear canal narrows, which can cause an easily remedied buildup of earwax that can temporarily impair hearing. The most common age-related hearing loss, however, occurs from changes in the inner ear. At birth, people have about 15,000 sensory “hair” cell receptors lining the cochlea, the spiral-shaped cavity of the inner ear that contains nerve endings essential for hearing. As people age, these sensory cell receptors degenerate or are damaged, causing a form of hearing loss called sensorineural. Some people lose up to half these cells. This type of loss—also called nerve deafness—can be caused by infections, hereditary problems, trauma and benign tumors, but it is most often a result of aging. The loss usually begins in middle age, occurs in both ears simultaneously, and progresses slowly.

Beginning with high-frequency sounds such as speech, presbycusis slowly steals the ability to distinguish between sounds. Sound pitch or frequency is measured in Hertz (Hz). Although the human ear collects sounds ranging from 1,000-to-20,000 Hz, the 2,000-to-5,000 Hz frequency range is where most of the spectral cues for speech are found. Sound pressure levels are measured in decibels (dB). Normal conversation is measured at a moderate noise level of 50-70 dB, while the extreme noise level of a rock concert might be measured at 100-120 dB.

“Age-related hearing loss begins with difficulties understanding what’s being said in a noisy environment, such as a restaurant or at a party,” explains House. “People with presbycusis tend to complain that other people are mumbling.” The first to go: high-frequency sounds, such as those made by consonants, he says. “So ‘heat’ and ‘eat’ get confused, because you don’t hear that ‘h’ sound.”

For the aging baby-boom generation, research shows exposure to loud rock-and-roll music may be exacerbating the age-related hearing loss. Over-exposure to high-intensity sound is a leading cause of damage to sensory cells. Prolonged exposure to sounds above 85 dB may cause permanent hearing loss. A six-year study by House Ear Institute researchers Rachel Cruz, M.A., and Laurel Fisher, Ph.D., used data collected from hearing screenings conducted at trade shows attended by people working in the music and audio industries.

“This is the first study of this scope to assess hearing loss among professionals in the music and audio industries,” says Cruz, who is a research audiologist. “Study results confirm what we’ve suspected for a long time. These groups not only have high-frequency hearing damage from over-exposure to loud sounds, they also acquire it earlier than individuals in the general population, who may experience a high-frequency hearing loss as they age.”

Experts have known for many years that exposure to too much loud noise produces hearing loss. This condition, known as noise-induced hearing loss, affects construction workers, farmers, musicians, airport workers and people in the armed forces, among others. Sometimes repeated exposure to loud noise causes a ringing, hissing or roaring sound in the ears, called tinnitus. “In previous generations, the hearing loss from loud exposures was found in veterans of World War II, Korea and Vietnam, or people who worked in heavy industry before it became commonplace to wear ear protection,” notes House. “Now we’re seeing people with hearing loss from exposure to loud music. The cause has shifted from war and heavy industry to recreation.”

Sometimes short-duration exposure to sound may only cause temporary hearing loss called a temporary threshold shift. This means that if a sound was first heard at some level of intensity, after over-exposure to loud sounds, that same sound would need to be louder to be heard. A temporary threshold shift usually disappears within 14-16 hours after over-exposure to loud sound. Cumulative over-exposure to loud sounds will eventually result in a permanent threshold shift—a permanent hearing loss.

Age-related hearing loss can be devastating because it lessens the ability to communicate. “People who lose hearing tend to withdraw from social functions,” notes House.

Hearing is not a “use it or lose it” skill that can be practiced. “Right now, this nerve type of hearing loss can’t be corrected by training, by medications or by surgery,” he says. “It can only be treated with amplification via hearing aids.”

Age-related hearing loss has a genetic component. At the House Institute, Rick Friedman, M.D., Ph.D., is the principal investigator of a study on the genetics of hearing loss. Friedman started the study in an attempt to track the genes associated with presbycusis. “This is the most common sensory deficit in the world,” he notes, “so it seemed natural to try to find the genetic basis of this condition.”

Although the study is in its earliest stages, Friedman suspects age-related hearing loss is not due to one single gene but is polygenetic— involving several genes at once. The study, which is enrolling men and women age 65 and over with audiometry-confirmed hearing loss, could eventually lead to medical and genetic interventions that would reverse age-related hearing loss. Friedman also is working with USC colleagues in bioinformatics to try new genomic approaches to finding the hearing-loss gene patterns.

Hear and now

Noise-induced hearing loss is the only type of hearing loss that is completely preventable. Clinicians note several ways to protect and preserve hearing. First and foremost, wear protection in loud situations. “The general rule is that if it’s too loud to carry on a conversation without raising your voice, then it’s too loud for your ears,” House says. He recommends wearing ear protection when using power lawn mowers, listening to live music or firing guns.

In addition, good nutrition and vitamins can help. “Niacin causes vasodilatation—a widening of the arteries—and that helps circulation,” House says. “So does exercise. It’s important to maintain good blood circulation to protect the hair cells.” Limiting caffeine and nicotine intake also can protect hearing and reduce tinnitus.

More good news is that technologic advances are improving options for those with age-related hearing loss. A decade ago, hearing aids did little to help with the earliest stages of sensorineural hearing loss, says House. “However, changes and advances over the past several years have allowed many patients with a sensorineural type hearing loss to benefit greatly from new hearing aid technology,” he says. “With the advent of micro-circuitry, hearing aids are now being designed with computer chips that allow multiple programs to be placed in a single hearing aid. These ‘programmable’ hearing aids can be customized to give an individual the best response. The various programs allow the user to select a specific setting for different listening situations, from a quiet conversation to a noisy meeting place. It is like wearing several interchangeable hearing aids at once.”

New programmable hearing aids also have proven helpful to patients who have a rather severe nerve-type loss that impairs their speech discrimination, and micro-circuitry has made it possible for hearing aids to be miniaturized to the point that, in some cases, the aids can be placed deep in the ear where they take advantage of the normal shape of the external ear and ear canal. “This allows for a better localization of sound and improved resonance,” House says. He recommends that patients wear two hearing aids rather than only one. “Our studies show that patients wearing two hearing aids experience a greater benefit from their amplification. We need both ears in order to identify the direction of sound, and from our ability to tell the direction of sound, we are able to pick out specific voices in a background noise situation. A person wearing only one hearing aid experiences greater difficulty in selecting single voices and discriminating exactly what is being said,” he says.

Those with complete deafness may qualify for a cochlear implant, an electronic device that is surgically implanted in the ear itself, notes Dennis Maceri, M.D., Keck School associate professor of clinical medicine in otolaryngology. Although the devices have been around for more than two decades, newer versions are enhanced by computer technology on a chip inside the implant. “The new devices provide patients with more than four times the amount of auditory information available in other cochlear implants, and because it stimulates all locations of the cochlea simultaneously, it more closely approximates the normally functioning ear,” Maceri says. In addition, bi-directional telemetry permits testing of the electrode in the operating room. Previously, patients had to wait six to eight weeks after surgery to see if the implant was working properly.

Advances also have improved so-called “assistive listening devices.” These devices help the deaf and hard-of-hearing lead a more independent life. They include lights that flash to signal the ringing of the telephone, doorbell or alarm; pillow- or bed-vibrating alarm clocks, and infrared or FM-listening systems that help people hear live performances, presentations, or even watch television at home.

In addition, new devices can target specific hearing problems. Personal listening systems—some are called auditory training systems or loop systems—focus on helping to hear in crowded settings. Others are for one-on-one conversations. Some hearing aids are plugged directly into the television or other auditory device such as radios. Special telephones with a “T-coil” and new telephone receivers work with hearing aids or by themselves to reduce background noise and amplify sound.

“If there is any question about your hearing, you should definitely have it checked by a physician who can help find the right device for the situation,” House advises. Most commonly, however, it is not the person with the hearing loss but the spouse who brings the other person in because they have noticed there is a problem.

“Hearing is one of those issues we definitely take for granted, a ‘hidden’ problem, if you will,” House says. “As we develop more solutions, hopefully more people will seek help for age-related hearing loss. Until then, it is a shame to let vanity get in the way of wearing a hearing aid; you are denying yourself a world filled with wonderful sounds.”

You can get additional information about age-related hearing impairment at the National Institute on Deafness and Other Communication Disorders Web site ww.nidcd.nih.gov/health/hearing/presbycusis.asp .