Hearing loss is one of the most common health complaints of older adults. But today’s technologies are making hearing loss easier to live with, and research is holding promise for new treatments in the future.
“The number of individuals with hearing loss in the United States has doubled over the past three decades, rising from 13.2 million in 1971 to an estimated 28.1 million Americans in 2000,” says Lara Noble, chief audiologist with the Center for Hearing and Speech. “Increased exposure to loud noises, both through recreation and occupation, is one factor attributed to this increase. Americans also are living longer, and it has been documented that 47 percent of adults ages 75 and older have some degree of hearing impairment,” she says, citing information from the American Speech-Language-Hearing Association.
Noble explains that the majority of these cases are attributed to presbycusis, which is hearing loss due to the natural aging process. Additional causes may involve head injury, oto-toxic (ear-damaging) medications, acoustic neuromas (tumors) and Meniere’s disease.
Dr. Richard Chole, Lindburg professor and chairman of otolaryngology, head and neck surgery with Washington University Physicians, says determining the cause of hearing loss involves assessing the condition of the ear canal, eardrum, middle ear bones, inner ear or cochlea, and the auditory nerve itself. Damage or disease affecting any of these parts of the ear can cause hearing loss, and treatment depends on this determination.
“The inner ear—the cochlea—is the most common site of the problem,” Chole says. The cochlea is responsible for turning sound vibrations into nerve signals for the brain to interpret. Small sensory cells, known as ‘hair cells,’ are the mechanisms within the cochlea that allows this to occur. Excessive noise, age or other factors may destroy hair cells and disrupt the transformation of sound waves to nerve signals.
Hearing aids are the most common type of adaptive treatment for people with hearing loss. “Hearing aid technology has improved over the past decade; however, it is important to remember that it is only an aid, not a cure, so things will not be perfect,” Noble says. “Understanding in noisy environments is still a challenge for people with hearing loss, but a combination of older technology (directional microphones) combined with newer digital noise cancellation techniques has helped with understanding in background noise.”
Even as hearing aid technology improves, Chole is working toward new biological treatments that could eventually reverse hearing loss: the regeneration or replacement of inner ear hair cells and nerves. “An investigator in our department is working on a very interesting idea: If a bird loses its hair cells, it can regenerate them. This is unique to birds and amphibians,” he says. Avian hair cells appear identical to human hair cells when examined microscopically. “But, once damaged, a bird’s hair cells regrow. So what is it about the inner ear of a chicken that allows its cells to regrow? My colleague has found a number of genes associated with this regrowth. Other investigators have put those genes into mice, and the mice then regenerate their hair cells.” He adds the preliminary studies are promising, but human trials are still years away.
“The other line of research that is also very exciting is to create a stem cell that can turn into a hair cell and be put into the inner ear,” Chole says. He and his team are exploring the use of adult stem cells, even potentially using those harvested from one’s own body, for hair cell implantation. It is easy to hear the enthusiasm in Chole’s voice as he describes his research, yet he cautions that these new therapies are probably at least a couple decades down the road.
In the meantime, protect your hearing with ear plugs when exposed to loud noise, keep headphones to a reasonable volume (other people shouldn’t be able to hear what’s playing through your earbuds), and talk to your primary-care physician or an audiologist if you need help hearing normal conversation.