Preventing Hearing Loss

Scientists discover why we get deafer with age

and how antioxidants might slow the process

Old age brings with it a host of physical woes, and among the most common is

hearing loss. Forty percent of Americans older than 65 suffer from hearing loss,

and by 2030 some 65 million Americans will be hard of hearing.

Now joint work by researchers at the universities of Wisconsin, Florida,

Washington and Tokyo has uncovered the mechanism behind age-related hearing

loss, and with the help of simple chemicals, they have managed to keep old mice

hearing as well as young pups.

The team investigated a molecular mechanism that has been implicated in many

age-related maladies but had not yet been tied to hearing loss. Our bodies are

constantly exposed to short-lived organic molecules known as free radicals, which

harm cells in a process called oxidation. When cells are stressed by oxidative

damage, they release a protein called Bak, which triggers a cascade of events

culminating in cell suicide.

To test whether this mechanism was responsible for age-related hearing loss, the

researchers compared normal mice with genetically engineered mice that do not

have the gene necessary to make Bak. These Bak-deficient mice failed to develop

hearing problems as they aged, but the ordinary mice, subjected to the same

oxidative stress, became hard of hearing. Although most cells in the body are

replaced with new cells after they die, the inner ear’s sensory nerve cells and

ganglion neurons do not regenerate, so hearing loss is permanent.

After determining the cause of hearing loss, the researchers combed through

published literature to see what kind of intervention might stave off free radical

damage. Two antioxidants—molecules that prevent free radicals from harming

cells—stood out: alpha lipoic acid (found in organ meats) and coenzyme Q10

(abundant in meat, fish and poultry). “When we fed [normal] mice these

antioxidants in their food, they were protected from free radical damage in the

cochlea,” says the study’s first author, Shinichi Someya of the University of

Wisconsin–Madison. The team focused exclusively on the inner ear in its studies,

but Someya says other body systems might also benefit from the antioxidants.