Every 63 seconds, another baby boomer over 50 will have difficulty hearing this sentence read aloud. People don't hesitate to turn to eyeglasses for better vision, but the tendency is to take hearing loss less seriously.
More than 28 million Americans -- one in 10 people -- suffer hearing loss, and experts say that most of us don't even know we have a problem.
What's more distressing is that the rock music of youth and the gas-powered leaf blowers and the portable CD players of mid-life -- not to mention the endless noise pollution all around us -- have contributed to declines in hearing at younger ages.
Hearing problems have shot up 26 percent among people ages 46 to 64 since the nation sang to the beat of the Who in the 1970s; and toxic noise is responsible for 17 percent more people between 18 and 44 who have lost their hearing, according to a recent, federally sponsored study.
And while prevention -- turning down the volume on your stereo, for one -- and treatments -- from digital hearing aids and cochlear implants to the promise of anti-oxidant vitamins -- are possibilities, some people are not taking advantage of the offerings.
Many people say they are embarrassed about the loss of hearing and the need to wear hearing aids. Even when someone knows that something is wrong, it can take years before he or she finally seeks a proper diagnosis and then opts for treatment.
The perception of sound is accomplished through an amazing process. The inner ear, or cochlea, contains a string of specialized hair cells that are deflected by sound. When energy, or vibrations, reach these cells, it triggers electrical impulses from the ear to the auditory cortex of the brain. Not only do you hear the sound, but you know what the sound means.
So many things can damage the ears' total 20,000 to 30,000 sensory receptors, or hair cells in the ears -- from high doses of aspirin to antibiotics, genes, noise and smoking -- that by the time we reach 65, one in three people will have trouble understanding the spoken word. The human ear was not built to withstand the loud, chronic noise of modern life, said Dr. Jay Rubinstein, assistant professor of otolaryngology at the University of Iowa.
When enough of these hair cells are damaged, people lose sounds that are normally modulated through those specific cells. Hair cells don't replenish as they do in birds or frogs, so once they are gone, that's it.
Rubinstein said family members are usually the first to notice hearing loss in a loved one. "The television is louder. They are constantly asked to repeat things," he said.
Scientists are trying to understand how a mix of genes and noise works to damage these hair cells. In the past few years, there have been more than 150 genes discovered that may play a role in hearing, and any damage could lead to the loss of hair cells of the inner ear. That could explain why so many people have problems hearing, but it may not be the most important explanation.
Experts say that the inner ear is so sensitive to noise that the sensitivity alone is probably the most common cause of hearing loss. Again, scientists say that a person's genetics contributes to this noise sensitivity.
Richard Salvi, a professor of communicative disorders at the University of Buffalo, said people should avoid exposure to sounds above 85 to 90 decibels, a level the likes of an electric razor at work for 16 hours or a screaming child unstoppable for half that time. Salvi said people can lose hearing after only 30 minutes of close contact with a jet engine at 115 decibels. Some people have even lost hearing after one rock concert, the sounds pulsating at 130 decibels for hours.
Researchers at Harvard and Massachusetts Eye and Ear Institute are just beginning to figure out how noise triggers the death of hair cells. According to M. Charles Liberman, these cells are particularly sensitive to noises that continue unabated. "Break it up and there doesn't seem to be a problem," he said.
Salvi explained that loud, intense sounds -- gunfire, firecrackers -- cause vibrations in the inner ear that literally tear apart the tissue that holds the sensory or hair cells in place. That's the mechanical cause.
But new studies also show that toxic noise also causes metabolic damage. Over time, even moderate but consistent noise stresses the inner ear, producing oxygen free radicals, toxic cellular products that damage many cells of the body, including hair cells. When these hair cells get stressed, the genetic machinery of the cell also starts pumping out harmful products, causing damage.
Rubinstein said that some types of hearing loss affect pure tones, and the death of other hair cells makes it difficult to understand speech. Some people suffer from both problems.