Hearing loss increasing while noise levels rise.
A fascinating study is often cited in discussions of the effect f noise on the aging ear.
In December and January of 1960-61, five researchers traveled to a remote area about 650 miles from Khartoum in the Sudan, bush country surrounded by swamps of the White Nile. There they studied a population remarkable for its simple life and quiet environment. This tribal people, the Mabaans, whose state of cultural development was "late Stone Age" at the time of the research study, was found to have hearing at all ages superior to that of American farmers. Moreover, the Mabaans' hearing did not decline as they grew older.
The researchers considered the quiet of the Mabaan environment to be an important reason for the maintenance of good hearing into old age.
Currently there is evidence closer to home that noise accelerates the changes in the inner ear that accompany aging. Researchers at Central Institute for the Deaf (CID) in St. Louis study chinchillas raised in a quiet environment. William W. Clark of CID says that whereas the chinchillas raised in quiet show some anatomical signs of hearing loss as they age, they do not exhibit loss of hearing sensitivity. In studying 80 chinchillas the researchers found that although the animals lose about 1 percent of the sensory cells in their ears with each year of life, their hearing sensitivity remains normal. In contrast, humans at age 75 may have lost as many as 50 percent of the sensory cells in their ears (the outer hair cells) and have a high-frequency hearing loss.
"Even living in total quiet, there are changes in the ear that accompany aging. However, these changes are not sufficient to cause a hearing loss. In a noisy environment, in contrast, the process is accelerated; there is more extensive anatomical degeneration and more accompanying hearing loss," says Clark.
John H. Mills, professor of otolaryngology and communicative sciences at the Medical University of South Carolina in Charleston and a leading researcher in hearing loss due to aging, notes that many variables besides noise and aging affect the hearing ability of the older person. Among them are genetics, childhood illnesses, drugs taken earlier in life, fat content of diet, cardiovascular health, infections of the ear and bony growth in the middle ear.
Changes in the Ear
Estimates of the percentage of Americans over age 65 with some degree of hearing loss range from 25 to 40 percent.
According to the American Speech-Language-Hearing Association (ASHA), presbycusis -- hearing loss associated with aging -- is most commonly a condition of the aging process itself. Like the rest of the body, the ear and auditory system change as they age.
The loss of hearing sensitivity can be due to chemical and mechanical changes in the inner ear and breakdown of the inner ear structures or to complex degenerative changes occurring within the ear itself and along the nerve pathways leading to the brain. These changes, in turn, can result in a slowing and/or distortion of the signals from the ear to the brain.
Based on current findings, it appears that two types of processes may be associated with aging: one involves changes in the brain pathways (central processing disorder) and the other involves changes in the ear (decrease in hearing sensitivity or hearing loss). The two processes may occur together or separately.
Although presbycusis-linked breakdowns happen to some degree in the outer and middle ear, the most significant structural changes occur in the inner ear and brain pathways.
Noise Can Stimulate Disease Process
Noise not only affects hearing. It also affects other parts of the body and the quality of a person's life.
Researchers have learned that noise:
* increases blood pressure,
* changes the way the heart beats,
* affects the rate of breathing,
* causes an upset stomach or an ulcer,
* contributes to the premature birth of babies,
* make it difficult to sleep, even after the noise stops.
There are other ill effects of noise. It can hamper the performance of daily tasks, affect relationships and emotions, and increase irritability.
Researchers studied the effect of noise on behavior by recording how passers-by responded to a person in need in the presence of noise. While a noisy lawnmower was running, a woman with a broken arm dropped some books and tried to pick them up. No one stopped to help her. When the lawnmower was turned off and the scene repeated, several people stopped to help her retrieve the books.
Excessive noise in a classroom distracts both students and teachers. Researchers compared the test results of students from a school near railroad tracks with the results of students at a school far away from the tracks. They found that the students at the quiet school did much better on the test. Another study found that students whose classrooms face noisy streets do not do as well in school as students in classrooms facing away from noisy streets.
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|Title Annotation:||includes related articles|
|Publication:||Nutrition Health Review|
|Date:||Sep 22, 1991|
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