Is Hearing Loss An Inevitable Part of Aging?

Physicians, the public, and perhaps even some audiologists think that hearing loss is part of normal aging, as shown by the use of the outmoded and inaccurate descriptors “presbycusis” and “age-related hearing loss.” Hearing loss is certainly common with age,¹ but analysis of other conditions common in older people, forgotten studies of hearing in isolated populations not exposed to noise, and recent research support the conclusion that hearing loss with age largely represents noise-induced hearing loss. It’s time to retire the outdated terms and replace them with “sociocusis,”² hearing loss from noise exposure in everyday life, or “noise-induced hearing loss in the elderly.”

Why does this matter? Definitions convey meaning. If an unwanted condition that occurs with age is inevitable, there’s no use trying to prevent it. If, however, the condition is easily preventable, it’s probably worth trying. Unlike many conditions common with aging—muscle weakness, obesity, hypertension, Type II diabetes, heart disease among them—preventing noise-induced hearing loss is easy and inexpensive. Simply avoid loud noise exposure, leave noisy environments, and if one can’t do that, use hearing protection.

The goal of normal or healthy aging has been called “compression of morbidity”³ or “squaring the survival curve.”⁴ Although the biological bases of aging are still not precisely known, with theories based on genetic or biochemical changes in cells and subcellular structures over time,⁵ aging itself is readily apparent. Weight increases, hair thins and turns gray, skin wrinkles, hearing worsens, and eventually everyone dies. That disease, disability, and early death are not part of normal aging is shown by “Blue Zones,”⁶ where many live long and active lives into their 90s. Genetics plays a role, but diet, exercise, social relationships, and a little bit of alcohol appear to prolong healthy functional life. The question is: What is normal aging, and what is abnormal aging? Muscle weakness, obesity, hypertension, diabetes, and heart disease are not inevitable phenomena of normal physiological aging. Neither is hearing loss.

THE IMPORTANCE OF PREVENTION

The impacts of hearing loss are underestimated because it is an invisible disability that usually becomes apparent late in life, when people with hearing loss are retired. There is little economic impact, especially because hearing health care and hearing aids have scant insurance coverage.⁷ Unlike the blind, the hard of hearing can compensate for their hearing loss and readily maintain their independence. Most people think hearing loss is benign.

Of course, that isn’t true. Hearing loss worsens social isolation and is strongly correlated with depression, dementia, falls and death.⁸ Amplification is the only treatment for hearing loss, but due to stigma⁹ and cost only a minority of those who need hearing aids have them.¹⁰ Hearing aids are imperfect and inconvenient substitutes for preserved hearing, so many who acquire them don’t wear them.¹¹

WHAT IS ‘NORMAL’ AGING?

Normal aging is most accurately described by physiological parameters. In males, testosterone levels begin to decrease once maturity is reached. In females, reproductive hormone levels change and menstruation ceases. The basal metabolism rate falls, muscle mass decreases, body fat increases. The cumulative effect of these and other changes can be seen in measures of performance. Even superior athletes’ performance worsens with age. Many findings so common in older people that they are considered “normal” are not, in fact, physiologically normal; instead, they represent abnormal or pathological aging.

Absent specific genetic syndromes, abnormal aging can be ascribed to four basic causes:

• exposures;
• poor quality diet (both quantity and quality);
• disuse atrophy; and
• suboptimal medical care.

Suboptimal medical care refers not to individual patients getting poor quality care, but rather to populations receiving care according to standards later found to have been suboptimal. Better treatment of hypertension, with marked reductions in heart disease and stroke,¹² and advances in dental care that led to reductions in tooth loss,¹³ are examples of better health outcomes from updated standards of care.

Exposures are most relevant to hearing loss. The best analogy for auditory damage from noise exposure may be skin damage from sun exposure. Noise damages delicate cochlear structures, including hair cells and synapses. Ultraviolet light in sunlight causes DNA changes in dermal cells, with the cumulative effect termed photoaging: deep wrinkles, pigmentation changes, and skin cancer.¹⁴ Some sagging (ptosis) of the skin is normal, due to the force of gravity on collagen fibers, but the other changes are not. Without sun exposure, skin remains smooth and unblemished. Without excessive noise exposure, hearing remains undiminished.

EVIDENCE TO CONSIDER

What is the evidence that hearing loss isn’t part of normal physiological aging? A handful of studies published in the 1960s, done to determine the threshold changes of presbycusis, found hearing to be well preserved in isolated populations not exposed to noise. The best known may be that by Rosen et al., who found only a 9-decibel decrement in hearing at 4,000 Hz at age 80 in the Mabaan population in the Sudan.¹⁵ Others studied the Bantu and the Kalahari Bushmen. As Jarvis and van Heerden noted about the Bushmen, “The most striking finding was the absence of presbycusis even in old age.”¹⁶ In 1986, Goycoolea et al. reported that natives of Easter Island who had never left the island had better hearing than islanders who had spent time working on the South American mainland.¹⁷ The length of time on the mainland correlated with the degree of hearing loss. No audiometric difference was found between men and women who had never left the island. All studies showed that in populations not exposed to loud sounds, hearing declined minimally with age. A <10 decibel audiometric decrement with age, not meeting the technical definition of hearing loss, may be normal physiological aging. A 25-40 decibel decrement is not.²

The insight that hearing loss is not part of normal aging is supported by several other lines of evidence, each based on numerous studies published in peer-reviewed scientific journals over many years. Decades of research correlate occupational noise exposure with hearing loss. Girls and women have better hearing than boys and men beginning in the second decade of life, from less exposure to noise from firearms, power tools, and loud music, and then from less occupational noise exposure. Studies show differences in the prevalence of hearing loss in different populations, e.g., urban vs. rural, suggesting an environmental factor causes hearing loss rather than just the passage of time. Both human and animal studies show that hearing loss occurs in the frequencies to which the ear is exposed. And of course, thousands of animal studies demonstrate that noise exposure causes biochemical, genetic, and structural changes in cells and subcellular structures in the auditory system, leading to cell and organelle damage and death, in turn causing noise-induced hearing loss.

From animal research, it was long thought that the main effect of noise was to damage the stria vascularis in the cochlea, ultimately causing hearing loss. This extrapolation of insights from animal research to human ears was incorrect. Based on quantitative microscopic analysis of hair cells, auditory nerve fibers, and strial cells in human ears obtained at autopsy, Wu et al. stated that their 2020 article “upends dogma about the cause of age-related hearing loss.”¹⁸ They found “unexpectedly severe hair cell loss in low-frequency cochlear regions, and dramatically greater loss in high-frequency regions than seen in any aging animal model.” They concluded that “Comparison of normal-aging ears to an age-matched group with acoustic-overexposure history suggests that a lifetime of acoustic overexposure is to blame.”

TIME FOR NEW TERMS?

Hearing loss with age is not an inevitable part of normal aging, but largely represents sociocusis, noise-induced hearing loss from a lifetime of noise exposure. Yes, vascular disease affects hearing, as do ototoxic drugs, ear infections, otosclerosis, and numerous other factors, but the leading cause of hearing loss with age is noise exposure. It’s time to retire the terms “presbycusis” and “age-related hearing loss” and instead use “sociocusis” or “noise-induced hearing loss in the elderly.”

The Centers for Disease Control and Prevention (CDC) found that almost 25% of American adults age 20-69 have noise-induced hearing loss, 53% without significant occupational exposure.¹⁹ Sources of excess noise exposure in everyday life include home appliances, power tools, sound in movies, bars, restaurants, celebrations like birthday parties and weddings, concerts and clubs, sports events, and personal audio system use.²⁰ These and noise exposures from many other sources explain the CDC findings.

Making the world quieter won’t be difficult if society has the will to do it, but first we need to understand that hearing loss with age is noise-induced hearing loss, not an inevitable part of normal aging. Noise control at the source is best—turning down the volume of amplified sound costs nothing. But enforcement of existing noise ordinances would help, and product noise labeling could be legislated.

Acknowledgement: This article is adapted from a paper presented at the 12th Congress of the International Commission on Biological Effects of Noise in Zurich, Switzerland on June 20, 2017.²¹

Article courtesy of https://journals.lww.com/thehearingjournal