Although estimates vary, some 40–50% of adults over the age of 65 years have a measurable hearing impairment, with this figure rising to 83% of those over the age of 70 years. These mean that hearing loss is the third most prevalent chronic medical condition among older adults, after arthritis and hypertension. Beyond the obvious impediment to spoken communication, we have come to realize that there are also hidden effects of hearing loss that may have significant consequences on brain health especially in cognitive function.
The usual reason for worsening hearing in aging is the loss of microscopic hair cells located in the cochlea in the inner ear. There are some 12,000–15,000 outer hair cells whose movement serves as a cochlear amplifier, and 3,000 inner hair cells that change the mechanical vibrations into neural impulses that reach the sound reception areas of the brain. Most notable in age-related hearing loss (presbycusis) is a loss of hair cells in the region of the inner ear that is responsive to the high-frequency sounds that are critically important for the perception of speech. As many older adults know only too well, associated with loss of high-frequency sounds also comes an increased difficulty in hearing speech in the presence of background noise. Common instances of this include the noise of traffic, the babble of multiple conversations in a crowded restaurant, and situations when the acoustic ‘noise’ consists of two people talking at once.
Research has shown that in such a situation like a crowded restaurant hearing the conversation actually requires effort. The brain has to work hard to figure out what is being said and this steals away our awareness and enjoyment of the situation. Researchers have found that this type of ‘effortful listening’ is associated with increased stress responses, changes in pupil dilation, and poorer behavioral performance. Many of us resort to “tuning out” and sitting quietly just nodding our heads hoping nothing really important was being discussed.
The connection between hearing acuity and mental clarity however, may go beyond the effects of stress under conditions of effortful listening. A striking finding from a recent large-scale population study has revealed a strong statistical connection between the appearance and degree of hearing loss and all-cause dementia. One large study showed that in elderly people with hearing loss there was actually a decrease in brain size as measured by volume on MRI testing.
Additionally, people with hearing loss are more likely to avoid social situations, which may impact both physical activity and emotional well being, any of which may mediate the relationship between hearing ability and brain health.
Treating hearing loss as early as possible seems to be a key to prevention of much of this decline in brain function. And in our current world the best possible treatment is properly fitted hearing aids. We listen with our brains. Providing the best hearing possible from the ear to the brain is one aspect that my office, and our excellent Audiologist has done for years successfully.