As far as age-related changes in hearing are concerned, it’s important to remember that the ear alone is not responsible for hearing. Sound is converted into electrical signals that travel from the cochlea through a series of nerve pathways to the brain for interpretation. In addition to problems associated with physical deterioration of the hair cells in the cochlea, there are age-related changes in the processing ability of the hearing-related nerves (the central processing disorders mentioned earlier) as well as cognitive changes that may slow a person’s ability to understand speech. These changes can have a profound effect on a person’s verbal communication abilities, regardless of whether hearing loss is present. For example, a common complaint of some older people is that people talk too fast. This is because as we age, the mental processes that are needed to understand speech can overload when information is presented too rapidly. In a recent study I conducted at the Veterans Affairs National Center for Rehabilitative Auditory Research (NCRAR) in Portland, Oregon, we found that older people who have poorer performance on certain cognitive tests (those related to thinking, learning, and remembering) also perform poorly on speech recognition tests (tests that use lists of sentences speeded up by a computer).
Age-related hearing loss may not be immediately evident to the person whose hearing is damaged, and as a result, his hearing may be significantly diminished before he seeks help. Indeed, older people may not think they have hearing loss at all. They can still hear a lot of sounds loudly, so they simply think that other people are mumbling. In fact, this type of hearing loss is often noticed first by friends and family who find communication becoming increasingly difficult.
Age-related hearing loss progresses at different rates in different people. Some people still have very little loss even in their 80s, although that isn’t common. It is not clear what makes some people more susceptible to hearing loss than others, but as with any other age-related condition, good nutrition, physical activity, and good prevention practices (hearing protection, in this case) can contribute to lessening the effects or delaying the onset of hearing loss.
Diabetes and hearing loss
The connection between diabetes and hearing loss remains controversial, despite the amount of research that has been devoted to clarifying this issue.
Some of the more common complications of diabetes are damage to blood vessels and to nerves, structures that are both present in the hearing pathway. Because the cochlea has a rich supply of tiny blood vessels that provide nourishment to the various structures involved in hearing, it is susceptible to these effects. There is evidence that high blood pressure in people with diabetes may worsen diabetes-related damage to the small blood vessels in the cochlea, possibly intensifying any high-frequency hearing loss that is already present.
Some studies have found high-frequency loss in people with diabetes, while other studies have found more prevalent hearing loss in the low and middle frequencies in people with diabetes. In a recently completed study at the NCRAR, we tested approximately 800 veterans for hearing loss, about half of whom had diabetes. Although there was a tendency for people with diabetes to have more hearing loss across the entire range of frequencies, the difference was large enough to be significant only in the ultra-high frequencies, beyond the range of frequencies that would normally affect a person’s ability to understand speech. However, this difference was found only in people 60 years old and younger. Over the age of 60, it is likely that age-related hearing loss balances out any difference between people who have diabetes and people who don’t. Because age-related hearing loss typically begins in the high frequencies, the type of hearing loss exhibited by people with diabetes 60 and younger may reveal that the cochlea undergoes early aging in those who have diabetes.