Study Links Cognitive Deficits, Hearing Loss

There’s another reason to be concerned about hearing loss — one of the most common health conditions in older adults and one of the most widely undertreated. A new study by researchers at Johns Hopkins Medicine suggests that elderly people with compromised hearing are at risk of developing cognitive deficits — problems with memory and thinking — sooner than those whose hearing is intact.

The study in JAMA Internal Medicine was led by Dr. Frank Lin, a hearing specialist and epidemiologist who over the past several years has documented the extent of hearing problems in older people and their association with falls and the onset of dementia.

The physician’s work is bringing fresh, and some would say much-needed, attention to the link between hearing difficulties and seniors’ health.

In his new report, Dr. Lin looked at 1,984 older adults who participated over many years in the Health ABC Study, a long-term study of older adults conducted in Pittsburgh and Memphis. Participants’ mean age was 77; none had evidence of cognitive impairment when the period covered by this research began. In 2001 and 2002, they received hearing tests and cognitive tests; cognitive tests alone were repeated three, five and six years later.

The tests included the Modified Mini-Mental State exam, which is administered through an interview and yields an overall picture of cognitive status, and the Digit Symbol Substitution Test, a paper-only exercise that asks people to match symbols and numbers, which can reveal deficits in someone’s working memory and executive functioning.

Dr. Lin found that annual rates of cognitive decline were 41 percent greater in older adults with hearing problems than in those without, based on results from the Modified Mini-Mental State Exam. A five-point decline on that test is considered a “clinically significant” indicator of a change in cognition.

Using this information, Dr. Lin found that elderly people with hearing problems experienced a five-point decline on the exam in 7.7 years, compared with 10.9 years for those with normal hearing.

Results from the Digit Symbol Substitution Test showed the same downward trend, though not quite as steep: older people with hearing loss recorded a yearly rate of cognitive decline 32 percent greater on it than those with intact hearing. In both cases, the results showed an association only, with no proof of causality.

Still, given the fact that nearly two-thirds of adults age 70 and older have hearing problems, it is an important finding.

For caregivers and older adults, the bottom line is “pay attention to hearing loss,” said Kathleen Pichora-Fuller, a professor of psychology at the University of Toronto who was not involved in the study.

Most people seek medical attention for hearing difficulties 10 to 20 years after they first notice a problem, she said, because “there’s a stigma about hearing loss and people really don’t want to wear a hearing aid.” That means years of struggling with the consequences of impairment, without interventions that can make a difference.

One consequence that may help explain Dr. Lin’s findings is social isolation. When people have a hard time distinguishing what someone is saying to them, as is common in older age, they often stop accepting invitations to dinners or parties, attending concerts or classes, or going to family events. Over time, this social withdrawal can become a self-fulfilling prophecy, leading to the loss of meaningful relationships and activities that keep older people feeling engaged with others.

A substantial body of research by cognitive scientists has established that seniors’ cognitive health depends on exercising both body and brain and remaining socially engaged, and “now we have this intersection of hearing research and cognitive research lining up and showing us that hearing health is part of cognitive health,” said Dr. Pichora-Fuller, who originally trained as an audiologist.

Family physicians and internists, too, often dismiss older patients’ complaints about hearing, and should pay close attention to Dr. Lin’s research, she said.

“I hope this study will be a wake-up call to clinicians that auditory tests need to be part of the battery of tests they employ to look at an older person’s health,” agreed Patricia Tun, an adjunct associate professor of psychology at Brandeis University.

Although the tests are effective and cause no known harm, a panel of experts recently failed to recommend them for older adults because of a lack of supporting evidence, as I wrote last August.

Another potential explanation for Dr. Lin’s new finding lies in a concept known as “cognitive load” that Dr. Tun has explored through her research. Basically, this assumes that “we only have a certain amount of cognitive resources, and if we spend a lot of those resources of processing sensory input coming in — in this case, sound — it’s going to be processed more slowly and understand and remembered less well,” she explained.

In other words, when your brain has to work hard to hear and identify meaningful speech from a jumble of sounds, “you’ll have less mental energy for higher cognitive processing,” Dr. Tun said.

Even seniors who hear sounds relatively well often report that words sound garbled or mumbled, she noted, indicating a deterioration in hearing mechanisms that process complex speech.

Also, as yet unidentified biological or neurological pathways may affect both speech and cognition. Or hearing loss may exacerbate frailty and other medical conditions that older people oftentimes have in ways that are as yet poorly understood, Dr. Lin’s paper notes.

A limitation to his study is its reliance, in part, on the Modified Mini-Mental State exam, which asks older adults to respond to questions posed by an interviewer, according to Barbara Weinstein, a professor and head of the audiology program at CUNY’s Graduate Center.

Her research has shown that hearing-compromised seniors may not understand questions and answer incorrectly, confounding results. Another limitation arises from the failure to test participants’ hearing over time, as happened with cognitive tests, making associations more difficult to tease out.

Dr. Lin hopes to address this through another research project that would follow older adults over time and test whether interventions such as hearing aides help prevent the onset or slow the progression of cognitive decline. In the meantime, older people and caregivers should arrange for hearing tests if they have concerns, and consider getting a hearing aid if problems are confirmed.

Getting sound to the brain is the “first and most important step” in preventing sensory deprivation that can contribute to cognitive dysfunction, said Kelly Tremblay, a professor of speech and hearing science at the University of Washington.