MONDAY, Jan. 21, 2013 (HealthDay News) -- Seniors who have trouble hearing may see their thinking skills slip away faster than others do, new research suggests.
The study of older U.S. adults found that those with hearing problems were 24 percent more likely to develop mental impairment over six years.
The Johns Hopkins researchers don't know for sure whether hearing loss directly causes mental decline in some cases -- or whether using hearing aids might help. But they are planning to study that possibility.
"At this point, the particular neural mechanisms -- that is, the 'why' and 'how' -- that link hearing loss to dementia are unclear," said Daniel Polley, of the Massachusetts Eye and Ear Infirmary and Harvard Medical School in Boston.
What is clear is that older adults should take hearing problems seriously, noted Polley, who was not involved with the study.
"If there is a takeaway to this, it would be to encourage folks to have their hearing tested by a health professional," Polley said.
The findings, which appear in the Jan. 21 issue of JAMA Internal Medicine, are based on 1,984 adults in their 70s and 80s who showed no signs of impaired memory or thinking at the study's start. But the majority -- 1,162 in all -- did show some hearing loss.
Over the next six years, 609 men and women developed new signs of mental impairment -- based on a standard test of memory, concentration and language skills. And that risk was 24 percent higher among people who had hearing problems.
The researchers estimate that it would take a hearing-impaired older adult just under eight years, on average, to develop mental impairment, versus 11 years for their peers with normal hearing.
None of that proves cause-and-effect. However, the researchers did account for a number of factors that might have explained the link, such as people's education levels, smoking habits and health conditions such as diabetes, high blood pressure and a history of stroke.
There are reasons to believe that hearing loss could directly contribute to declines in brain function, said lead researcher Dr. Frank Lin, an otologist and epidemiologist at Johns Hopkins School of Medicine in Baltimore.
One is the fact that hearing loss can cause older adults to withdraw socially. When it becomes hard to hear what other people are saying, you might avoid going out or feel cut off from those around you, he noted.
"If you can't hear the person across from you at the dinner table, you won't be engaged in the conversation," Lin said.
That matters because a number of past studies have linked such social isolation and "loneliness" to an increased risk of dementia.
Another possibility, Lin said, is that hearing loss forces the brain to devote extra resources to processing the "garbled" signals it's getting from the ears.
"If you're redirecting brain resources to help with hearing," Lin explained, "that probably comes at the expense of something else -- like working memory."
There are a number of ways to help manage hearing loss, including hearing aids and assistive devices such as telephone amplifiers.
The "biggest question" now, according to Lin, is whether treating hearing loss can slow declines in brain function. He and his colleagues are planning a study to look at that question.
Hearing loss is common, affecting up to two-thirds of adults older than 70. But the fact that it's common doesn't mean it's harmless, both Lin and Polley pointed out.
"Hearing loss is more than an inconvenience or a source of embarrassment," Polley said. "Hearing represents a critical portal to conversation, a behavior that connects humans to one another socially and upon which our mental health greatly depends."
Doctors do not routinely screen older adults for hearing loss, so it's up to people to notice symptoms. Some red flags include having trouble hearing when there is background noise or when more than one person is speaking; problems hearing over the phone; and having to habitually ask people to repeat themselves.
But hearing loss also creeps up on people "slowly and insidiously," Lin said. So it might not be you who notices it, but the people around you.
The study was funded by the U.S. National Institutes of Health. Lin is a consultant to Pfizer, which is developing a potential drug for age-related hearing loss, and has served as an unpaid speaker for Cochlear Europe, which makes cochlear implants to treat severe hearing loss.
Learn more about hearing loss from the U.S. National Institute on Deafness and Other Communication Disorders.