New research suggests that adults with hearing loss may face a higher risk of dementia and perhaps Alzheimer’s disease than those who do not suffer hearing loss. The risk of dementia rises with greater loss of hearing say researchers. The study appears in the February issue of the journal Archives of Neurology.
Study lead author Dr. Luigi Ferrucci, chief of the U.S. National Institute on Aging’s Longitudinal Studies Section, as well as director of the Baltimore Longitudinal Study of Aging said, “This work suggests that there is a strong predictive association between hearing loss as an adult and the likelihood of developing cognitive decline with aging.”
The authors write that by the middle of the century, about 100 million men and women worldwide (about one in 85) will be affected by dementia. They explored the association between hearing loss and dementia focused on 639 men and women between the ages of 36 and 90, none of whom had dementia at the start of the study in 1990. They followed up the participants over four years with cognitive and hearing tests. Thereafter they tracked the subjects till 2008 (for an average of about 12 years) to monitor for signs of dementia and/or Alzheimer’s. At the end of the study 125 study participants were diagnosed with “mild” hearing loss (25 to 40 decibels), while another 53 had “moderate” loss (41 to 70 decibels), and six had “severe” loss (more than 70 decibels). Ultimately, 58 patients were diagnosed with dementia, of which 37 had Alzheimer's disease.
Authors concluded that mild hearing loss was linked to a slight increase in dementia risk, but the risk increased noticeably among those with moderate and severe hearing loss. For participants 60 and older, more than 36 percent of dementia risk was linked to hearing loss, the study said. For every additional loss of 10 decibels of hearing capacity, Alzheimer’s risk appeared to go up by 20 percent, the researchers said.
“Hearing loss may be causally related to dementia, possibly through exhaustion of cognitive reserve, social isolation, environmental deafferentation (interruption or destruction of the afferent connections of nerve cells) or a combination of these pathways…With the increasing number of people with hearing loss, research into the mechanistic pathways linking hearing loss with dementia and the potential of rehabilitative strategies to moderate this association are critically needed,” wrote the researchers.
Talking of the next steps in research the authors believe that if further studies confirm the findings, this could lead to the development of new strategies to try to reduce dementia risk. Ferrucci said, “But as a scientist I cannot yet say that curing hearing loss will prevent dementia… We have now opened a window on this association. But there is still a lot of work to be done before we can be sure there is actually a causal relationship.”
According to Dr. Richard B. Lipton, vice chair of neurology at Albert Einstein College of Medicine in New York City, this was an “interesting” exploration that is predicated on “the widespread notion that chronological age may not be the best measure of biological age.” “Some people have suggested that the most powerful risk factor that we know of for Alzheimer's is age itself,” he noted. “The older you are the more likely you are to develop the disease. And we know that risk doubles every five years after the age of 65…But some 90-year-olds are in nursing homes, while others are on the golf course. So here we have the notion that hearing loss may be a kind of biological, rather than chronological, measure of aging. In other words, an indication that someone is not actually aging all that well,” he said.
“Communication can become very difficult for patients with dementia. In order to set the patient up for success, difficulty with communication should prompt a hearing evaluation,” Dr. Tiffany Chow, a senior clinician-scientist, said.
Dr. Lipton continued, “Another idea is that hearing loss might result from damage to nerve cells…That means damage to the hearing organ and inner ear structure called the cochlea, and the hair cells that pick up the pattern of vibration that the sound produces in the ear. And if there’s damage to the neurons that mediate hearing, that may be a kind of marker for similar damage to nerve cells involved in memory and higher cognition…And then a third possibility is that there’s a lot of evidence that hearing loss is very socially isolating, just as there’s a lot of evidence that cognitive engagement protects against dementia. And that would mean that the loss of cognitive stimulation could itself contribute to the risk for Alzheimer’s.
“Communication can become very difficult for patients with dementia. In order to set the patient up for success, difficulty with communication should prompt a hearing evaluation,” Dr. Tiffany Chow, a senior clinician-scientist, said Tuesday.
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