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Published on: December 29, 2017
by Women’s Brain Health Initiative:
For many of us, hearing loss is considered a typical part of the aging process and no great cause for alarm. However, studies from Johns Hopkins University have discovered links between hearing loss, cognitive decline, and dementia.
“Hearing loss shouldn’t be considered an inconsequential part of aging,” said Dr. Frank Lin, assistant professor at Johns Hopkins and an otologist and epidemiologist who studies the effects of hearing loss on older adults. In one study involving nearly 2,000 men and women between the ages of 75 and 84, Dr. Lin and his colleagues found that over a six-year period, cognitive abilities (including memory and concentration) of those with hearing loss declined 30-40% faster than in individuals with “normal” hearing.
A 2011 study of approximately 600 older adults found that those with hearing loss at the beginning of the study were more likely to develop dementia than adults without hearing loss. In fact, the more severe the hearing loss, the more likely the individuals were to develop dementia. Participants with mild, moderate, and severe hearing loss were, respectively, two, three, and five times more likely to develop dementia than those without hearing impairment.
Another study conducted by Dr. Lin and his colleagues found accelerated rates of brain atrophy in individuals with impaired hearing compared with those who had normal hearing. Additionally, the researchers linked hearing loss to “deep episodes of stress, depression or bad mood,” as well as a heightened risk of hospitalization and an increased risk of falls.
Dr. Richard Gurgel, assistant professor of Otolaryngology – Head and Neck Surgery at University of Utah Health Care, studied more than 4,400 men and women aged 65 and older and found that those with hearing loss at the commencement of the study developed dementia earlier and at a higher rate than those without hearing loss. Dr. Gurgel, Dr. Lin, and other researchers are now focused on determining whether hearing loss may causes dementia or is related to dementia. “Dementia has so many causes. I think hearing loss could be a very important component, but there are certainly a lot of factors that play into dementia,” Dr. Gurgel said.
The first hypothesis that explains why hearing loss may be associated with the development of dementia is referred to as the cognitive load theory. If the brain is constantly coping with degraded sounds, its resources are dedicated to processing those sounds to the detriment of other processes (such as memory and thinking).
The second theory involves brain atrophy. Hearing impairment may directly contribute to accelerated rates of atrophy in parts of the brain that process sound. Those parts of the brain do not work in isolation, according to Dr. Lin; rather, they also “play roles in memory and sensory integration and have been shown to be involved in the early stages of mild cognitive impairment and Alzheimer’s disease.”
The third explanation is social isolation. Individuals who have difficulty hearing often tend to withdraw from society because they find it challenging to communicate with others. Numerous studies have found that a loss of engagement and loneliness are both risk factors for cognitive decline.
Although estimates on the number of individuals suffering from hearing loss vary, the National Institute on Deafness and Other Communication Disorders estimates that nearly 25% of those aged 65 through 74, and as much as 50% of those aged 75 and older, have disabling hearing loss.
Approximately 26 million individuals living in the U.S. between the ages of 20 and 69 have high-frequency hearing loss due to noise exposure. While millions of individuals could benefit from the use of hearing aids, fewer than one in three adults aged 70 and older who suffer from hearing loss use them. Even fewer adults between the ages of 20 and 69 who could benefit from hearing aids use them (approximately 16%).
A new long-term study published in the October 2015 edition of the Journal of the American Geriatric Society showed that wearing hearing aids reduces cognitive decline associated with hearing loss. The study was conducted over a period of 25 years and followed 3,670 men and women, aged 65 and older. The study included three groups of participants: those who did not report hearing loss (considered the control group); those with hearing loss who did not use hearing aids; and those with hearing loss who did use hearing aids. The researchers compared the rate of cognitive decline among these groups and found no difference between the control group and those who used hearing aids, but did find that those with untreated hearing loss had lower scores on a test of cognitive function.
Dr. Gurgel and his colleagues are currently examining whether treating an individual’s hearing loss will improve cognition. Likewise, Dr. Lin and his team are planning a study that they hope will indicate whether the treatment of hearing loss can reduce the risk of dementia. The five-year study will follow 800 older adults and measure cognitive decline. Some participants will receive state-of-the-art hearing treatment, while others will simply receive “wellness advice.” As Dr. Lin explained, if “we look at risk factors for cognitive decline that are modifiable, and hearing loss is one of them, that could be tremendously exciting. [Hearing loss] is really common, and theoretically the treatments we have are no risk. That makes it very exciting as a public health target.”
According to Rex Banks, the Director of Audiology at the Canadian Hearing Society, “[a]ll signs and research are pointing towards hearing aids being a treatment for dementia but we are just not there yet to say that this is definitively true.” Importantly, though, research is ongoing in this area.
In The Lancet July 2017 Commission report titled “Dementia Prevention, Intervention and Care”, nine potentially modifiable health and lifestyle factors were identified from different phases of life that, if eliminated, could prevent dementia. One of these factors is hearing loss. While the recognition of hearing loss as a potential risk is still new, and the research is at an early stage, if hearing loss is eliminated, the Commission estimates a 9% reduction in new dementia cases. Intervention for hearing loss could, in fact, push back the onset of dementia for many people for years.
Source: MIND OVER MATTER – V5
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