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doi: 10.1097/01.HJ.0000396581.29247.fa
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Seniors with high levels of hearing loss are significantly more likely to develop dementia over time than those who retain their hearing, according to a new study by Johns Hopkins University and the National Institute on Aging published in the Archives of Neurology.

The new study, published in the February 2011 issue, focused on 639 people whose hearing and cognitive abilities were tested as part of the Baltimore Longitudinal Study on Aging between 1990 and 1994. The research was supported by the intramural research program of the National Institute on Aging.

While about a quarter of the volunteers had some hearing loss at the start of the study, none had dementia. Researchers also took other dementia risk factors into account, including diabetes, high blood pressure, age, sex, and race.

These volunteers were then closely followed with repeat examinations every one to two years, and by 2008, 58 of them had developed dementia, including 37 who had alzheimer's disease. Participants with hearing loss at the beginning of the study were significantly more likely to develop dementia by the end. Compared with volunteers with normal hearing, those with mild, moderate, and severe hearing loss had twofold, threefold, and fivefold (respectively) the risk of developing dementia over time.

Of the participants, 125 had mild hearing loss (25 to 40 dB), 53 had moderate hearing loss (41 to 70 dB), and six had severe hearing loss (more than 70 decibels).

The risk of dementia was higher in those with hearing loss of greater than 25 decibels, with further increases in risk observed among those with moderate or severe hearing loss as compared with mild hearing loss. For participants age 60 and older, more than one-third of the risk of dementia was associated with hearing loss.

The risk of developing Alzheimer's disease, specifically, also increased with hearing loss, such that for every 10 decibels of hearing loss, the extra risk increased by 20 percent. The results showed no association between self-reported use of hearing aids and a reduction in dementia or Alzheimer's disease risk.

While the reason behind the link remains unknown, investigators believe a common pathology may underlie both, or that the strain of decoding sounds over the years may overwhelm the brains of hearing loss patients, leaving them at higher risk for dementia. Investigators also suggest that hearing loss could lead to dementia by making individuals more socially isolated, which is a known risk factor for various cognitive disorders, including dementia.

“Researchers have looked at what affects hearing loss, but few have looked at how hearing loss affects cognitive brain function,” says study leader Frank Lin, MD, PhD, assistant professor in the Division of Otology at Johns Hopkins University School of Medicine. “There hasn't been much crosstalk between otologists and geriatricians, so it's been unclear whether hearing loss and dementia are related.”

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People with untreated hearing loss could lose as much as $30,000 of their annual income, according to a national study by the Better Hearing Institute (BHI).

Researchers observed more than 40,000 households and found that use of hearing aids reduced the risk of income loss by 90 to 100 percent in those with milder hearing loss, and from 65 to 77 percent in those with severe to moderate hearing loss.

The findings also showed that the loss in income for people with untreated hearing loss due to underemployment is estimated at $176 billion and that there is a strong correlation between the degree of hearing loss and unemployment in those who do not use hearing aids. Those with severe hearing loss showed levels double that of the normal hearing population and nearly double that of patients using hearing aids.

BHI executive director Sergei Kochkin, PhD, makes various suggestions to employers to make an effort to increase awareness and education among employees, including creating an environment where hearing loss is acceptable, and covering hearing aids in corporate insurance plans.

“The real tragedy in delaying hearing loss treatment is that when left unaddressed, hearing loss negatively affects individuals and their families for the rest of their lives in the form of lost wages, lost promotions, lost opportunities, lost retirement income, and unrealized dreams,” Dr. Kochkin said.

“But when people with even mild hearing loss use hearing aids, they improve their job performance, increase their earning potential, enhance their communication skills, improve their professional and interpersonal relationships, stave off depression, and better their quality of life.”

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New research shows that more than 60 percent of American adults over the age of 70 have hearing loss, although those of black race appear to have a protective effect against it.

The study, conducted by Frank Lin, MD, PhD, assistant professor in the Division of Otology at Johns Hopkins University School of Medicine, and colleagues from the National Institute on Aging, was published in the Journal of Gerontology: Medical Sciences.

The researchers analyzed data from the 2005-2006 cycle of the National Health and Nutrition Examination Survey, during which time the hearing of participants over 70 years old was checked using a test that determined whether they could detect tones in frequencies used in speech. These findings are believed to be the first nationally representative survey in older adults on this condition.

After analyzing data from 717 volunteers, the researchers found that about 63 percent had mild to severe hearing loss. Their diverse selection of demographic data also showed that older or male patients were more likely to have hearing loss (even at more severe levels) than younger or female subjects. Additionally, while approximately 64 percent of white patients had hearing loss, only about 43 percent of black subjects did.

Even after accounting for other associated factors such as age and previous noise exposure, black participants were still found to have only a third of the chance of having hearing loss than white participants. Researchers aren't sure why this difference is prevalent, though it has been suggested that pigment produced by cells in the skin and inner ear might protect the inner ear by absorbing free radicals, as well as other mechanisms.

Dr. Lin noted that various studies have linked hearing loss in older adults to other problems, including cognitive decline, dementia, and poorer physical functioning. Although there is a large population of older adults with hearing loss, this study found that only 20 percent use hearing aids.

“There's no doubt [hearing aids] improve communication skills and quality of life,” Dr. Lin said. “But do they improve bigger outcomes, such as cognition and social isolation? We don't really know.”

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Patients suffering from hearing problems that began during infancy and childhood could benefit from a stem cell transplant from the nose, according to recent research published early online in Stem Cells.

The study revealed that mucosa-derived stem cells can help preserve hearing function during the early stages of sensorineural hearing loss.

To study the effects of this treatment, investigators injected nasal stem cells into the cochlea of mice (which have been known to show a similar decline in hearing function after infancy) showing symptoms of hearing loss. They examined patient hearing levels by using the auditory brainstem response assay to determine the hearing threshold.

After comparing these mice to mice who had not received the treatment a month later, it was determined that the threshold was significantly lower in the stem-cell transplanted mice. The study authors noted that a significant challenge in tackling sensorineural hearing loss is the fact that the human cochlea's regenerative ability is very limited.

“These cells can be obtained easily from the nasal cavity, making this transplantation a potential treatment for other human conditions including Parkinson's disease and cardiac infarction,” said lead author Sharon Oleskevich, MD, from the Hearing Research Group at the University of South Wales.

The editors of Stem Cell noted that since the cells did not integrate into the cochlea, the effects from the adult stem cells were attributed to the release of factors to preserve endogenous stem cell function, as mesenchymal stem cells are known to provide factors to promote health and functioning among many types of cells.

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Bone-anchored hearing aids could be beneficial in improving hearing and quality of life in children with hearing loss in one or both ears, according to new research published in the Archives of Otolaryngology – Head & Neck Surgery (2011;137:130-138).

The study was led by Maarten J. F. de Wolf, MD, and colleagues at the Radboud University Nijmegen Medical Centre, in Nijmegen, the Netherlands. Dr. Wolf and colleagues obtained information about 31 children over the age of four who were current bone-anchored hearing aid (BAHA) users for one to four years.

Although BAHAs were commonly fitted in adults when first introduced, overtime they have become a popular option for children with bilateral conductive hearing loss who are too young to undergo alternative surgical procedures.

Of the children in the study, 16 had bilateral hearing loss and 15 had unilateral hearing loss. The study results showed that 12 of the 13 children in the bilateral hearing loss group who used a BAHA for more than eight hours a day said it was worth the effort. In the unilateral hearing loss group, seven used a BAHA for more than eight hours a day, while six used it between four and eight hours a day. In total, 10 children in this group felt the device was worth the effort.

In both subgroups, a younger age at the time of the device fitting was associated with greater benefit and quality of life after extended use, and it was found to have a significant benefit on learning in the bilateral hearing loss group. Although the same benefit was observed in the unilateral hearing group, the researchers recommended that BAHA use in this group should be made on an individual basis.

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New recommendations to routinely assess hearing loss in patients over 50 are effective, according to new findings published in the Annals of Internal Medicine (2011; 15:347-355).

According to the study, led by Roger Chou, MD, of the Oregon Evidence-Based Practice Center at the Oregon Health and Science University, 20 to 40 percent of adults in this age group have diminished hearing, with many failing to notice because of its mild onset and progressive nature. Additionally, 10 to 20 percent of adults with auditory deficits have worn hearing aids.

The U.S. Preventative Task Force first issued these screening recommendations in 1996. In 2009, it began reviewing evidence to revise the screening guidelines, examining randomized trials, controlled observational studies, and research on diagnostic accuracy. Their primary sources for data included Ovid Medline and the Cochrane Systematic Reviews and Central Register of Controlled Trials. Last year's review revealed no harmful effects from screening or hearing aids, but that more research is needed.

The scarcity of evidence for benefits and harms of screening and treatments was stated as a limitation to this study, as were the exclusion of non-English language studies and the inclusion of diagnostic accuracy trials in populations recruited from specialty settings. The authors also noted the need for research in several other areas, including the result of screening in primary care offices, the optimum age at which to begin screening, and the amount of hearing loss that would indicate the use of hearing aids.

“Because the effectiveness of any hearing screening strategy will depend on how likely the persons who might benefit from hearing aids are to actually use them, research is needed on effective methods for enhancing follow-up rates and uptake of recommended treatments (including more effective treatments or increased usability of hearing aids) after screening,” the authors wrote.

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A low-dose, two-drug combination (two from the anti-epilepsy family and two from the glucocorticoid family) that reduces hearing loss in mice before exposure to loud noise, and was later used as a hearing loss treatment, has been found effective.

The study was led by Jianxin Bao, PhD, research associate professor of otolaryngology at the Washington University School of Medicine in St. Louis, and was supported by the National Institute on Deafness and Other Communication Disorders. The researchers presented their work at the meeting of the Association for Research in Otolaryngology in Baltimore. Although the two drugs have been known to protect hearing when used individually, this is the first study to test them together for this indication. The combination has also already been approved by the Food and Drug Administration for other conditions.

In an effort to test each drug's ability to prevent hearing loss, Dr. Bao's group gave various doses to mice two hours before exposing them to noise. They tested the treatment by administering the drugs to different groups of mice 24 hours after noise exposure. Three of the drugs showed increased protection with higher doses, and two of the drugs in combination (the anticonvulsant zonisamide and the glucocorticoid methylprednisolone) showed comparable hearing protection when administered in much lower doses versus being administered alone.

“We found they have synergy,” said Dr. Bao. “Two drugs at lower dosages can block more signaling pathways than one alone, improving results while reducing side effects.”

Although these drugs do not prevent all hearing loss following sustained hearing loss at a noise level of 110 decibels, they can significantly reduce it by about 10 to 30 decibels, which could make a difference in being able to hear everyday speech.

In his group's previous work, Dr. Bao found that anticonvulsant drugs for epilepsy treatment helped protect hearing in mice after exposure to loud noise. Additionally, other groups found that glucocorticoids (anti-inflammatory drugs frequently used to treat allergies and asthma) were also protective.

Although the reasons these drugs aid in reducing noise-induced hearing loss are not well understood, anticonvulsants are known to block calcium channels in nerve cells. Dr. Bao and colleagues suggest that the drug helps protect neuronal connections between hair cells and auditory neurons.

© 2011 Lippincott Williams & Wilkins, Inc.