Clinical and Health Affairs
Hearing Loss and Dementia: New Insights
By Kristi Albers, Au.D.
■ The aging brain is a hot topic among researchers and health professionals worldwide. Although our knowledge of the way the brain changes with age is in its infancy, research into hearing loss and dementia has gained momentum. Recent studies suggest that persons with hearing loss are more likely to develop Alzheimer’s disease or other forms of dementia over time. This article discusses recent findings.
According to the Centers for Disease Control and Prevention (CDC), 37 million adults in the United States had difficulty hearing in 2006.1 This was a substantial increase from 2000, when 31.5 million U.S. adults reported having some form of hearing loss.2 National Institute on Deafness and Other Communication Disorders (NIDCD) data show hearing loss increases with age, with 30% percent of people between the ages of 65 and 74 years and 47% of those 75 years or older reporting some degree of hearing loss.3 Data from the 2010 National Health Survey released in December 2011, show 37% of U.S. adults age 65 and older report hearing loss.4
The exact percentage of people living with hearing loss is somewhat difficult to measure for a number of reasons. Prevalence can differ depending on how hearing loss is defined (ie, if any degree of hearing loss is included), how it is measured (self-report versus objective testing), the age groups included in the data, and other variables. Recent research by a team from Johns Hopkins University reported in the Journal of Gerontology demonstrated that age-related hearing loss, or presbycusis, may be more common than we once thought. The researchers analyzed data from the 2005-2006 cycle of the National Health and Nutrition Examination Study, which is the first to ever include hearing assessments on adults 70 years and older. They found that hearing loss is prevalent in nearly two-thirds of adults aged 70 years and older.5
Another prevalent and growing health concern among older adults is dementia. Data from the first nationally represented population-based study of dementia in the United States, published in 2007, suggest that about 3.4 million Americans age 71 and older (ie, one in seven people in that age group) have some form of dementia and 2.4 million of them have Alzheimer’s disease.6 As the population ages, those numbers are expected to increase. Clinicians and researchers have long been aware that there is a relationship between hearing loss and cognitive decline in older adults. This article discusses that relationship and new findings that suggests that hearing loss is a risk factor for dementia.
Presbycusis and Untreated Hearing Loss
Presbycusis most often starts to affect people in their 60s; it may worsen with age. Age-related hearing loss begins in the higher frequencies and spreads to the mid and low frequencies over time. Typically, the first signs of presbycusis are evident at the highest two frequencies tested, 6000 and 8000 Hz. Examples of sounds affected by hearing loss at such frequencies are birds chirping and the rustling of dry leaves.
When hearing loss begins to affect frequencies between 1000 and 6000 Hz, people begin to notice a change in their ability to hear. These frequencies are important for understanding speech. Persons with presbycusis often will report that they can hear but can’t always understand because of the reduced audibility of consonant sounds. For example, they may not be able to discriminate between words such as “cat” and “sat.”
Hearing professionals have long been aware of the negative effects of untreated hearing loss. Clinical observation has shown that individuals living with untreated hearing loss often experience social isolation. They become afraid to interact with others, as they fear making mistakes in conversation.
In 1999, the National Council on Aging published a landmark study, involving 2,300 individuals with hearing loss who were older than 50 years of age, demonstrating the effects of untreated hearing loss. The study looked at people with untreated hearing loss and at people who had treated their hearing loss with hearing aids. It found that the individuals who used hearing aids reported improvements in many areas including their relationships with friends and family members, self-confidence, social life, and self-esteem.7
In addition to affecting one’s quality of life, untreated hearing loss also may affect a person’s safety. They may fail to hear alarms or important public messages, and they may make mistakes when following directions regarding health-related issues such as wound care, medication use, or adhering post-surgical restrictions. Although accidents or deaths related to hearing loss are not tracked by public agencies, the risks to those with hearing loss are real.
Hearing Loss and Cognitive Function
Recent research suggests that untreated hearing loss may affect a person’s cognitive functioning as well as their quality of life. A study by investigators from Johns Hopkins University and the National Institute on Aging using data from the Baltimore Longitudinal Study on Aging suggests that hearing loss itself is associated with an increased risk of developing dementia.8 The team studied the association between hearing loss and dementia in 639 individuals. The participants, none of whom exhibited signs of dementia at the time they enrolled in the study, underwent audiometric testing between 1990 and 1994. The investigators defined hearing loss by a pure-tone average of hearing thresholds at 0.5, 1, 2, and 4 kHz in the ear with better hearing. Normal hearing was defined as pure-tone thresholds averaging less than 25 dB. Of the 639 individuals tested, 125 had mild hearing loss (thresholds between 25 and 40 dB), 53 had moderate hearing loss (41 to 70 dB thresholds), and six had severe hearing loss (thresholds >70 dB). These same individuals were followed for the development of dementia or Alzheimer’s disease through May 31, 2008. At follow-up, 11.9 years after study participants were first tested, 58 cases of dementia were diagnosed, 37 of which were Alzheimer’s disease. Further analysis of the data showed that as the extent of hearing loss increased so did the risk of developing dementia.
The researchers estimated that more than one-third of the risk for incident all-cause dementia was associated with hearing loss among individuals older than 60 years. They noted, “whether hearing loss is a marker for early-stage dementia or is actually a modifiable risk factor for dementia deserves further study.”8 These findings are consistent with those from previous studies demonstrating an association between hearing loss and dementia. In 1989, a study involving 100 persons with Alzheimer’s-type dementia found hearing loss to be “significantly and independently associated with the severity of cognitive dysfunction.” The authors of that report indicated that the results lent support to the hypothesis that hearing loss may contribute to cognitive dysfunction in older adults.9
Another study conducted in 1996 involved patients receiving treatment at a memory clinic to find out if certain hearing loss screening tools were adequate for determining hearing loss in this population. The population consisted of 52 patients, 30 of whom met the criteria for probable Alzheimer’s disease and 22 of whom met the criteria for other forms of cognitive impairment. Audiometric testing and questionnaires showed 49 of the 52 had significant hearing loss.10 The investigating team found a discrepancy between self-reports and reports by family members regarding hearing loss for the 30 patients with Alzheimer’s disease. For patients with other forms of cognitive impairment, the discrepancy was not as significant. The researchers concluded that because of the high prevalence of hearing loss they observed and the lack of validity of self-reporting of hearing loss for those with Alzheimer’s disease, a hearing assessment should be part of any assessment of cognitive function.10
In a follow-up study of National Health and Nutritional Examination Survey results, the Johns Hopkins group analyzed data from the 1999-2002 cycles, during which participants ages 60 to 69 years underwent audiometric and cognitive testing. In this study, hearing loss was defined by a pure tone average of hearing thresholds at 0.5, 1, 2, and 4 kHz in the ear with better hearing.11 The Digit Symbol Substitution Test (DSST), a nonverbal test that assesses executive function and psychomotor processing, was used to evaluate cognitive functioning. Information on hearing aid use, medical history, and demographics was obtained through interviews. The results indicated greater hearing loss was significantly associated with lower scores on the DSST after adjustments were made for both demographic factors and medical history. In fact, the study’s authors noted that the reduction in cognitive performance associated with mild hearing loss (25 dB thresholds) was equivalent to that associated with someone seven years older than the person tested. In regard to hearing aid use, a positive association was observed in terms of cognitive functioning, meaning persons who reported using hearing aids scored better on the DSST on average.11
The Importance of Screening for Hearing Loss
The prevalence of hearing loss in older people is significant. The new research discussed in this article suggests that hearing loss may put older adults at risk for developing Alzheimer’s disease or other forms of dementia. Additional research is still needed to further examine the relationship between hearing loss and dementia; however, at this time, there is enough evidence to support routinely screening and treating older adults for hearing loss.
A comprehensive hearing evaluation is the gold standard for objectively identifying hearing loss. Given the need for properly calibrated test equipment and a sound-treated space, such testing may not be feasible during routine wellness visits. Standardized screening tools with documented validity are an effective alternative. These are easy to use and quickly determine the need for further evaluation.
The Hearing Health Quick Test is a 15-item questionnaire developed by the American Academy of Audiology.12 (It is available at www.audiology.org.) The test can be administered in the physician’s office by a medical assistant or nurse, or completed independently by the patient in the waiting room. Patients indicate whether or not they encounter difficulty hearing in a variety of situations. Scoring is simple, with a referral for a hearing evaluation warranted if the patient responds “yes” to two or more of the questions. For patients with possible cognitive impairment, it is recommended that the questionnaire be completed with input from a family member or other caregiver, as persons with Alzheimer’s disease have been shown to have poor self-reporting of hearing loss.10
Patients’ also may be screened in the physician’s office with a small, hand-held device that emits pure tones. The nurse or medical assistant places the instrument in the patient’s ear and instructs him or her to respond when a beep is heard. Only a few frequencies are tested—often 1, 2, and 4 kHz—and failure at any frequency warrants a referral for a complete hearing evaluation. For best results, the screening should be performed after an otoscopic exam to rule out the presence of cerumen.
The use of any screening method is better than none at all; however, the combination of screening with pure tones and a questionnaire has been demonstrated to yield the best results.13
Identifying and treating hearing loss sooner rather than later may have far-reaching benefits in terms of reducing the risk for developing Alzheimer’s disease or other forms of dementia and maintaining a good quality of life for older adults. MM
Kristi Albers is a clinical audiologist at Innsbruck Hearing and Balance in New Brighton, Minnesota, and president-elect of the Minnesota Academy of Audiology.
References
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13. Yueh B, Collins MP, Souza PE et al. Long-term effectiveness of screening for hearing loss: The screening for auditory impairment—Which hearing assessment test (SAI-WHAT) randomized clinical trial. J Am Geriatr Soc. 2010;58:427-34.