Hearing Loss: Extent, Impact, and Research Needs
Hearing loss may develop at any time during the life course. The onset can be sudden or gradual, and one or both ears can be affected. Hearing loss can result from a variety of causes (e.g., trauma, infection, genetic syndromes, aging, or excessive noise exposure), and the pathological changes may occur in one or more regions of the auditory system. Although some hearing loss might be temporary or treatable using medical or surgical methods, most hearing loss in adults is permanent or slowly progressive. When evaluating the burden of hearing loss in a population, it is important to recognize the heterogeneity in the nature and severity of hearing loss. Individuals also vary in the extent to which auditory rehabilitation, hearing aids, and hearing assistive technologies can improve their communication function (see Chapters 3 and 4). Lessening the effects of hearing loss and improving health and function are the goals of this report’s discussions. This chapter begins with an overview of data on the incidence and prevalence of hearing loss in adults and a discussion of the factors associated with the risk for hearing loss in adults and methods for prevention. Subsequent sections discuss the impact of hearing loss on individuals, their families, and society. The chapter ends with the committee’s recommendations for next steps in this area.
To develop a full understanding of the public health burden of hearing loss in adults in the United States, the committee gathered information from multiple sources in order to determine the extent to which the U.S. population is affected by hearing loss and the impact of those losses. The committee conducted extensive literature searches, with a focus primarily on articles that relied on audiometric measures of hearing; studies using self-
report were included only when they were deemed essential. Cross-sectional epidemiological studies that measure the sensitivity of the auditory system at only one point in time rarely distinguish the pattern of onset or subtype of hearing loss. Because childhood onset of hearing loss as well as most types of acquired hearing loss in adolescence and the early adult years are relatively rare, and because the most common type of hearing loss among aging adults is a slowly developing, symmetrical sensorineural hearing loss called age-related hearing loss or presbycusis, population-based cohorts primarily focus on age-related hearing loss.
DISTRIBUTION OF HEARING LOSS
Studies examining the incidence and prevalence of hearing loss include those that track a number of health outcomes in a cohort (e.g., the Framingham Heart Study, Baltimore Longitudinal Study of Aging) and a few population-based studies that are focused on hearing (e.g., Blue Mountains Hearing Study, Epidemiology of Hearing Loss Study) (see Box 2-1). Information on the extent of hearing loss in military personnel and veterans has been explored in several recent Institute of Medicine reports (IOM, 2006, 2014).
Incidence of Hearing Loss
In addition to providing estimates of the risk of developing a disorder, studies of incidence measure the relative risk associated with such characteristics as age, sex, and race as well as potentially modifiable exposures and other factors that may add prospective evidence for identifying causal pathways. The few studies that have measured the incidence of hearing loss are summarized in Table 2-1. Study designs and methods varied across studies, with only two of the cohorts using traditional population-based designs (Cruickshanks et al., 2003, 2010a, 2015b; Mitchell et al., 2011) and one (Fischer et al., 2015) based on the offspring of one of the population-based cohorts. The other studies employed selection criteria at baseline that may have resulted in a healthier than average sample (Brant and Fozard, 1990; Brant et al., 1996; Gates and Cooper, 1991; Gates et al., 1990; Mościcki et al., 1985) or used very small samples not intended to be representative of the general population of adults (Davis et al., 1990). All but the Baltimore Longitudinal Study of Aging (BLSA), which used Békésy audiometry (a form of automated audiometry), used traditional audiometric assessments of hearing thresholds. The definitions of hearing loss cases varied slightly by frequencies included in the pure tone average. They also differed in that some required bilateral hearing loss (defined by hearing loss in both ears based on the better ear) while others (using the hearing in the worse ear to define cases) included unilateral and bilateral cases. The length of follow-up time varied from 2 to 15 years, with most reporting 5-year event rates. The Epidemiology of Hearing Loss Study (Cruickshanks et al., 2003) and the Beaver Dam Offspring Study (Fischer et al., 2015) cohorts had predominately non-Hispanic white participants. Other cohorts did not report the race/ethnic distributions of their samples, and no data were presented stratifying on race/ethnicity, which suggests, given the demographics of their catchment areas, that the majority of participants also were non-Hispanic white. The committee is not aware of any other published reports of the incidence of hearing loss measured by audiometry in minority populations in the United States.
The reported incidence rates, standardized to annual rates per 1,000 individuals (see Table 2-1), vary from 12 per 1,000 individuals per year in Great Britain to 42.8 per 1,000 individuals per year in Beaver Dam, Wisconsin, and were higher in studies focused on middle-aged and older adults and lower in studies that included younger adults or excluded less healthy participants. The Blue Mountains cohort in Australia was designed to be comparable to the Beaver Dam cohort, and the incidence rates appear remarkably similar when comparing rates using the same pure tone average definition (42.2 per 1,000 individuals per year in the Blue Mountain Hearing Study and 42.8 per 1,000 individuals per year in the Epidemiology of Hearing Loss Study) (Cruickshanks et al., 2003; Mitchell et al., 2011).
However, these comparisons are limited, as no adjustments have been made across cohorts for the actual age and sex distributions of the participants. Nonetheless, the risk of hearing loss was high in all studies of older adults, as can be seen in Table 2-1. Comparing these rates to those for cardiovascular disease (34.6/1,000/year for men and 20.0/1,000/year for women ages 65 to 74 years in the Framingham Heart Study) (NHLBI, 2006), diabetes (7.8/1,000/year) (CDC, 2014), and cancer (4.548/1,000/year) (NCI, 2016) reveals that the risk of hearing loss is up to 2-fold higher than the risk of cardiovascular disease, approximately 5-fold higher than the risk of diabetes, and about 10-fold higher than the risk of cancer. The risk of bilateral hearing loss is approximately 7-fold higher than the risk of bilateral vision impairment (Klein et al., 2001).
Age and Sex
Figure 2-1 shows the age- and sex-specific 5-year incidence of hearing loss in either ear from the Epidemiology of Hearing Loss Study and for bilateral hearing loss in the Blue Mountains Hearing Study (Cruickshanks et al., 2003; Mitchell et al., 2011). Among non-Hispanic white participants in these studies, the incidence of hearing loss was higher at older ages and, within each age group in the Epidemiology of Hearing Loss Study, higher among men than among women. The data on the 80-years-and-older groups have broader confidence intervals because there were fewer participants who did not have hearing loss at baseline and who did have follow-up data.
Although incidence data are scarce and limited to non-Hispanic white populations, the data suggest that the risk of hearing loss increases across the life span and throughout older age and that men have a higher risk of hearing loss than women do. Based on the Epidemiology of Hearing Loss Study data, 18 percent of women aged 60–69 and 35 percent of men aged 60–69 developed hearing loss within 5 years (Cruickshanks et al., 2003).
By 15 years of follow-up, when the participants were 75–84 years of age, 71 percent of the women and 84 percent of the men had developed hearing loss (Cruickshanks et al., 2015b). In models that adjusted for age and sex, the risk of hearing loss nearly doubled with every 5 years of age (hazard ratio [HR] = 1.90, 95 percent confidence interval [CI] = 1.79, 2.02), and men were more than twice as likely as women to develop hearing loss during 15 years of follow-up (HR = 2.23, 95 percent CI = 1.86, 2.66) (Cruickshanks et al., 2015b).
Prevalence of Hearing Loss
In contrast to the limited data on the incidence of hearing loss, numerous cross-sectional studies have described the prevalence of hearing loss.
Selected Studies of Incidence of Hearing Loss
|Study and Number of Participants||Definition of Hearing Loss and Participant Age Range at Baseline||Follow-Up Time||Percent Who Developed Hearing Loss During the Follow-Up Time||Estimated Rate per 1,000 Individuals/Year|
|Framingham Heart Study N = 1,475a (Gates and Cooper, 1991)||PTA of 0.5, 1, and 2 kHz > 26 dB HL Age of participants: 58–88 years||6 years||8.4 (right ear) 13.7 (left ear)||NA|
|Longitudinal Study of Hearing Great Britain: N = 404 Denmark: N = 157 (Davis et al., 1990)||PTA of 0.5, 1, 2, and 4 kHz > 25 dB HL in better ear Age of participants: Great Britain: 40–65 years; Denmark: 49–69 years||Great Britain: 2 years; Denmark: 3 years||Great Britain: 2.4 Denmark: 6.9||Great Britain: 12 Denmark: 23|
|Baltimore Longitudinal Study of Aging N = 531 men (Brant et al., 1996)||PTA of 0.5, 1, 2, and 3 kHz ≥ 30 dB HL in either ear (using Békésy audiometry) Age of participants > 25 years||5.1 to 11.2 yearsb||8.7||NA|
|Epidemiology of Hearing Loss Study N = 1,678c (Cruickshanks et al., 2003, 2010a, 2015b)||PTA of 0.5, 1, 2, and 4 kHz > 25 dB HL in either ear Age of participants: 48–92 years||5, 10, or 15 years||5 years: 21.4 10 years: 37.2 15 years: 56.8||5 years: 42.8 10 years: 37.2 15 years: 37.9|
|Blue Mountains Hearing Study N = 870 (Mitchell et al., 2011)||PTA of 0.5, 1, 2, and 4 kHz > 25 dB HL in better ear PTA of 0.5, 1, 2, and 4 kHz > 25 dB HL in worse ear Age of participants: > 49 years||5 years||17.9 21.1||35.8 42.2|
|Beaver Dam Offspring Study N = 1,984d (Fischer et al., 2015)||PTA of 0.5, 1, 2, and 4 kHz > 25 dB HL in either ear Age of participants: 21–79 years||5 years||8.3||16.6|
NOTE: dB = decibel (measure of sound intensity or volume); db HL = decibels hearing level; kHz = kilohertz (measure of frequency of sound waves); N = number of participants without hearing loss at baseline; NA = not available; PTA = pure tone average.
aNumber of individuals followed for progression of hearing decline.
bFollow-up times varied by age: < 50 years = mean of 10.9 years; 50–59.9 = mean of 11.2 years; 60–69.9 = mean of 7.8 years; ≥ 70 = mean of 5.1 years.
cAt baseline, 1,925 individuals had normal hearing. Over the course of the study, 1,678 individuals participated in at least one follow-up examination (1,636 participated in the 5-year follow-up, 1,465 at 10 years, and 1,240 at 15 years).
dNumber of participants who had 5-year follow-up audiometric testing. Number of participants without hearing loss at baseline = 2,436.
Several large cohort studies carried out in the United States are summarized in Table 2-2. Direct comparisons of the prevalence rates are problematic because of the differences in the age and sex distributions across cohorts. Data from the National Health and Nutrition Examination Survey (NHANES) show that the prevalence of hearing loss rises steeply with age, as shown in Figure 2-2, from 3 percent among adults 20–29 years of age to 49 percent among adults 60–69 years of age (Agrawal et al., 2008). When adults of ages 70 years and older were tested in a more recent wave of NHANES, the prevalence of bilateral hearing loss was found to be 45.6 percent among the 70- to 74-year age group and 80.6 percent in the 85-years-and-older age group (Lin et al., 2011c). These data likely underestimate the true population prevalence since NHANES does not include people living in assisted care facilities, group homes, or nursing homes or those unable to come to the mobile examination center. Insufficient numbers of people from some minority groups and the oldest old are included to produce robust estimates of the prevalence of hearing loss in these subgroups of the population. Using NHANES data, Agrawal and colleagues estimated that 29 million adults ages 20–69 years in the United States have hearing loss, and Lin and colleagues estimated that 30 million people ages 12 and older
Selected Studies of Prevalence of Hearing Loss
|Study, Number, Sex, and Age of Participants||Definition of Hearing Loss||Percent with Hearing Loss (%)|
|Framingham Heart Study
N = 2,293; 40.8% men
Age of participants: 57–89 years (Mościcki et al., 1985)
|PTA of 0.5, 1, and 2 kHz > 20 dB HL in better ear||35|
|PTA of 0.5, 1, and 2 kHz > 20 dB HL in worse ear||53|
|PTA of 0.5, 1, and 2 kHz ≥ 25 dB HL in better ear||31|
|PTA 0.5,1,2,3 > 25 dB HL in better ear||36|
|PTA 0.5,1,2,4 > 25 dB HL in better ear||47|
|Framingham Heart Study
N = 1,662; 40.7% men
Age of participants: 63–95 years (Gates et al., 1990)
|PTA of 0.5 to 4 kHz > 26 dB HL in better ear||29|
|Hispanic Health and Nutrition Examination Survey
N = 2,751; % men not reported
Age of participants: 20–74 years (Lee et al., 1991)
|PTA of 0.5, 1, and 2 kHz > 25 dB HL in either ear||Age-, sex-, and ethnic-background-specific rates varied from 2.3 to 48.1|
|Epidemiology of Hearing Loss Study
N = 3,753; 42.3% men
Age of participants: 48–92 years (Cruickshanks et al., 1998)
|PTA of 0.5, 1, 2, and 4 kHz > 25 dB HL in worse ear||45.9|
|Health, Aging, and Body Composition Study (Health ABC)
N = 2,052; 47.3% men
Age of participants: 73–84 years (Helzner et al., 2005)
|Low-frequency: PTA of 0.5, 1, and 2 kHz > 25 dB HL||59.9|
|High-frequency: PTA of 2, 4, and 8 kHz > 40 dB HL||76.9|
|National Health and Nutrition Examination Survey (NHANES)
N = 5,742; 46.6% men
Age of participants: 20–69 years (Agrawal et al., 2008)
|PTA of 0.5, 1, 2, and 4 kHz > 25 dB HL in either ear||16|
|High-frequency: PTA of 3, 4, and 6 kHz > 25 dB HL in one or both ears||32|
1971–1973: N = 3,192; 47.3% men 1999–2004: N = 4,486; 49.1% men
Age of participants: 25–69 years (Cheng et al., 2009)
|PTA of 1, 2, 3, and 4 kHz > 25 dB HL in worse ear||1971–1973: 28.5
N = 717; % men not reported
Age of participants: over 70 years (Lin et al., 2011c)
|PTA of 0.5, 1, and 2 kHz > 25 dB HL in better ear||44.8|
|Speech frequency PTA (0.5, 1, 2, and 4 kHz) in better ear||63.1|
|Study, Number, Sex, and Age of Participants||Definition of Hearing Loss||Percent with Hearing Loss (%)|
2005–2008: N = 3,143; 2001–2004: N = 3,630; 2005–2006: N = 717; % men not reported
Age of participants: over 12 years (Lin et al., 2011b)
|PTA of 0.5, 1, 2, and 4 kHz > 25 dB HL in better or either ear||Better ear: 12.7
Either ear: 20.3
|Beaver Dam Offspring Study
N = 2,837; 45.6% men
Age of participants: 21–84 years (Nash et al., 2011)
|PTA of 0.5, 1, 2, and 4 kHz > 25 dB HL in worse ear||14.1|
|Hispanic Community Health Study/Study of Latinos 2008–2011
N = 16,415; 47.97% men
Age of participants: 18–74 years (Cruickshanks et al., 2015a)
|PTA of 0.5, 1, 2, and 4 kHz > 25 dB HL in better ear; worse ear||Better ear: 8.24
Worse ear: 15.06
NOTE: dB = decibel (measure of sound intensity or volume); dB HL = decibels hearing level; kHz = kilohertz (measure of frequency of sound waves); PTA = pure tone average.
have bilateral hearing loss and 48 million people have poor hearing in at least one ear (Agrawal et al., 2008; Lin et al., 2011c).
In the Epidemiology of Hearing Loss Study cohort, conductive hearing losses were present in 8 percent of participants, with 0.2 percent having a history of otosclerosis (an uncommon but disabling form of hereditary hearing loss that can be aggravated by pregnancy, becomes disabling in mid-life, and in older age is functionally complicated by presbycusis) and 1.9 percent reporting having had an onset of hearing loss before age 20 years (Cruickshanks et al., 1998). Most participants with hearing loss had bilateral symmetrical losses, which is consistent with the predominant type among adults being a sensorineural hearing loss acquired in adulthood.
The studies described above use a clinically significant cutpoint for defining hearing loss that includes mild losses (26–40 dB HL) as well as moderate and severe or profound losses. The severity of the loss may affect hearing health care needs in various important ways. For example, older adults with profound hearing loss may be candidates for cochlear implants, but this surgical intervention would not be appropriate for someone with a mild loss. Therefore, the committee searched for population-based estimates of the prevalence of hearing loss that were stratified by severity. Cheng and colleagues reported the age–sex–race standardized prevalence of hearing loss by severity in adults 20–69 years of age using data from NHANES I (1971–1973) and NHANES 1999–2004 (Cheng et al., 2009). As shown in Table 2-3, the majority of people with hearing loss had a mild loss, and severe or profound losses were rare in the age range studied, which had an upper limit of 69 years. The Blue Mountains Hearing Study
Age–Sex–Race Standardized Prevalence of Hearing Loss by Severity: Ages 20 to 69 Years
|NHANES I (%)||NHANES 1999–2004 (%)|
|Normal (< 26 dB)||73.5||78.4|
|Mild (26–40 dB)||17.3||13.9|
|Moderate (41–70 dB)||7.8||7.3|
|Severe or profound (71+ dB)||1.3||0.5|
NOTE: dB = decibel; NHANES = National Health and Nutrition Examination Survey.
SOURCE: Cheng et al., 2009.
also reported that the severity of hearing loss increased with age although mild hearing loss was the most common level except in the oldest age group of 85 years and older (Mitchell et al., 2011). Cluster analyses of NHANES data and data from a rural health study described significant variation and gender differences in the shapes of audiogram profiles which may be a useful approach to classifying severity (Ciletti and Flamme, 2008).
Race and Ethnicity
Racial and ethnic differences in the prevalence of hearing loss have been examined in several cross-sectional studies. In the 1999–2004 NHANES, the prevalence of hearing loss among adults 20–69 years was found to be 50 to 60 percent lower among African American participants than among non-Hispanic white participants, and the prevalence among Mexican American participants was similar to that of non-Hispanic white participants (Agrawal et al., 2008). Among older adults (70 years of age or older), this pattern persisted, with non-Hispanic black participants having a lower prevalence than non-Hispanic white participants (Lin et al., 2011c). Similar results were found in the Health, Aging and Body Composition (Health ABC) study (Helzner et al., 2005). In this study of Medicare beneficiaries in two communities (Pittsburgh, Pennsylvania, and Memphis, Tennessee), hearing was tested at the 5-year follow-up visit. Using a pure tone average of 0.5–2 kHz > 25 dB HL cutpoint, they found that the prevalence of hearing loss was 20 to 60 percent higher among white participants than among black participants (Helzner et al., 2005).
In 1982–1984 the Hispanic Health and Nutrition Examination Survey was launched to measure the health of a representative sample of Mexican Americans from the southwestern United States, Cuban Americans from the Miami, Florida, area, and Puerto Ricans from New York City (Lee et al., 1991). Hearing loss (pure tone average 0.5–1, 2 kHz > 25 dB HL either ear) was common in all three groups, but the prevalence was lower among the Puerto Ricans than among the Mexican Americans or the Cuban Americans. More recently, the prevalence of hearing loss was measured in a diverse Hispanic/Latino population as part of the Hispanic Community Health Study/Study of Latinos (Cruickshanks et al., 2015a). In this population-based study in four communities (Bronx, New York; Chicago, Illinois; Miami, Florida; and San Diego, California), hearing loss was common among older adults, and the prevalence was higher among participants with Puerto Rican background than among those with a Mexican background. The prevalence of hearing loss among participants reporting Dominican, Central American, Cuban, South American, or other backgrounds was similar to the prevalence of hearing loss among those with a Mexican background. The report did not include direct comparisons
between Hispanic/Latino participants and non-Hispanic white participants. The limited data suggest that there may be a racial/ethnic variation in the prevalence of hearing loss, although the causes and the effects of this difference on individuals’ function and activities are not known.
Temporal Population Patterns
A few studies have examined changes in hearing loss prevalence over time in the United States. The evidence from these examinations of temporal trends, secular changes, and birth cohort effects suggests that some cases of hearing loss may be preventable since genetic changes would be expected to accrue quite slowly. Modifiable exposures or risk factors are the more likely explanation for rapid shifts in the risk of developing chronic diseases. Although there are no published longitudinal studies of hearing loss incidence over time, data from the 1971–1973 NHANES and 1999–2004 NHANES suggest that the prevalence of hearing loss (pure tone average 1, 2, 3, 4 kHz) declined 4.8 percent between these two time periods, even after adjusting for age, sex, and race (Cheng et al., 2009).
A strong birth cohort effect was found using data from the Epidemiology of Hearing Loss Study cohort and their offspring (Beaver Dam Offspring Study) (Zhan et al., 2010). In each generation (defined as a 20-year period of births) the odds of hearing loss were about 50 percent lower for men and 24 percent lower for women than in the previous generation (Zhan et al., 2010). Similar results were found using early National Health Examination Survey data from 1959–1962 and NHANES data from 1999–2004 (Hoffman et al., 2010). In this paper, the odds of hearing loss among 25–64-year-olds were reported to be about 44 percent lower among men and 34 percent lower among women in the second time period compared to the first. A second report by this group used national data for older adults (64–74 years of age) from 1959–1962 and 1999–2006 (Hoffman et al., 2012). This study found that the prevalence of hearing loss among older adults declined about 25 percent between the first time period and the second. The reasons for these declines are not known, but the findings are consistent with the possibility that adult-onset hearing loss is at least partially preventable or that the rate of loss may be slowed or the onset postponed. Whether the trend will continue remains to be seen. Longitudinal data are not yet available on the impact of current listening patterns (e.g., listening to loud music using ear buds).
Progression of Hearing Loss
Several large longitudinal studies have examined the change in hearing thresholds over time. In the Baltimore Longitudinal Study of Aging, it was
noted that the rates of change were faster at older ages (Brant and Fozard, 1990). Gates and Cooper (1991) reported that 4 percent of Framingham Heart Study participants experienced a significant decline in hearing during a 6-year follow-up period. Lee and colleagues (2005) followed participants for 3 to 11 years with an average of 10 visits and found that thresholds changed by 0.7–1.2 dB HL per year, depending on the frequency. The rates of change were similar in the population-based Epidemiology of Hearing Loss Study, which tested participants only at 5-year intervals (Wiley et al., 2008). Among participants in that study who had hearing loss at baseline, 53 percent experienced a decline in hearing (> 5 dB HL change in pure tone average) in 5 years. Taken together, these data indicate that hearing diminishes gradually over time, although at an accelerating rate with advancing age. Many, although not all, adults over 80 years of age have some degree of hearing loss (see Figure 2-3). This finding has important implications for hearing health care, as individual needs for amplification and other auditory interventions are likely to change over time and the prevalence of that need will increase as the proportion of the population over 80 years of age increases. Additionally, the surge of older Americans caused by the aging of the boomer cohort raises concerns about the aggregate demands for hearing health care. The slow gradual changes also can mean that adults may not
recognize the deterioration in their hearing and may delay seeking help. More research is needed on the best approaches for improving awareness of gradual hearing loss.
HEARING LOSS: CAUSES AND RISK FACTORS
The complexity of the physiologic and neural mechanisms that under-gird hearing and communication in combination with the numerous genetic and environmental factors that can be associated with or the cause of hearing loss makes it a challenging area for research and one in which much remains to be learned. The major causes and risk factors for hearing loss fall into two major categories, congenital and acquired, although there are complex overlaps between the two, including the potential contributions of genetic susceptibilities to certain risk factors.
Congenital and Genetic Hearing Loss
An estimated 2 to 3 of every 1,000 newborn babies in the United States has hearing loss; of those cases, an estimated 50 to 60 percent result from genetic causes (Alford et al., 2014; Kochhar et al., 2007; Mahboubi et al., 2012). More than 100 genes have been identified as having some effect on hearing ability (i.e., nonsyndromic); in addition, more than 400 genetic syndromes result in other clinical abnormalities that may affect hearing ability (Alford et al., 2014; Kochhar et al., 2007). Newborn hearing screening is the standard of care in the United States and in many other countries; in 2013, the Centers for Disease Control and Prevention (CDC) reported that more than 97 percent of newborns in the United States were screened for hearing loss (CDC, 2015a).
The type and degree of hearing loss that appears in newborns vary. Autosomal recessive hearing loss often results from mutations of the GJB2 gene (estimated as 20 percent of all congenital hearing loss), with variations in severity of hearing loss, but individuals often have nonprogressive, severe hearing loss that manifests early in life, usually prelingual (Mahboubi et al., 2012; Venkatesh et al., 2015). The three genes commonly associated with autosomal dominant causes of hearing loss are WFS1, MYO7A, and COCH. WFS1 mutations, for example, affect hearing at high frequencies, while hearing remains normal in the low frequencies (Mahboubi et al., 2012; Venkatesh et al., 2015). For those with mutations in the MYO7A gene, hearing loss is gradual and progressive and manifests in the first 10 years of life. For those with mutations in the COCH gene, hearing loss begins in the 20s, and while the progression is variable, complete deafness often occurs 20 to 30 years later (Mahboubi et al., 2012; Venkatesh et al., 2015).
Acquired Hearing Loss
As noted in Chapter 1, acquired hearing loss may be sudden or gradual in onset and may be caused by any of a number of exposures, diseases, or health conditions, including meningitis; measles and mumps; otosclerosis (progressive fusion of the ossicles of the middle ear); chronic ear infections; autoimmune or inflammatory disorders; fluid or infection in the ear (otitis media); tympanic membrane (ear drum) thickening or perforations; the use of some antibiotic, antimalarial, or cancer chemotherapeutic medications; some head injuries or other trauma; long-term exposure to excessive noise; cerumen (ear wax) or foreign bodies blocking the ear canal; and aging (presbycusis) (WHO, 2015).
Noise-Induced Hearing Loss
One type of acquired hearing loss is noise-induced hearing loss. Long-term exposure to loud and excessive noise may result in temporary increases in thresholds, or “temporary threshold shifts” (the threshold is the quietest sound that can be heard), and may or may not result in permanent changes in hearing, depending on the level of noise and the length of exposure. Acoustic trauma may result from explosive or impulse noise, with blasts at high intensity levels (~180 dB sound pressure level [SPL]) having the potential to cause hemorrhages, perforation of the ear drum, or impacts on the cochlea (IOM, 2006). As noted in two previous Institute of Medicine reports that reviewed noise exposure data in the context of military service (IOM, 2006, 2014), there are few high-quality prospective studies to quantify the risks associated with these exposures. Most studies of noise in humans have been in occupational cohorts (primarily among men), and few have controlled analyses for factors other than noise or age. One recent report from the Millennium Cohort Study of veterans demonstrated that deployment to combat zones, proximity to improvised explosive devices, and combat-related head injuries were associated with new-onset hearing loss (Wells et al., 2015).
Occupational exposure to noise is regulated in the United States by the Occupational Safety and Health Administration. The National Institute for Occupational Safety and Health (NIOSH) has set recommended occupational exposure limits of 85 dB SPL for an 8-hour time-weighted average (NIOSH, 2015b) and recommends the use of hearing protection measures at higher sound levels. In addition to ear muffs, ear plugs, and other personal hearing protection, workplaces with high noise levels can use environmental (e.g., sound walls or the isolation of loud machinery) and administrative controls (e.g, reduced time worked in noisy environments or increased distance from noise) to reduce exposures (OSHA, 2016). NIOSH
estimates that between 5 and 30 million workers in the United States are exposed to occupational noise that puts them at risk for hearing loss, with an additional 9 million potentially at risk due to exposure to ototoxic chemicals, such as certain solvents (Fuente et al., 2013; NIOSH, 2015a). A 30-year review of hearing loss data found that the risk of hearing loss may be declining across occupational groups in many industries (Masterson et al., 2015).
The relationship between noise exposure and the incidence of age-related hearing loss is difficult to determine, particularly as most age-related hearing loss affects hearing ability at high frequencies. Several studies have found that a history of noise exposure was not associated with the rate of later declines in hearing acuity (Lee et al., 2005) or the incidence of hearing loss (Cruickshanks et al., 2003, 2010a; Fischer et al., 2015; Mitchell et al., 2011), even in analyses restricted to those currently employed (Cruickshanks et al., 2010a).
In non-occupational, recreational, and home settings, the levels of noise and lengths of exposure vary widely. Distance from the source of the sound is a factor, as is the volume of the sound and the length of continuous exposure. Target shooting and hunting have been associated with acute onset of hearing loss. Other activities with high and often sustained noise levels that may increase risk for hearing loss include listening to music or other sounds at high volume (including through earbuds or headphones that act to increase the proximity to the source of the sound), participating in a music band, attending loud concerts, and using lawnmowers, leaf blowers, or other high-noise tools (NIDCD, 2014). Ongoing research efforts by the National Institute on Deafness and Other Communication Disorders, the Department of Veterans Affairs, the Department of Defense, and many others are examining noise-induced hearing loss and its etiology and treatment (DoD Hearing Center of Excellence, 2016; NIDCD, 2014; VA, 2015).
Reducing time spent in noisy environments and wearing hearing protection to reduce noise exposure to the ear may help prevent noise-induced hearing loss. Much can be done to alleviate background noises and to promote acoustic environments that have widespread benefit for communication (see Chapter 6).
Risk Factors for Age-Related Hearing Loss
The most common form of acquired hearing loss and the focus of the previously reviewed epidemiological studies is age-related hearing loss. Numerous lifestyle factors, cardiovascular risk factors (including diabetes), medications, neurotoxins, and other factors have been found to be associated with the prevalence of hearing loss (Agrawal et al., 2009; Cruickshanks et al., 2015a; Helzner et al., 2011; Nash et al., 2011). This section focuses on
the results of longitudinal studies that have tested associations with the incidence of audiometrically measured hearing loss or with longitudinal changes in hearing thresholds. Although cross-sectional associations are useful for generating new hypotheses, they are considered weak evidence for potential causal mechanisms and prevention. Observational longitudinal studies have the advantage of providing evidence about exposures that precede the development of the disorder but are not sufficient for determining causal pathways. The strongest evidence would come from randomized controlled trials, a study design that has been rarely used in hearing research.
Indicators of higher socioeconomic status such as higher levels of education or professional occupational categories have been found to be associated with a lower risk of incident hearing loss (or rate of decline) in many (Cruickshanks et al., 2003, 2010a, 2015b; Fischer et al., 2015; Linssen et al., 2014; Mitchell et al., 2011) but not all prospective studies (Kiely et al., 2012). Generational differences in educational attainment explained part of the birth cohort effect on the prevalence of hearing loss discussed above; the impact of birth year was attenuated, although it remained significant (Zhan et al., 2011). This protective pattern is similar to many other disorders of aging, where more highly educated, wealthier people have lower risk of disease, most likely due to a number of factors, but the full reasons are unclear.
No longitudinal cohort studies have reported significant associations between alcohol consumption and a risk of hearing loss (Brant et al., 1996; Cruickshanks et al., 2015b; Fischer et al., 2015; Gopinath et al., 2010a). One study found that current smokers had a 31 percent increased risk of developing hearing loss during 15 years of follow-up (Cruickshanks et al., 2015b). The risk for former smokers who had stopped 5 or more years earlier was similar to those who had never smoked. Cigarette smoking was not associated with 5- or 10-year risk of developing a hearing loss in this cohort, suggesting that the effects accrue slowly. Consistent with this hypothesis, other longitudinal studies with only 5 years of follow-up have not found significant associations between smoking and risk of hearing loss (Fischer et al., 2015; Gopinath et al., 2010a; Kiely et al., 2012). The Baltimore Longitudinal Study of Aging involving 531 men also found no association between smoking and a risk of incident hearing loss (Brant et al., 1996).
Few dietary factors have been identified as being associated with the risk of hearing loss. In the Blue Mountains Hearing Study, people who
consumed fish two or more times per week were 20 percent less likely to develop hearing loss in 5 years of follow-up than those who ate fish less than once a week (Gopinath et al., 2010b). The Nurses’ Health Study II found lower risk of self-reported hearing loss among women consuming more fish and long-chain omega-3 polyunsaturated fatty acids (Curhan et al., 2014).
Blood pressure Population-based longitudinal cohort studies have found no association between blood pressure or hypertension and the risk of hearing loss (Cruickshanks et al., 2015b; Fischer et al., 2015). However, higher systolic blood pressure was found to be associated with hearing loss in the generally healthier Baltimore Longitudinal Study of Aging cohort (Brant et al., 1996). Hypertension was also associated with a faster decline in hearing acuity in a study of Australian participants (Kiely et al., 2012).
Obesity and central adiposity Several longitudinal studies have found obesity or waist circumference—a well-known marker of central adiposity as well as of insulin resistance and cardiovascular risk—to be associated with increased risk of hearing loss (Cruickshanks et al., 2015b; Curhan et al., 2013; Fischer et al., 2015; Linssen et al., 2014). The Maastricht Aging Study reported that a large waist circumference in younger adults and obesity in older adults showed some association with faster deterioration in hearing (Linssen et al., 2014). In the Epidemiology of Hearing Loss Study, there was an 8 percent increased risk of hearing loss for every additional 10 centimeters of waist circumference (Cruickshanks et al., 2015b). Body mass index was significantly associated with a higher (2 percent for every kg/m2) 5-year risk of hearing loss in the Beaver Dam Offspring Study (Fischer et al., 2015). In the Nurses’ Health Study II, body mass index and larger waist circumference were associated with a risk of self-reported hearing loss (Curhan et al., 2013).
Diabetes Although there have been numerous cross-sectional studies reporting a higher prevalence of hearing loss among people with diabetes (Agrawal et al., 2009; Cruickshanks et al., 2010b, 2015a; Helzner et al., 2011; Mitchell et al., 2009), there has been little evidence from longitudinal studies. Diabetes was not associated with incidence of hearing loss in several studies (Cruickshanks et al., 2015b; Fischer et al., 2015; Kiely et al., 2013; Mitchell et al., 2009). However, in the Epidemiology of Hearing Loss Study, highly elevated glycosylated hemoglobin levels were associated with a 2-fold increased risk of developing hearing loss during the 15-year follow-up (Cruickshanks et al., 2015b). As with many other risk factors, it is unknown whether the diabetes itself was the cause or only a correlation.
Atherosclerosis Research in animal models, small clinical studies, and early ecological studies have suggested that cardiovascular disease risk factors and processes may be involved in the pathophysiology of hearing loss with aging (Cruickshanks et al., 2010b). One prospective study reported that the intima-media thickness of the carotid artery—a well-known measure of generalized atherosclerosis—was positively associated with the 5-year incidence of hearing loss (Fischer et al., 2015). The risk of developing hearing loss increased by 28 percent for every 0.2 mm increase in the intima-media thickness, an effect similar to what is seen with 5 years of aging. Plaque, a more advanced stage of atherosclerosis, also was associated with an increased risk of incident hearing loss.
Lipoprotein profiles A longitudinal study of 837 people followed for an average of 3.2 years found no association between hearing and the ratios of triglyceride levels or total cholesterol to high-density lipoprotein (HDL) cholesterol (Simpson et al., 2013). Non-HDL cholesterol was not associated with the incidence of hearing loss in either the Epidemiology of Hearing Loss Study or the Beaver Dam Offspring Study (Cruickshanks et al., 2015b; Fischer et al., 2015).
Chronic inflammation Higher levels of markers of inflammation have been associated with many age-related disorders (Chung et al., 2009; Danesh et al., 2008; Ferrucci et al., 2005; Jenny et al., 2012; Kizer et al., 2011). High concentrations of high sensitive c-reactive protein (hsCRP; a marker for inflammation) were found to be associated with a 2-fold increased risk of hearing loss over a 10-year period among people under the age of 60 years (Nash et al., 2014). The risk also increased with the number of such inflammatory markers that were elevated (hsCRP, interleukin-6, and tumor necrosis factor-α). However, no association was found among people age 60 years or older at baseline. A cross-sectional population-based cohort study has demonstrated associations between certain genetic polymorphisms for tumor necrosis factor-α and tumor necrosis factor receptors and hearing thresholds but no associations between other inflammatory-related polymorphisms and hearing loss (Uchida et al., 2014). Thus, chronic low-grade inflammation appears to play an important role in many degenerative disorders of aging and may be important in aging changes in auditory function, but additional prospective data are needed to evaluate its contribution.
Medications Many medications have potential ototoxic effects; the best known are certain antibiotics and chemotherapy agents (Cruickshanks et al., 2010b). There have been few reports from longitudinal cohort studies with audiometrically assessed hearing of associations between medication
usage and the risk of hearing loss. It is not clear if this “absence of evidence” represents a publication bias or the lack of studies assessing medication effects. In the Epidemiology of Hearing Loss Study, no associations were found between the use of nonsteroidal anti-inflammatory medications or lipid-lowering medications (or statins, specifically) and the 15-year incidence of hearing loss (Cruickshanks et al., 2015b). In the study of the offspring of the Beaver Dam participants, statin use also was not associated with the 5-year incidence of hearing loss (Fischer et al., 2015). However, two large cohort studies using self-reported hearing loss outcomes have reported an increased risk of hearing loss to be associated with the use of aspirin, nonsteroidal anti-inflammatory drugs, and acetaminophen (Curhan et al., 2010, 2012). Although it is difficult to study the effects of medications while appropriately accounting for the reasons people use them, for prescription bias, and for polypharmacy, studies are needed to understand the impact of medication usage on changes in auditory function.
IMPACT OF HEARING LOSS
The impact of hearing loss on an individual is highly dependent on the severity of the loss and on the individual’s lifestyle, communication needs, and specific environment. Two people with the same degree of hearing loss as measured by audiometry may report very different hearing difficulties. For example, the hearing “demands” may be quite different for a person who lives alone, is retired, and has a group of friends who socialize in only quiet settings than for a person who is working in a noisy office with cubicles, lives with several people, and frequently dines in noisy restaurants with a large group of friends. Additionally, since humans vary in their reactions to challenges and their abilities to find ways to adjust to changes in health, an individual’s personality, coping style, resiliency, and duration of hearing loss all may influence how that person perceives his or her hearing abilities. In short, there is tremendous heterogeneity in the challenges in everyday life that are attributed to hearing loss because of the complex interactions of individuals and their environments. This highlights the need for a personalized approach to hearing health care.
From a population perspective, the burden of hearing loss may be hard to detect and quantify even in well-designed prospective studies. Studies that have attempted to measure the impact of hearing loss on communication and quality of life have often used questionnaires that measure the overall health-related quality of life, such as the Medical Outcomes Study-Short Form-36 (Ware and Sherbourne, 1992), which was designed for general population surveys. Other studies have relied on instruments that emphasize difficulties with hearing and communication such as the screening versions of the Hearing Handicap Inventory for Adults or the Elderly
(Newman et al., 1990, 1991; Ventry and Weinstein, 1982; Weinstein and Ventry, 1983). Which outcome methodology is an appropriate metric for measuring impact is open to discussion, and efforts to identify improved “real-world” measures are needed (see Chapters 3 and 6).
Although the committee understands that it is not possible to have perfectly randomized controlled trials to examine the impact of hearing loss, prospective studies (preferably population-based) could be designed and well controlled to examine the associations between newly detected hearing loss and subsequent effects on quality of life and function. Such studies would represent the highest level of evidence possible. Existing studies that use prevalent hearing loss often fail to control for the baseline differences accrued prior to the hearing loss or during the hearing loss. Some studies include “outcome” data collected prior to the measurement of hearing, which obscures the prospective trajectories. The following section briefly discusses some of the limited data available from large studies to highlight the gaps in what is known about the effect of hearing loss on the individual’s communication abilities; quality of life; social, occupational, and physical functioning; and health.
Quality of Life and Communication
In the population-based Epidemiology of Hearing Loss Study, participants with hearing loss at the baseline visit had lower quality of life than those with normal hearing, as measured by the 36 item Short Form Health Survey (Dalton et al., 2003). Greater severity of hearing loss also was associated with more communication difficulties, as measured by the Hearing Handicap Inventory for the Elderly, and more limitations in activities of daily living and instrumental activities of daily living (Dalton et al., 2003). Health-related quality of life also was lower in a study of a random sample of people aged 65 and older who had AARP Medicare supplement plans (Hawkins et al., 2012). However, these cross-sectional studies are inadequate for determining the impact of hearing loss as they include both newly detected and longstanding hearing loss and could not adequately control for differences in quality of life that may have preceded the onset of hearing loss.
A longitudinal analysis of data from the Blue Mountains Hearing Study found no difference in the rate of decline in quality of life over a 10-year period between participants with hearing loss and those with normal hearing at baseline, nor was baseline hearing ability associated with the rate of decline in quality of life (Gopinath et al., 2012). Participants who developed a hearing loss during the 10-year follow-up had greater declines in the physical composite score of the Short Form Health Survey than people who retained normal hearing, but there were no differences in the mental composite score (Gopinath et al., 2012).
Cognitive and Mental Health and Depression
A large longitudinal study in Australia found no association between sensory impairments (hearing or vision) and the levels or rates of change in depression during 16 years of follow-up, in multivariable models adjusting for age, sex, and comorbidities (Kiely et al., 2013). The English Longitudinal Study of Aging found no association between self-rated hearing and the onset or persistence of depression (Chou, 2008).
Because hearing loss may burden those people who attempt to communicate with someone who has hearing loss, some studies have measured the impact on the mental health of the spouses of individuals with hearing loss. In the Alameda County Study, baseline self-reported hearing difficulties with communication were associated with the partner’s poorer mental health and well-being 5 years later (Wallhagen et al., 2004). The study controlled for age, gender, financial problems, number of chronic conditions, and the hearing loss of the partner. In contrast, the cross-sectional analyses in the large Nord-Trøndelag Health Study found no association between hearing loss measured by audiometry and spousal mental health in 13,678 couples (Ask et al., 2010). It is not clear if the difference in results was due to cultural differences between the United States and Norway, the longitudinal versus cross-sectional designs, or the differences in impact between measured hearing loss and complaints of hearing problems. It is possible that the burden to the spouse is limited to families where the person who has hearing loss is struggling with communication or is dissatisfied with his or her hearing function.
A link between hearing and cognitive function and dementia has long been recognized, as signals transmitted by the ear are processed and recognized by the brain as sounds and words (Humes et al., 2012). Early studies and reviews have reported an association between hearing loss and dementias (Albers et al., 2015; Uhlmann et al., 1989). The association may be bidirectional, as the Australian Dynamic Analyses to Optimise Ageing project found that cognitive impairment was an independent predictor of the rate of decline in auditory function (Kiely et al., 2012). The Maastricht Aging Study analyzed the relationship that hearing and change in hearing, along with vision and change in vision, had with changes in cognitive function as measured with a battery of tests (Valentijn et al., 2005). In this study, declines in hearing were associated with 6-year declines in the Visual Verbal Learning Test (total score and recall), but not with any of the six other tests included in the battery. No effect of hearing aids was seen, but only seven people were fitted, so the power to detect an association was low. In one longitudinal study of people with audiometrically measured hearing loss, there was no difference between hearing aid users and nonusers in cognitive function or mental health after 11 years of follow-up (Dawes et al., 2015).
Several prospective studies of hearing and incident dementia or Alzheimer’s disease have been conducted. In a sample of the Baltimore Longitudinal Study of Aging, which excluded people with cognitive impairment at baseline, the risk of dementia was found to be 24 percent higher for every 10 dB of hearing loss after adjusting for age, sex, race, education, diabetes, smoking, and hypertension, and baseline scores on one test of cognitive function (Lin et al., 2011a). Hearing aid use was not found to have an effect on the risk of dementia in this study (Lin et al., 2011a). A smaller association was seen in the Health ABC cohort: The risk of having cognitive impairment increased 7 percent for every 10 dB of hearing loss at baseline (Lin et al., 2013). Baseline hearing loss was also associated with a slightly greater annualized decline in scores on the Modified Mini-Mental State Examination and Digit Symbol Substitution test, although the analyses did not control for baseline scores on those tests, which were worse among those with hearing loss than among those without hearing loss. Hearing aid use was not associated with slower rates of decline or a lower incidence of cognitive impairment in that study (Lin et al., 2013).
A subset of the participants in the Baltimore Longitudinal Study of Aging was followed with magnetic resonance imaging. With a mean follow-up time of 6 years, the rates of whole brain atrophy and atrophy in several regions of the right temporal lobe were greater among people with baseline hearing loss than among normal-hearing participants (Lin et al., 2014). Most participants had only a mild hearing loss, and baseline volumes were similar between those with and without hearing loss. The limited studies published to date provide intriguing evidence suggesting that sensorineural hearing loss and cognitive function changes may co-occur in aging. Mechanisms for these associations are not known although shared pathways such as vascular and inflammatory damage or the effects of hearing loss on social isolation and cognitive load have been suggested (Lin et al., 2011a, 2013, 2014; Panza et al., 2015). Future studies are needed to determine the mechanisms of these possible associations.
Studies using self-reported hearing loss are problematic because of the complex relationship between the severity of loss measured by audiometry and the daily impact on function. It is difficult to separate the effects of the actual hearing acuity from other factors that influence self-perceived problems. In one study that controlled for hearing impairment severity, older adults reported less handicap than younger adults, which may reflect differences in demands on hearing, generational differences in coping, or adaptation to hearing loss over time (Wiley et al., 2000). Future studies based on self-report should include measures of the psychosocial factors
that may influence reporting and audiometric testing in order to understand the influences on perceived handicap. Improved measures of hearing are needed—and, in particular, measures that better assess the real-world hearing environment.
The evidence to date on the relationship between hearing loss and social isolation is based on small cross-sectional studies. While it is highly likely that people with severe age-related hearing loss may feel isolated and that some people may respond to changes in hearing by altering their lifestyles, prospective studies are needed to provide stronger supporting evidence. Population-based longitudinal studies of hearing and social isolation are needed to measure the amount of time that adults spend engaging with others or spend in difficult listening conditions in order to determine the effects of different severities of hearing loss and value of treatment.
Other approaches to measuring the importance of hearing loss have evaluated the impact on work. One large study reported finding no association, in a multivariable-adjusted model, between difficulty hearing in noise and the use of sick leave (Nachtegaal et al., 2012). In the Epidemiology of Hearing Loss Study, there was no association between hearing loss at baseline and the 15-year risk of retiring after adjusting for age, sex, self-reported health, and chronic diseases (Fischer et al., 2014).
Cross-sectional studies have examined the association of hearing loss with falls, declines in physical functioning, and hospitalization, but population-based longitudinal studies are lacking. In cross-sectional data from the NHANES study, hearing loss was associated with an increased risk of self-reported history of falls in the previous 12 months (Lin and Ferrucci, 2012). In a subset of the Health ABC study, hearing loss at the 5-year follow-up (2002–2003) was associated with frailty that developed between the baseline examination (1997–1998) and the 10-year follow-up (Kamil et al., 2016). In a study examining hospitalization of the participants in the Health ABC study, participants with hearing loss at the 5-year midpoint examination were likely to have been hospitalized earlier (time to first hospitalization) than those with normal hearing and to have had a higher annual rate of hospitalization over the course of the study (median follow-up was 12 years) (Genther et al., 2015b).
One longitudinal study evaluated the effect of hearing impairment on independence and the use of support services. In the Blue Mountains Hearing Study, 1,457 participants at the baseline hearing test visit reported no use of community support services. Baseline hearing loss was not associated with the 5-year incidence of using community support services, with receiving help from a nonspouse family member or friend, or with an inability to go out alone. However, people with moderate to severe hearing loss had a 2.7-fold increased risk of needing help from family and friends (Schneider et al., 2010). These results provide some evidence that people with severe
levels of hearing loss may have a greater need for services than people with normal hearing.
Two studies using self-reported hearing loss analyzed the impact of hearing loss on access to general health care. The Wisconsin Longitudinal Study found that the odds of reporting difficulties and delays in accessing health care in the previous year were 1.85 times higher in the group reporting hearing loss than in those not reporting hearing loss (Pandhi et al., 2011). In the Medical Expenditure Panel Survey, people with hearing loss were found to have better access to health care than those with other disabilities (Horner-Johnson et al., 2014). Several studies (Contrera et al., 2015; Fisher et al., 2014; Genther et al., 2015a; Gopinath et al., 2013; Wahl et al., 2013) have reported longitudinal associations between hearing and mortality risk; however, most showed no association after controlling for confounding factors (Contrera et al., 2015; Genther et al., 2015a; Wahl et al., 2013). The study authors did not speculate on the reasons for these disparities.
Impact of Early Life Onset of Hearing Loss
One subset of adults with hearing loss that deserves particular attention is those adults who had congenital or childhood-onset hearing loss. Programs exist to identify infants and young children with hearing loss who need treatment. Although hearing health care and hearing aids may be provided to these children through private insurance or state and federal programs, coverage changes as these children transition to adulthood (see Chapter 5). Because hearing aids are frequently used by children with hearing loss, long-term hearing health care is needed to help them continue to thrive as adults. Vocational rehabilitation programs provide assistance for some but may be inadequate to provide support for all who need it (see Chapter 5).
The National Longitudinal Transition Study-2 evaluated post-secondary school outcomes for young adults with disabilities (Newman et al., 2011). No information was collected specific to hearing health care needs or current treatments, but a broad array of outcomes was measured. Most analyses focused on comparing the group with disabilities to the general population and then comparing within the group with disabilities by the type of disability. As seen in Table 2-4, young adults with disabilities were as likely to enroll in post-secondary schools as the general young adult population but were slightly less likely to have graduated within 8 years. Employment rates and duration were similar, as were the number of hours worked, but the average hourly wage was slightly lower, possibly reflecting a higher proportion of part-time workers (Newman et al., 2011). A high percentage were engaged in work, education, or training during this early adult period.
National Longitudinal Transition Study-2: Post-High School Outcomes of Young Adults with Disabilities Up to 8 Years After High Schoola
|General Population||All Disabilities||Hearing Impairment||Deaf-Blindness|
|Mean (SE)||Mean (SE)||Mean (SE)||Mean (SE)|
|Ever enrolled in any postsecondary school||67.4 (0.60)||60.1 (2.63)||74.7 (4.24)||56.8 (7.09)|
|Graduated any postsecondary school||52.4 (1.02)||40.7 (3.71)||52.9 (6.16)||27.7 (9.14)|
|Employed at time of interview||66.1 (0.60)||60.2 (2.65)||57.2 (4.89)||30.1 (6.69)|
|Average duration of employment (months)||21.8 (0.28)||23.5 (1.42)||22.4 (2.59)||19.1 (3.74)|
|Average hours worked per week||37.1 (0.18)||35.8 (0.88)||31.3 (1.47)||24.7 (2.77)|
|Average hourly wage||$11.40 ($0.17)||$10.40 ($0.32)||$10.50 ($0.58)||$9.20 ($1.64)|
|Paid vacation or sick leave||56.6 (0.72)||54.6 (3.31)||49.6 (6.46)||43.8 (10.67)|
|Health insurance||55.5 (0.79)||47.7 (3.32)||40.4 (6.31)||29.2 (9.78)|
|Retirement benefits||38.7 (0.78)||39.0 (3.30)||41.5 (6.43)||31.5 (9.99)|
|Engagement in education, employment, or training since high school||94||95.4 (2.04)||85.0 (5.11)|
|Lived independently||59.0 (1.63)||44.7 (2.68)||50.5 (5.01)||26.4 (6.56)|
|Lives semi-independently||1.8 (0.18)||1.7 (0.70)||6.0 (2.38)||8.2 (4.09)|
|Have had or fathered a child||28.4 (0.57)||29.4 (2.63)||20.6 (4.48)||7.4 (3.95)|
|Married||19.3 (0.53)||13.4 (1.97)||11.4 (3.50)||3.8 (2.86)|
|Savings account||63.3 (0.92)||59.0 (2.86)||64.7 (5.32)||64.3 (7.22)|
|Checking account||73.9 (0.80)||58.7 (2.85)||73.5 (4.89)||46.9 (7.47)|
|Credit card||61.1 (0.92)||41.4 (2.85)||52.9 (5.59)||29.2 (6.81)|
|Food stamps||15.1 (5.56)||38.8 (13.13)|
|General Population||All Disabilities||Hearing Impairment||Deaf-Blindness|
|Mean (SE)||Mean (SE)||Mean (SE)||Mean (SE)|
|Friends outside of school or work weekly||78||76.3 (4.79)||62.3 (7.31)|
|Communicating by computer daily||32.0 (2.69)||51.4 (5.50)||41.2 (7.37)|
|Community participation||51.7 (2.73)||59.3 (4.86)||66.9 (6.78)|
|Driver’s license/learner’s permit||77.7 (2.40)||83.5 (4.07)||26.9 (6.64)|
|Registered to vote||71.0 (2.64)||71.0 (5.04)||56.9 (7.42)|
NOTE: SE = standard error.
aN = 4,810 in Wave 5 that were out of high school when interviewed in 2009; 13- to 16-year-old students were selected in Wave 1, and their average age was 14.4 years in 2000; 40.2 percent of Wave 5 participants were 24 years or older; 65.6 (2.57) percent white, 20.2 (2.17) percent African American, and 14.2 (1.89) percent identified as Hispanic in Wave 5 interviews.
As young adults, they were becoming independent, forming relationships, moving out on their own, driving, and voting at high rates. The set of young adults with hearing loss appeared to be quite similar to the entire study cohort and to the general population on many measures. The majority of both groups saw friends weekly, engaged in community activities, and were registered to vote. In summary, this study showed that children with hearing loss transition to adulthood similarly to young adults without hearing loss in many ways. However, there are very limited data about their hearing health care needs or how its affordability may limit their access and opportunities.
Economic Burden of Hearing Loss
There are no population-based longitudinal data that measure the economic impact of hearing loss. Modeling the economic cost to society of hearing loss has been approached in several ways with varying assumptions. Mohr and colleagues (2000) focused on severe to profound hearing loss and estimated the costs over a lifetime to an individual to be $297,000 (averaged across age at onset), with most of the losses (67 percent) due to reduced work productivity. The study estimated that persons who experience severe to profound hearing loss before retirement are expected
to earn only 50 to 70 percent of what their peers earn who do not have hearing loss. Ruben (2000) used several sources of labor and disability data to look at the economic effects of communications disorders, with some data focused on hearing loss, and found negative impacts of hearing loss on individual income and significant underemployment of individuals with hearing loss. Stucky and colleagues (2010) used a simulation model based on national estimates of the prevalence of hearing loss in individuals age 65 years and older across the range of hearing loss, as well as several sources of economic data, and estimated that the total costs of first-year treatment of hearing loss in 2002 were approximately $1,292 per person, or $8.2 billion nationally, and projected that by 2030 these costs would increase to approximately $51.4 billion nationally. They also estimated the 2002 lost productivity costs attributable to hearing loss in this age group to be approximately $1.4 billion nationally. Simpson and colleagues (2016) examined health care cost data from privately insured adults age 55 to 64 years and found higher health care costs for a number of chronic health conditions for individuals with a diagnostic code for hearing loss as compared with a matched group without that diagnostic code. Emmett and Francis (2015) examined data from the 1999–2002 cycles of NHANES that included audiometric evaluation and a questionnaire on income. Their study found hearing loss to be associated with a 1.58 times higher odds of low income and 1.98 times higher odds of being unemployed or underemployed in adults age 20 to 69 years. The authors noted that these are cross-sectional data that cannot be used to establish causation and pointed to the need for longitudinal studies.
PREVENTION OF HEARING LOSS
Only one small, randomized controlled trial has been conducted to evaluate interventions (other than hearing technologies) for age-related hearing loss (Durga et al., 2007). This trial of folic acid supplementation in the Netherlands demonstrated that in a group of 50- to 70-year-olds, those participants who received 800 µg/day of folic acid experienced smaller declines in hearing at low frequencies (pure tone average 0.5–2 kHz, both ears) during a 3-year follow-up period than did participants who received a placebo (1.0 dB versus 1.7 dB HL, respectively) (Durga et al., 2007). Although this study is not generalizable to the United States where foods are fortified with folate and thus additional supplementation may provide little additional benefit, it suggests that certain nutritional interventions may delay or slow the deterioration of hearing with aging.
Hearing loss prevention efforts targeting all ages largely focus on reducing exposure to intense noise or to sustained high levels of noise by reducing noise volume or increasing the distance from the noise source; by using ear
muffs, ear plugs, or other hearing protective devices; and by using other noise-reducing strategies (NHS, 2015; NIDCD, 2008). Additionally, the avoidance of ototoxic medications, some specific chemical exposures, and other environmental exposures of concern can be considered. Whether healthy lifestyles have any benefits in preserving auditory function remains to be seen.
The risk factors and exposures reviewed above preceded the development of hearing loss, but these factors may not cause hearing loss. Evidence that there are modifiable risk factors for hearing loss is limited by the paucity of prospective, population-based data. There is suggestive evidence that socioeconomic status and obesity are associated with a risk of hearing loss. The reported prospective associations summarized above, along with the pronounced decline in hearing loss across generations, suggest there may be ways to reduce the risk or slow the progression of hearing loss with aging. Additional prospective studies are needed to replicate these findings and strengthen the evidence. Randomized controlled trials of interventions to determine the impact of reductions in obesity or waist circumference on hearing may be warranted. Including measures of hearing in trials aimed at reducing hyperglycemia, atherosclerosis, and chronic inflammation for other health reasons may help to elucidate the roles of these conditions in declining hearing acuity among adults.
For age-related hearing loss, there is insufficient evidence to support interventions for primary prevention. However, ongoing research is seeking to identify drugs that act on oxidative stress pathways, inflammation, and hormonal regulation that may have beneficial effects on hearing. Although some surgical and medical treatments are available for some forms of middle-ear disease and sudden-onset hearing loss, there are no medical or surgical treatments to cure age-related hearing loss. At this time, tertiary prevention methods for helping individuals manage their hearing loss and reduce the impact of hearing loss on their quality of life are available (see Chapters 3, 4, and 6).
NEXT STEPS AND RECOMMENDATION
The paucity of data in many areas of hearing health care will be highlighted throughout this report. Given the number of people with hearing loss and the opportunities to improve their function and quality of life, more can be done to strengthen the evidence base. Of the numerous factors that have contributed to hearing health care’s lack of a strong research base, the committee describes just a few:
- Lack of health insurance coverage for hearing health care—Evidence of improved patient outcomes is a general requisite for
health insurers, policy makers, and others making decisions about payment for health care interventions. However, because few health insurance plans or programs provide reimbursement for hearing health care (see Chapter 5), there has not been a demand for this research.
- Nature of the devices and interventions—Hearing aids are fairly low-risk medical devices, and the Food and Drug Administration’s regulatory processes for approval of hearing aids do not require clinical trial data (unless significant changes are sought to previously approved models). Therefore, randomized controlled clinical trials evaluating the efficacy of hearing aids to improve health outcomes have been limited (see Chapter 4).
- Research training changes and public health emphasis—In general, hearing loss has not been viewed as a public health concern, and audiologists and others are often not trained in public health research methodologies. Additionally, health services researchers, health economists, and epidemiologists receive little training about sensory disorders. Strengthening the research training programs and encouraging multidisciplinary teams to address the many research needs will improve the quality of the evidence in hearing health care.
The research needed to advance the effectiveness of hearing health care services and technologies, particularly comparative effectiveness studies, is described in Chapters 3 and 4. Chapter 5 discusses cost effectiveness research and details the urgency for demonstration projects and other studies to be conducted to fill the gaps in research on interventions, outcomes, and impacts. In addition, research efforts also need to focus further on improving public awareness, reducing stigma, and engaging community organizations and businesses in ensuring that hearing- and communication-friendly environments are available (see Chapter 6).
Well-designed longitudinal population-based studies that adequately control for confounders are needed to definitively determine the impact of hearing loss on adult individuals, families, and society. Additionally, the gaps in population-based surveillance efforts pertinent to hearing loss include insufficient knowledge about variations in the incidence of hearing loss among and across racial and ethnic populations and across geographic areas and insufficient knowledge about the impact of hearing loss on social function, employment, quality of life, independence, and the need for social services. This absence of evidence is striking given that the Global Burden of Disease project has ranked hearing loss as the fifth leading cause of years lived with disability—higher than other chronic diseases of aging such as diabetes, dementia, and chronic obstructive pulmonary disease
(Global Burden of Disease Study 2013 Collaborators, 2015). Learning more about the economic burden of hearing loss should be a priority.
Strengthening research in hearing health care will need to involve a more robust set of metrics for assessing and defining hearing loss and communication abilities, with a focus on measures that are applicable to communicating in the complex environments of daily life. This goal has also been identified in the NIDCD Strategic Plan (NIDCD, 2015). As noted above, further collaborative and interdisciplinary efforts in hearing loss research are needed. Additionally, training in research methodologies needs to be strengthened for audiologists and other hearing health care professionals. Accreditation organizations involved with monitoring education programs could incorporate requirements for research training into standards for academic programs.
Data sources and research opportunities also need to be expanded. The current focus of the hearing-related programs at the CDC is on childhood hearing loss and newborn screening (CDC, 2015b). In addition to these vital programs, it is important to expand CDC’s role and research in adult hearing loss to ensure that this serious public health concern benefits from the population-based approaches and public health opportunities that are available through CDC and through state public health departments.
Goal 1: Improve Population-Based Information on Hearing Loss and Hearing Health Care
Recommendation 1: The National Institutes of Health, the Centers for Disease Control and Prevention, the Patient-Centered Outcomes Research Institute, the Department of Defense, the Department of Veterans Affairs, state public health agencies, and other relevant government agencies, as well as nonprofit organizations, hearing health care professional associations, academic institutions, and researchers, should strengthen efforts to collect, analyze, and disseminate prospective population-based data on hearing loss in adults and the effects of hearing loss and its treatment on patient outcomes.
- Support and conduct studies to develop, evaluate, strengthen, and align metrics for hearing loss and communication abilities;
- Support and conduct studies, including longitudinal studies, in diverse populations to better understand
- the risk and natural history of hearing loss,
- risk factors and comorbidities of hearing loss,
- hearing health care needs, and
- the impact of hearing loss and its treatment on health, function, economic productivity, and quality of life; and
- Develop and strengthen research training programs to address hearing loss as a public health concern with attention to cross-disciplinary training on sensory disorders, epidemiological methods, advanced biostatistics, and health services and health economics research methods.
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