Hearing Loss Among Older Adults: Epidemiology, Disparities, and Gaps in Research

Abstract

The percentage of older adults with hearing loss increases dramatically with age, as does hearing loss severity, yet hearing aid use lags substantially behind prevalence due, in part, to affordability and accessibility barriers for hearing care. Recent studies have demonstrated that hearing loss is closely linked to onset of dementia, declines in cognitive, physical, and social function, and poorer healthcare utilization. Recent gold-standard randomized control trials suggest hearing care modifies poor health outcomes in some older adults. Concurrent to research, policy efforts have attempted to narrow the gap in hearing aid ownership. . This article will review the evidence and gaps in research on an issue of critical health and economic importance..

INTRODUCTION

Hearing loss among older adults has traditionally been portrayed as an irksome but benign consequence of aging. However, an explosion in public health literature over the past 15 years suggest hearing loss is associated with important negative health consequences including cognitive decline, dementia, health resource utilization, and physical function/activity. Concurrent literature has underlined the high prevalence of hearing loss– nearly half of adults ≥60 years and nearly all adults ≥90 years have hearing loss – and the relatively low uptake of hearing aids, only 15–30% of adults with hearing loss (104). As such, hearing loss among older adults has emerged as a national priority in the United States and across the globe with policies aiming to improve access to hearing care. This review will summarize the current state of population-based hearing loss research, with a focus on disparities in research and care, and the critical research gaps that must be addressed to advance equity and promote research translation to improve clinical care and public health policy.

WHAT IS HEARING

Fundamentally, hearing can be broken down into two steps: peripheral encoding of sound (e.g., speech, music, environmental sounds) by entering the outer and middle ear (e.g., pinna, ear canal, and ossicles) for funneling to the cochlea (organ of hearing) where sound is transformed into a neural signal for central decoding by the brain in coordination with other inputs (e.g., visual, contextual, nonverbal cues) (97). Impairment can occur at different points along the pathway including blockage of the outer and middle ear (e.g., fluid in the middle ear), degeneration of cellular structure (which does not regenerate) in the inner ear, damage to the 8th nerve for signal transduction, or neural damage to the brain.

Age-related hearing loss, a broad term that describes damage to the cochlea’s cellular structure from multiple causative factors over the life-course (e.g., noise, genetic predisposition, oxidative damage, age) that results in less precise encoding of auditory signals, is the most common form of hearing loss. Damage occurs at different frequencies at different rates (typically, higher frequencies first), resulting in hearing loss not being an overall volume issue (e.g., all sounds are decreased) but more like a poor radio or cellular signal where some sounds are missed but others detected. For speech, this might result in the word ‘sphere’ being mistaken as ‘ear.’ This leads to the common refrain of “I can hear you, but I can’t understand you.”

Environmental factors and cognitive ability impact hearing beyond peripheral encoding. Hearing loss may not be apparent in a quiet setting when individuals are speaking face-to-face as more mild degrees of degradation in the encoding of the incoming sound can often still be well “compensated” for by the decoding that occurs in the brain, particularly with input from other cues (facial expressions and lip movements). In contrast, settings with background noise (e.g., emergency room or busy hospital floors) can become extremely difficult as the competing background noise further degrades the incoming auditory sound for the impaired cochlea which results in a highly distorted signal that cannot be effectively decoded by the brain. Importantly, decoding auditory signals can be even more problematic for older adults with cognitive impairment given that the same neural resources that underlie cognitive function also subserve central decoding of sound.

MEASUREMENT MATTERS

Different Hearing Measures Represent Different Hearing Constructs

Hearing loss is measured using objective tests and self-reported by participants. Different measures capture different dimensions of hearing ability and range from testing the auditory periphery (i.e., hearing in the ear) to the central cortical processing of speech (i.e., hearing in the brain) (Fig. 1).

Figure 1.

Hearing measures as they progress from peripheral (access to sound) to central (processing of sound).

Pure tone air-conduction audiometry is the clinical gold standard to measure the peripheral ability of the cochlea to encode a simple pure tone. Audiometric threshold finding validly and reliably identifies the quietest level at which someone can hear a tone over a range of pitches (14, 57, 97, 104). Recent advances in portable audiometers -testing for ambient noise levels to ensure valid testing, automated testing algorithms and cloud storage- allow rapid and valid testing in the field (<10 minutes) (48). Audiometry is typically considered the most objective measure that can be collected in large population studies, as other measures of peripheral function identify hearing loss presence but not severity (e.g., otoacoustic emissions). Audiometric data may be validly collected even in mild dementia (81). Studies that use audiometric screening procedures (e.g., ability to hear a tone played once at a given volume for several pitches) should be distinguished from studies using threshold finding. The issue is not in the use of screening methods, but in a possible incorrect interpretation that they identify hearing loss with the same validity as threshold finding.

On the other end of the spectrum, the cortical central auditory processing system integrates the peripheral auditory signal with complex higher-order cognitive processes to decode the peripheral signal and understand speech. Executive functions controlled by the frontal and parietal lobes, including attention and planning, are needed for the separation of sounds in background noise, localization of sound, and combining complex sounds into identified speech (43, 52). Common clinical measures include word recognition and speech-in-noise tests.

Self-report often involves Likert questionnaires (“a little trouble”, “a lot of trouble”, etc.). Many individuals with audiometric hearing loss self-report no hearing difficulty (3, 55), and some who have normal audiometric thresholds self-report trouble hearing (55, 121). In community-dwelling U.S. adults aged ≥70 years, factors associated with misreport of hearing compared with audiometry included age, education, income and smoking status (55). Importantly, misreport can go in either direction. Although older adults are more likely to underestimate their audiometric hearing loss, individuals with higher educational attainment are more likely to overestimate loss with self-report (55). Importantly, factors associated with differential self-report are often associated with disease risk, and so choice of measurement method for hearing loss may result in different estimates of (and even inference relating to) hearing-outcome associations(19). Critically, self-report, as a measure of the individual’s perceived impact of hearing loss within their social and physical environment, captures a different dimension of hearing than objective measures. Both are important, but researchers should not assume that self-report hearing reflects objective measurement and should match the appropriate measurement method to their research question.

The Choice of the Hearing Measure in a Study Impacts Inference

Unfortunately, many studies do not differentiate between hearing constructs, lumping all measures under the label of ‘hearing loss’. This is perhaps due to the traditional siloing of research training and funding. Cognitive aging researchers are generally untrained in how to measure, interpret and analyze hearing data, and likewise, hearing researchers often focus on biology and treatment, without a focus on downstream consequences (66). Public health research often fails to delineate between the two inter-related auditory systems – peripheral and central – needed to process and understand speech. Although the central system relies on the peripheral signal, it also involves higher-order cognitive processes. For this reason, some researchers have suggested that speech understanding measures are essentially cognitive tests of executive function (42). Therefore, although peripheral hearing loss may be a causal risk factor for aging-related outcomes, it may be more appropriate to consider speech understanding as a non-causal risk marker. To avoid incorrect study conclusions, research questions motivated by causal frameworks should use peripheral measures. Questions related to central processing, or those not requiring causal assumptions (e.g., screening) may use speech understanding.

The use of self-reported hearing to approximate audiometrically measured hearing loss is also problematic. Although the overall concordance is ~70%. estimated associations with outcomes can and do differ depending on how hearing is measured (55). In a study of 1,669 adults aged ≥70 years, estimated associations with self-reported outcomes (e.g., self-reported healthy days, functional difficulty) were consistently stronger when hearing was modeled using self-report versus audiometry among the same analytic sample (19). A possible explanation is same-source bias – where exposure and outcome appear spuriously linked because the measurement error for both measures is correlated (33). This is not to say that self-reported measures should be avoided or are less valid than objective measures. On the contrary, an individual’s internal experience cannot be objectively measured, and so must self-reported. The error in interpretation occurs when a measure of an individual’s perception of their hearing is used to approximate what is physiologically occurring in the ear.

PREVALENCE AND RISK FACTORS

Hearing Loss Prevalence

Prevalence is the proportion of individuals in a population at a given time experiencing a specific health state (16). Although tempting to provide a single number to identify prevalence, because estimates are tied to a given population, they will differ across populations with different characteristics. Key population characteristics impacting hearing loss prevalence include person (e.g., age), place (e.g., geographic location), and time (e.g., calendar year). Although some authors prefer the term ‘hearing impairment’ when discussing prevalence, as ‘hearing loss’ could be interpreted as change in hearing from a prior measured level, given the community’s general preference for ‘loss’ over ‘impairment’, we use ‘hearing loss’.

Over 65% of adults aged ≥71 years in the United States have hearing loss (21.5 million individuals) (104), with similar estimates worldwide (129). Prevalence roughly doubles with each increasing decade −27% in 60–69-year-olds, to 55% in 70–79-year-olds, and nearly all individuals ≥85 years (over 90%) (68, 104). Hearing loss severity also increases with age (45, 104). Hearing loss is more prevalent in males than females (1/3 of males vs. 1/5 of females aged ≥40 years) (45). This difference could be due to differences in risk factor profiles by sex (e.g., noise exposure) or possible protective effects of estrogen (65, 82). However, the difference in prevalence of hearing loss by sex narrows with increasing age with no difference by age 85(104). Prevalence is lower in non-Hispanic Black populations compared to other race/ethnicity groups (68). This difference is not understood but hypothesized to be biological – perhaps due to protective effects of melanin in the inner ear or to differential susceptibility to noise-related damage by race (50, 90).

Two methodologic considerations that strongly influence prevalence include hearing loss measurement and definition. Generally, prevalence based on self-report is lower than that for audiometry in older adults. Importantly, misclassification by self-report may be especially impactful for the population attributable fraction (e.g., proportion of dementia risk due to hearing loss in a community), which is strongly influenced by risk factor prevalence (55, 118). The choice of definition is the largest methodological influence on prevalence estimates. A pure tone average (average of audiometric thresholds across frequencies) is typically used as a single summary statistic to define hearing in public health studies, but can be calculated as bilateral (both ears) vs. unilateral (one ear), better-ear vs. worse-ear, with different frequencies (e.g. speech vs. high frequency), and with different severity cutpoints. Depending on the definition used, among the same individuals, prevalence ranged from 2.0% to 99.7% in a sample of older U.S. adults (71). Importantly, the World Health Organization recently changed their hearing loss definition, lowering the cutpoint for loss from 25 dB hearing level (dB HL) to 20 dB HL (91). These changes were recommended by an expert panel but lack details on the scientific or clinical rationale, and when applied, increase prevalence estimates among those ≥71 years from 65% to 83% (104).

Risk Factors for Hearing Loss

Risk factors include non-modifiable (e.g., age, race/ethnicity, biological sex, genetic factors) and modifiable (e.g., environmental including noise and heavy metals, ototoxic medication use, and cardiovascular and lifestyle) factors. Hearing loss among older adults represents the life course combination of these factors and how they may interact. Estimated heritability indices for hearing loss range from 0.35–0.55, supporting a genetic contribution (20, 41, 56). However, a limited number of genetic association studies of age-related hearing loss exist which may be due, in part, to a lack of criterion standard audiometric measures in large genetic population studies, and to the various phenotypes and presentations of age-related hearing loss (123). Noise exposure is, perhaps, the largest preventable cause of hearing loss and has a well-documented impact from workplace (e.g., farm, factory, and military settings) and leisure (e.g., gunfire, vehicle noise, and concerts) (64). Despite governmental regulations, an estimated 24% of hearing loss in the United States is attributable to occupational exposure (89, 120). Other well-established and robust causes of hearing loss include the ototoxic effects of various medications and radiation (aminoglycoside antibiotics, quinine derivatives, platinum chemotherapy [carboplatin, cisplatin] and radiation) and various infectious diseases (mumps, rubella, and meningitis) (34, 61). Epidemiologic studies further suggest that exposure to organic solvents and heavy metals, common medications (e.g., analgesic), smoking, and cardiovascular factors may cause hearing loss. However, the results are mixed. Diabetes, for example, is associated with hearing loss. However, statistically significant findings have resulted in negligible and not clinically meaningful differences (60), and some work suggests any association between diabetes and hearing loss loses statistical significance after multivariable adjustment (24, 35, 83). Notably, cardiovascular, ototoxic medication, and environmental solvent or pollutant exposure can increase the detrimental effects of noise on hearing loss. Importantly, pediatric, adolescent, and young adult populations are vulnerable to other genetic and illness-born risk factors not covered here.

HEARING LOSS ASSOCIATIONS WITH AGING-RELATED OUTCOMES

Mechanisms Linking Hearing Loss to Cognitive Aging Outcomes

Mechanisms linking hearing loss to aging outcomes including dementia are unproven, but are broadly include (1) common pathologic cause or biomarker of underlying pathology (e.g., systematic vascular disease impacting both the ear and brain); (2) bias (e.g., incorrect estimates of cognitive performance because the individual cannot hear the cognitive test); or (3) etiologic contributor (e.g., hearing loss increased social isolation leading to cognitive decline).

The first two mechanisms are non-causal but are considered in many public health studies. Hearing loss-cognition associations persist after accounting for common causes (e.g., demographics, lifestyle factors and disease, especially diabetes and hypertension) through study design and statistical techniques (e.g., restriction, stratification, adjustment in regression models). It should be noted, however, that many studies consider hearing loss in isolation, although it often occurs alongside other sensory impairments in older adults, and research interest in the independent and combined effects of multiple sensory impairments is growing. Additionally, whether Alzheimer’s disease pathology contributes to observed sensory declines through a common pathologic cause is debated, and there is a need for mechanistic studies to investigate this research gap. However, if this is the case, it seems probable that sensory declines would be due to neurodegeneration and neuroinflammation, as opposed to Alzheimer’s-specific pathology, such as β-amyloid given that audiometry relies on cochlear transduction and neuronal afferents to brainstem nuclei without significant higher auditory cortical processing (30, 36, 116). However, epidemiologic studies are mixed, and more work is needed (30, 44, 93, 94, 111, 131, 137).

Measurement bias is also a concern, given that cognitive tests are administered visually and/or aurally. If a person cannot hear the test, results would reflect their hearing, not cognition (59). However, well-designed protocols maximize good communication strategies (e.g., quiet room, face-to-face, well-trained psychometrists), studies excluding auditory cognitive tests show hearing loss-cognition associations (29, 74), and studies designed to investigate the role of measurement bias show that cognition can be validly measured in individuals with hearing loss (87).

Causal pathways hypothesized to link hearing to cognitive health include increased cognitive load (i.e., ‘information degradation’ hypothesis), direct effects on brain structure and function (i.e., ‘sensory deprivation’ hypothesis) and increased social isolation and loneliness (128, 136). Cognitive load is the higher cognitive effort needed to process degraded peripheral auditory signals(99, 122). By imposing a constant load on cortical resources that could have otherwise buffered against pathological dementia contributors (e.g., amyloid, cerebrovascular disease), hearing loss may act as an additional ‘hit’ on the brain that reduces cognitive reserve (66), or the ability to maintain cognitive function in the presence of brain pathology (119). However, evidence primarily comes from small experimental studies, perhaps because of the difficulty of measuring cognitive load in populations(62).

Hearing loss changes the brain. Individuals with hearing loss recruit executive networks associated with problem-solving with evidence of cross-modal plasticity between the somatosensory and auditory systems for compensatory processing of degraded auditory signals (13, 95). It is associated with brain atrophy, especially in the temporal lobe (location of the auditory cortex) and worse white matter microstructural integrity in tracts involved in auditory processing (e.g., uncinate fasciculus) (4, 23, 117). However, evidence is primarily cross-sectional. Functional magnetic resonance imaging studies are limited, and how hearing loss impacts brain activity remains unclear (51). Connectivity between the somatosensory, auditory, and visual networks may increase to compensate for hearing loss, whereas cognitive networks such as the salience network, which is responsible for detecting and processing stimuli, show decreased connectivity.

Hearing loss can also impair an individual’s ability to engage in daily communication and participate in social activities. Difficulties in social situations can lead to frustration, mental distress, and social withdrawal. Increased cognitive load can also deplete cognitive resources needed for social activities (7), particularly among those experiencing cognitive impairment. Hearing loss is associated with increased social isolation, an objective measure of social connectedness, and loneliness, the perceived lack of social connection (115). Both have profound effects on the health of older adults (47, 96), including increasing dementia risk (72).

Hearing Loss and Dementia and Cognitive Decline

Hearing loss is an established risk factor for dementia and cognitive decline (72, 74). The Lancet Commission on Dementia Prevention, Intervention and Care has conducted two meta-analyses of the association of hearing with dementia (72, 73). These reports are cited more often than other reviews due to their strong design and requirement for rigorous methodology of the included studies (e.g., prospective follow-up, adjustment for confounders, etc.). In the most recent report, hearing loss increased estimated dementia risk by 32%, contributing to 7% of global cases (72). Six individual observational studies were included (five positive (11, 26, 67, 92, 98), one null (77)). However, there are limitations, including varying measures of hearing loss (ranging from audiometry (11, 26, 67, 77, 92, 98) to clinical screening that may miss cases (92)), inclusion of adults outside the age range that would put them at risk for late-onset dementia (as young as 19 years) (92), use of the same cohort data (3 of the 6 studies) (11, 26, 98), use of studies not designed to test hearing-dementia associations (multisensory impairment (11) and combined associations of hearing loss and depression (98)), and averaging associations across all levels of hearing loss (72), including mild loss that not be severe enough to warrant treatment or impact cognitive decline. The prior Lancet meta-analysis included only three studies but addressed some of these limitations and estimated a 55% increased risk of dementia (26, 37, 67). Results of other meta-analyses agree, suggesting the true magnitude of the hearing loss-dementia association may be 30–50% (53, 74, 135).

While the current observational evidence supports a hearing loss-dementia link, in many ways this field remains nascent. There is a lack of racial and geographic diversity of study populations (72, 73), which is concerning given the growing number of adults with dementia in low and middle-income countries (75). More high-quality studies are needed in diverse populations with longer follow-up periods, consistent and comprehensive hearing assessment, and complete characterization of dementia diagnoses (75).

Hearing Loss and Physical and Social Health

Clinic-based experimental studies suggest a connection between hearing loss and physical function, and observational epidemiological studies show associations with gait speed (63, 114, 125) and poorer lower mobility function (17, 32, 78, 79, 134). These associations could be explained through a common underlying pathology, including concomitant vestibular dysfunction (2, 138), although studies adjusting for vestibular function show an association (78). Hearing loss could cause physical function decline through mechanisms including accelerated cognitive decline, increased cognitive load, or reduced auditory awareness of the environment (12, 128). Few studies have investigated if hearing aids mitigate the association between hearing loss and physical function decline, although clinic-based studies suggest that they improve postural stability and static balance (76, 86, 109, 126), and that the impact of treatment on balance may be stronger among individuals with cognitive impairment (15).

Social engagement has served as an external validity measure when developing hearing-related questionnaires due to the presumed impact of communication on social outcomes (124). However, population-based studies are relatively limited, perhaps due to the assumed relationship. A large systematic review found that hearing loss was consistently associated with loneliness and social isolation, particularly when hearing was measured by self-report, but heterogeneity existed with objective pure-tone audiometric data (115). This may represent a bias (e.g., those who rate themselves as having more hearing loss subjectively may also be more likely to report poorer social outcomes). The review also identified interactions by gender such that hearing loss seems to effect men more than women and identified an inconsistency in the measurement of social outcomes such that all identified studies used a different metric, including unvalidated self-report, single-item questions (115).

Hearing Loss, Labor Force Participation, and Healthcare Utilization

Economic outcome data related to hearing loss has largely been limited to younger populations (e.g., earning/income, workforce participation, educational costs) and to the profound hearing loss and culturally Deaf populations (10, 25). Older adults with hearing loss may also be at risk for poorer economic outcomes as hearing loss could impact communication related to employment and poorer economic outcomes could be mediated by hearing loss’ impact on other health outcomes (e.g., social, cognitive, physical). Recent work in nationally representative datasets report cross-sectional associations between underemployment by hours worked (38) as well as survival analyses suggesting that older adults with hearing loss retire earlier than their peers with an interaction such that those of lower socioeconomic status where particularly vulnerable to early retirement (39).

The association between hearing loss and healthcare utilization has received a lot of attention in recent years. Researchers have proposed that the impact of hearing loss on patient-provider communication, barriers to accessing healthcare (e.g., telephone), as well as health factors like social isolation could contribute to poorer healthcare utilization outcomes. In a large, propensity-matched cohort study, hearing loss was associated with $22000 more in healthcare expenditures, 47% higher rate of hospitalization, 44% higher risk of a 30-day readmission, and 2 days longer, on average, per hospital stay over a 10-year period (100). Similarly, self-report hearing difficulty has been associated with lower odds of satisfaction with healthcare quality (102), having a usual source of care (101), and following through on needed medical care for reasons other than finances (101). A limitation to this work has been a reliance on self-report data and claims data to identify hearing loss which may underestimate the exposure.

INTERVENTION EFFECTS

Amplification, including hearing aids, is a primary line of treatment for hearing loss. However, , it should be noted that hearing aids are rehabilitation, not a cure. Although they provide some benefit to the wearer, they do not restore hearing to normal levels and require time and effort to learn to use. Misunderstanding of how hearing aids work in public health research has perpetuated a lack of understanding for the need for audiological services as part of holistic hearing care and incorrect study designs that compare intervention effects on cognitive function among hearing aid users to those with normal hearing (31, 108).

Randomized controlled trials are the gold standard study design for establishing causal relationships in epidemiologic research (16). This is because, compared to observational studies, randomization protects against bias and confounding, increasing comparability of treatment groups with respect to factors that influence outcome risk. In an ideal scenario, any observed difference in the outcome comparing treatment to control may therefore be ascribed solely to treatment (16, 27).

Observational studies generally suggest that hearing aid use protects cognitive function (133), particularly executive function (110, 132), although not all studies show benefit. However, individuals who have hearing loss and use hearing aids are typically different from those who do not with respect to educational attainment, average income, and health care access and utilization (104). Given that these factors protect against dementia, definitive answers about the effect of hearing aid use to delay dementia and cognitive decline will likely need to come from randomized trials.

The Aging and Cognitive Health Evaluation in Elders (ACHIEVE) study, is the first and largest multicenter randomized controlled trial designed to test the efficacy of a best-practices hearing intervention vs. health education control on 3-year cognitive decline in older adults aged 70–84 years with untreated hearing loss (Clinicaltrials.gov Identifier: NCT03243422) (28, 69, 106). ACHIEVE, nested within an ongoing prospective cohort study, the Atherosclerosis Risk in Communities Study (ARIC) (130), included 238 (24%) ARIC participants and 738 volunteers newly recruited from the surrounding communities. Participants had a mean age of 76.9±4.0 years, 54% were female and 88% self-reported White race. Overall, the study found no effect of hearing intervention to delay 3-year cognitive decline.

However, an important secondary finding is that, in a pre-specified sensitivity analysis stratified by recruitment cohort (ARIC vs. newly recruited), hearing treatment vs. control resulted in a 0.191 standard deviation (SD) units (95% confidence interval [CI]: 0.022, 0.360; p=0.027) slower rate of global cognitive decline in ARIC participants, equating to a 48% reduction in 3-year cognitive decline. There was no average treatment effect for newly recruited participants (69). Although covariates were well-balanced between treatment groups in the total cohort (as expected given randomization), compared to the subgroup of participants who did not benefit, participants who benefited were older; more likely to be female, low income, living alone and self-identified Black race; and have less than a high school education and diabetes. Baseline cognitive scores were substantially lower, and rates of change were faster over follow-up (−0.402 SD units in participants who benefited vs. −0.151 SD units in participants not benefiting) (69).

The interpretation of subgroup analysis results is thorny given that primary study findings were null. However, subgroup analyses can help identify groups who may be more likely to benefit or experience adverse treatment effects. Although caution is warranted in their interpretation, it is important not to dismiss such findings out of hand. In ACHIEVE, the subgroup analysis suggests that a non-pharmacologic hearing intervention delays cognitive decline in an important group of older adults– those with more dementia risk factors who are experiencing faster rates of decline. As with results from any single study, additional high-quality confirmatory research studies are needed in other populations. It may be possible that hearing treatment delays cognitive decline for some individuals, but more work is needed, including a careful investigation of who is most likely to benefit and how hearing treatment impacts brain health.

ACHIEVE has also investigated the effect of hearing treatment on other pre-specified secondary outcomes, with no effect on physical activity (80, 113) or quality of life (49) but 3-year reductions in the mean number of falls (46) and fatigue (8). Treatment vs. control also reduced social isolation changes (social network size, diversity and embeddedness), amounting to the retention of 1 additional person in their social network (103). However, ACHIEVE did not power to detect differences in these outcomes, and future studies designed and powered to test intervention effects are needed. Also, ACHIEVE hearing intervention included more than just hearing aids, highlighting the importance of rehabilitation as part of comprehensive hearing care (69).

INTERVENTION UPTAKE

Hearing care, broadly, involves the identification of hearing loss (screening and diagnosis) and treatment options that include surgical (limited to certain types of relatively rarer conductive hearing loss), over-the-counter and prescription hearing aids (most common; all types of hearing loss), and cochlear implants (surgically placed medical device for more severe hearing loss) (57). Further, pharmacologic options may be on the horizon (84). Traditionally, hearing aids and cochlear implants are paired with aural rehabilitation services focused on expectation, device management, and communication strategies(9). At a public health level, most data on hearing care uptake focused on the self-report ownership and use of hearing aids (104).

U.S. nationally representative data from 1999 to 2006 cycles of the National Health and Nutrition Examination Survey, suggests 14.2% of Americans ≥50 years with hearing loss report wearing hearing aids at least 1 day a week. Moreover, hearing aid use increased with age, which corresponds to increased hearing loss severity, such that hearing aid use increased from 4.3% of adults with hearing loss 50–59 years to 22.1% of adults over 80 years with hearing loss (18). More recently, nationally representative data (U.S.; 2021–22) from the National Health and Aging Trends Study, found 29.2% of adults with hearing loss ≥70 years wore a hearing aid in the last month. Further, hearing aid use increased from 14.4% to 45.3% to 67.9% of those with mild, moderate, and ≥severe hearing loss (104). Notably, data on hearing aid ownership versus use produce noticeable differences that suggest a significant proportion of hearing aids are purchased but not used, underlining a strong need for support services (1, 104). Even in nations where hearing aids are covered by government programs and insurance, hearing aid use remains relatively low (112).

Beyond the overall low prevalence of hearing aid use among adults with hearing loss, hearing aid ownership and use are further associated with sociodemographic factors. An analysis of US nationally representative data from 2011 to 2018 reported a 23.3% overall increase in hearing aid use among 70+ year olds (105). However, further analysis of the data revealed disparities such that White men saw a 28.7% increase in hearing aid use but Black women saw only 5.8% growth over the same 8-year period. More alarming, older adults living at less than 100% of the federal poverty level experienced an overall decrease from 12.4% in 2011 to 10.8% in 2018, whereas older adults living at 200% or above the poverty line saw an increase from 16.4% in 2011 to 21.2% in 2018. This work corroborates cross-sectional analyses reporting lower ownership and use disparities among Black (vs White) Americans, lower income, and in rural Americans (54, 88).

POLICY HISTORY AND ADVANCES

In the United States, hearing aid coverage is a statutory exclusion (i.e., changes requires congressional action) from Medicare, the federal health insurance program for older Americans established by the 1965 Social Security Act (85, 107). State mandates for coverage for employment-related insurance is limited to 26 states as of 2022 (5, 40) and Medicaid coverage for low-income Americans is limited to 28 states as of 2017 (6). As such, hearing care remains a largely out-of-pocket expense and out of reach for many at an average cost of $4700 for a set of hearing aids and professional services(85). Notably, surgical options like cochlear implants are covered by Medicare (85, 107).

U.S. legislative proposals for Medicare coverage of hearing aids rarely make it out of committee. However, the Build Back Better Act of 2021 legislative package included a provision for Medicare expansion to cover hearing diagnostic services, support services, and hearing aids (70). While this version of the Act passed the House of Representatives in 2021 it failed to gain enough support in the Senate by a single vote.

The Over-the-Counter (OTC) Hearing Aid Act of 2017 (passed by U.S. Congress within the Food and Drug Administration [FDA] Reauthorization Act of 2017) was a novel approach to increasing access (70, 127). Following evidence of technologic advances such that lower cost and self-fit devices rivaled outcomes from traditional devices and professional delivery models, the legislation mandated that the FDA create a direct-to-consumer category of hearing aids. The aim of the legislation was to improve affordability by encouraging new market competition that was previously difficult in a marketplace dominated by only five hearing aid manufacturers and improve access by offering additional options to traditional hearing aids that could legally only be dispensed by licensed professionals. In Fall 2022, the FDA finalized the OTC Hearing Aid Category with a notable 510k exemption (21, 58), meaning that devices did not require approval from the FDA based on clinical trial evidence and, rather, were registered with the FDA based on meeting a broad set of technologic minimum characteristics. An alternative category called Self-Fit OTC Hearing Aids was not 510k exempt and did require trial evidence that consumers could self-adjust the devices. However, the marketplace has been flooded by thousands of companies registering as OTC hearing aids which could cause consumer confusion. Currently, it is unclear whether the OTC hearing aid ACT has resulted in increased successful adoption despite major consumer tech brands (e.g., Apple, Sony) joining the marketplace (22).

CONCLUSION AND FUTURE DIRECTIONS

Overall, hearing loss is a near ubiquitous experience among older adults that has progressed from being perceived as a common but benign to a risk factor for negative healthy aging outcomes including cognitive decline, physical function, social engagement, and healthcare utilization. Importantly, this recent work has thrust hearing loss among older adults into media and policy-related attention after decades of work focusing mostly on children and young adults. However, the prevalence of hearing care uptake remains underutilized with disparities among vulnerable populations. While a recent landmark randomized control trial suggests positive effects of hearing intervention on healthy aging outcomes, the overall null result limits the impact on policy recommendations.

Gaps and potential bias and confounding factors impacting current work have been woven throughout this manuscript. Despite huge leaps forward, work remains for public health researchers. At a basic level, the current criterion measure of hearing loss, pure-tone audiometry, has changed little in nearly a century despite only representing one part of the hearing pathway (access to sound) and the categorical cutpoints for hearing may require updating to reflect experiences of older adults. Research in this space must diversify, globalize, and become more inclusive and accessible. The majority of the research described is U.S.-centric and the field is largely based in western countries in homogenous White populations. Moreover, functional disabilities, including sensory loss, are regular exclusion factors in observational and clinical trials, resulting in observed inferences and effect estimates missing representation of the population of interest. Only a handful of large, epidemiologic studies have added sensory measures and confirmatory studies on how hearing impacts outcomes are needed. Mechanistic studies are needed, including mediation analyses between hearing loss and described outcomes and studies that include the impact of noise exposure, which could have a direct or indirect (via hearing and cardiovascular changes) on cognitive decline. The impact of multisensory impairment remains understudied despite vision, olfaction, and hearing loss being common comorbidities. Likewise, intervention research has only scratched the surface. Corroborative gold standard trials are needed in targeted populations but also studies on other interventions (e.g., cochlear implants, pharmacologic outcomes, over-the-counter models) and other settings (e.g., hearing care in nursing facilities or hospital settings). Moreover, how hearing loss modifies responsiveness to other interventions (e.g., psychology or other communication-based interventions) are not just warranted but required to ensure equitable access to research and interventions. There is no shortage of work.