Introduction

Age-related hearing loss is highly prevalent among older adults, and historically has been viewed as an inevitable and relatively insignificant consequence of aging. However, recent evidence suggests that this impression may not be the case, with growing epidemiologic and clinical research demonstrating an independent association between hearing loss and a broad range of negative health, social, and economic outcomes. With an aging population, the number of adults in the USA living with hearing loss is expected to rise from 44 million in 2020 to over 73 million by 2060, which underscores the importance of understanding the impact of age-related hearing loss as well as addressing hearing loss from a public health perspective [1]. The purpose of this review is to summarize recent developments in the epidemiology of age-related hearing loss and advances in the delivery of hearing health care.

Epidemiology of Age-related Hearing Loss

According to nationally representative estimates, two-thirds of Americans aged 70 years or older have clinically significant hearing loss (better ear speech pure tone average > 25 dB), representing 23 million individuals [2,3,4], with this figure projected to increase to almost 50 million by 2060 [1]. Age is the greatest risk factor for hearing loss; the prevalence of hearing loss approximately doubles with each decade of life, from affecting 13% of adults aged 50–59 to over 80% of those 80 years and older [2, 3].

In addition to age, sex is a risk factor for age-related hearing loss. Multiple nationally representative studies and large prospective cohort studies document higher prevalence among males, even when controlling for age and occupational noise exposure [4,5,6]. These differences are most apparent at higher frequencies. Skin pigmentation, assessed through Fitzpatrick skin type or self-reported race/ethnicity, is another risk factor for hearing loss, with those with higher Fitzpatrick rating demonstrating higher density of strial melanocytes in the cochlea and lower rates of age-related hearing loss [4, 7]. Melanocyte activity in the cochlea may serve a protective role and the underlying mechanism for this association [7].

Apart from age, sex, and skin pigmentation, cardiovascular risk factors have been postulated to contribute to hearing loss. These include diabetes, hypertension, and smoking, which are proposed to lead to hearing loss through vascular mechanisms. Recent cohort studies have suggested associations between diabetes and hypertension with higher rates of hearing loss later in life [8, 9]. However, results from nationally representative studies have been equivocal, and these associations have not been consistent across cohorts [4].

Impact of Age-related Hearing Loss on the Individual and Society

Over the past decade, hearing loss has increasingly been recognized as an important factor in healthy aging. Age-related hearing loss has been independently associated with negative outcomes across nearly every domain of aging for individuals. In this section, we will review the existing level of evidence concerning age-related hearing loss and its associations with dementia, social isolation, depression, physical functioning, and quality of life as well as the growing literature of the societal costs of age-related hearing loss.

Age-related Hearing Loss and Dementia

As the world population increases in age, age-related conditions are gaining recognition as significant and growing public health challenges. Alzheimer’s disease and related dementias are rapidly increasing in prevalence, affecting 47 million individuals globally in 2015, and expected to grow to 131 million by 2050 [10]. Due to this rising prevalence and devastating impact on affected individuals, their family members, and caregivers, prevention and treatment of dementia has become a public health priority.

Recent epidemiologic and cohort studies demonstrate an association between age-related hearing loss and incident dementia and accelerated cognitive decline, which raise the question of whether age-related hearing loss is a potentially modifiable risk factor for dementia. Since 1981, numerous studies have demonstrated positive associations between hearing status and cognition, though the association was not consistent, likely due to heterogeneity among definitions of both [11,12,13,14]. Since 2005, multiple prospective cohorts, using objective audiometric determination of hearing status, and adjusting for confounders, such as age and vascular risk factors, have independently determined an association between hearing loss and increased risk of cognitive impairment and incident dementia [15,16,17,18,19,20,21,22,23,24,25]. In one longitudinal study, those with hearing loss had a 30–40% higher rate of cognitive decline compared with those with normal hearing over a period of 6 years [17]. The degree of risk was associated with the severity of hearing loss, with those with mild, moderate, and severe hearing loss having a two-, three-, and five-fold increased risk of incident dementia, respectively, over those with normal hearing during 10 years of follow-up [15]. A 2017 commissioned report in The Lancet performed a meta-analysis of risk factors for dementia, concluding that based on the degree of risk and high prevalence, age-related hearing loss was the largest potentially modifiable risk factor for dementia over the life course [16••].

Despite the strong base of evidence of an association between hearing loss and increased cognitive decline, the underlying mechanisms behind this association remain unknown. Several pathways have been proposed, such as increased cognitive load, structural and functional changes in the brain [26, 27], and decreased social engagement, which is known to contribute to impaired cognitive function [26, 28]. Alternatively, the association between hearing loss and dementia may be explained by a shared pathway, such as microvascular disease, social factors, or biological processes related to aging [26].

Though numerous studies have demonstrated an association between hearing loss, accelerated cognitive decline, and incident dementia, there is a paucity of evidence to directly support treatment of hearing loss as a method for preventing dementia or slowing cognitive decline. Results from observational studies have generally supported a protective effect with hearing aid use, but these conclusions are difficult to interpret, since those with hearing aids tend to be of higher socioeconomic status, but those who seek treatment may also be more likely to have more severe hearing loss [24, 29]. To date, only one randomized controlled trial has been performed investigating the effect of hearing aids and broader “downstream” outcomes [30]. This study, performed in the 1980s, followed a group of veterans over 1 year and demonstrated improvements in social and emotional function, communication, and cognition with hearing aid use [31, 32]. However, more trials must be performed which follow a more representative cohort, incorporate current standards of hearing health care (e.g., digital devices, paired with counseling and education), and follow patients for a longer period.

The Aging and Cognitive Health Evaluation in Elders (ACHIEVE) trial (NCT03243422) is a multi-site, randomized controlled study which began in 2018, investigating the effect of hearing loss treatment on cognitive decline and other functional domains [33]. This trial will follow a cohort of community-dwelling, cognitively normal 70–84-year-old adults with mild to moderate hearing loss, randomizing them to either a hearing intervention (bilateral hearing aid fitting and associated education and counseling) or a control arm that consists of a successful aging intervention. The ACHIEVE trial may provide key insights into whether treatment of hearing loss can slow cognitive decline and the potential underlying mechanisms.

Age-related Hearing Loss, Social Isolation, and Depression

In addition to its effects on cognition, age-related hearing loss has been independently associated with social isolation and depression. Several studies have demonstrated an association between hearing loss, anxiety, and loneliness in older adults, in which more severe hearing loss has been associated with higher levels of loneliness [34,35,36]. Those with even mild or moderate hearing loss were found to have severe deficits in social and emotional function [31]. Regarding depression, several prospective cohort and cross-sectional studies have demonstrated an association with hearing loss, though others did not [37,38,39,40,41]. A recently conducted meta-analysis found significantly higher odds of depression among individuals with hearing loss but did not find that hearing aid use was protective [42]. This is inconsistent with several previous studies which suggested hearing aid use may improve social and emotional function, through reduced odds of depressive symptoms and major depressive disorder in a variety of patient cohorts and settings [38, 41, 43,44,45]. Ultimately, it is difficult to interpret these findings due to the observational nature of the studies, as well as the possible large discrepancy between hearing aid ownership and actual usage. The one randomized trial that has been performed reported sustained benefits in social and emotional function, including depressive symptoms for up to 1 year [31, 32].

Age-related Hearing Loss, Physical Functioning, and Quality of Life

Expanding upon the social and emotional repercussions of age-related hearing loss, many studies have documented an association with physical function. Within the Epidemiology of Hearing Loss Study, a longitudinal, population-based study (n = 2688) conducted in Beaver Dam, WI, older adults with moderate to severe hearing loss were significantly more likely to report functional impairments including limitations in activities of daily living (ADLs) and instrumental activities of daily living (IADLs) [46], which may dramatically affect daily functioning and decrease quality of life. For example, within the Beaver Dam study, those with moderate to severe hearing loss reported lower levels of quality of life [46]. The Blue Mountains Hearing Study, another prospective cohort (n = 2956), also found an association between hearing loss, quality of life, and physical function, with those who regularly used hearing aids reported better physical functioning than those who did not [47].

Building on physical functioning, falls are a crucial component which can have significant repercussions on quality of life. Several studies report a significant association with age-related hearing loss, where those with hearing loss had three times the risk of falls [48, 49]. With decreased physical functioning and impairments in ADLs and IADLs, hearing loss is also expected to impact those who are close to individuals with hearing loss, supported by a study demonstrating increased use of community and informal social support among older adults with untreated hearing loss [50].

Societal Effects of Age-related Hearing Loss

Age-related hearing loss affects not only individuals and their families but also health care systems and society. An epidemiologic study using nationally representative data from the National Health and Nutrition Examination Survey (NHANES) found that after adjusting for demographic and cardiovascular factors, individuals with hearing loss were more likely to have a history of hospitalization in the last year [51]. These results were confirmed in a prospective study using data from the Health ABC study (n = 2148), where individuals with hearing loss experienced a higher incidence of and higher annual rate of hospitalizations [52]. In addition, hearing loss has been associated with decreased levels of satisfaction with health care, possibly mediated by increased difficulty with communication [53]. Hearing loss in older adults has also been independently associated with increased risk of mortality [54]. In addition, older individuals with hearing loss have higher total medical expenditures, according to a study utilizing the Medical Expenditure Panel Survey, which includes a nationally representative sample of Medicare beneficiaries [55]. These expenditures were not solely due to increased hospitalizations, and those with hearing loss had increased odds of emergency room and outpatient visits [55]. A systematic review estimated the total excess medical costs related to hearing loss in the USA to be as high as $12.8 billion [56].

In addition to health care–related expenditures, age-related hearing loss results in substantial overall costs to society through lost productivity and other effects. Using data from the Health ABC study, individuals with hearing loss had higher risk of incident disability, independent of depressive symptoms [57]. For individuals with onset of severe to profound hearing loss at 65 years or older, the overall lifetime costs are estimated to amount to $43,000 per person, though this figure does not include the costs associated with mild or moderate hearing loss, which is more prevalent, nor does it account for the increasing number of individuals working beyond 65 years of age [58]. Overall determination of the total cost to society for adult-onset hearing loss is challenging; specifically for lost productivity, where estimates range from $1.8 to $194 billion [56]. From the individual to society, age-related hearing loss has significant implications, which are only more recently beginning to be understood.

Hearing Health care: Current Paradigm, Barriers, and Recent Developments

Hearing Screening, Treatment, and Care Disparities

Current treatment of age-related hearing loss focuses on aural rehabilitation combined with amplification, usually through hearing aids [25]. Most hearing health care focuses on audiometric screening, followed by fitting and use of amplification devices. The US Preventative Services Task Force has not made a formal recommendation regarding hearing screening for adults 50 years or older due to insufficient evidence, though these recommendations are currently being revised [59, 60]. According to nationally representative estimates, about 40% of older Americans report recent hearing screening, with evidence suggesting minority older adults were more likely to report recent hearing screening compared with white older adults, possibly due to occupational noise exposure and associated screening efforts or differences in benefit coverage through insurance providers including Medicare and Medicaid [29].

Prevalence of hearing loss treatment through hearing aids is low, with representative studies estimating hearing aid ownership or adoption at only 15–20% of older adults with hearing loss [4, 61]. Prevalence of hearing aid use, defined as regular use for 5 or more hours a week, was similar at 20% and, despite advancements in technology, has remained at similar levels for decades [29, 62, 63]. Several studies have reported differences in hearing aid use by race/ethnicity and socioeconomic status, with only 10% of African American and Mexican American older adults using hearing aids, compared with 21% of white older adults [29]. Socioeconomic status, as measured by household income or family income-to-poverty ration (FIPR), is also associated with hearing aid use, with those with the lowest income and FIPR having the highest rates of untreated hearing loss [64, 65]. In another study, among Medicare beneficiaries, those who were dually eligible for Medicaid had 41% lower odds of using hearing health care services, and also were more likely to report difficulties with using their hearing aids once they obtained hearing aids [66]. These disparities in hearing health care reflect overall trends in health care access seen in the USA, and highlight the need for new approaches to age-related hearing loss from a public health perspective [67].

Barriers to Hearing Health care

The overall low prevalence of hearing aid use, as well as disparities across older adults by race/ethnicity and socioeconomic status, is likely a reflection of many complex, interrelated factors, all of which may influence an individual’s ability and willingness to seek hearing health care. Of these, barriers to hearing health care may greatly contribute to the low rate of uptake of hearing loss treatment, yet traditionally, research has not approached these barriers through a public health lens.

The current model of hearing health care is complex with multiple entry points, requiring individuals to navigate through several steps with multiple providers and, at times, without much guidance through the process [68, 69]. This often involves multiple visits for the purposes of audiologic assessment, medical evaluation, counseling, and device fitting, which are not covered by Medicare [69, 70]. The current process of obtaining hearing health care is unfeasible for many older adults, as it requires high levels of mobility, transportation, financial resources, executive function, and health literacy [69]. Older adults, particularly those who are the most vulnerable, face systemic barriers to entering and completing the process of obtaining hearing health care [68]. For example, older adults have the lowest rates of health literacy among all demographic groups, yet the mean reading grade level of training materials and hearing aid manuals is at almost a 10th grade level, above the recommended 6th grade reading level, making them unsuitable for many older adults [71, 72]. Older adults with hearing loss often have age-related vision changes as well, making the operation of small buttons and changing batteries difficult for some [73, 74]. These devices may also utilize a series of beeps or chimes to indicate status, such as current setting or low battery, which, while more universal compared with spoken prompts, are often difficult to interpret for older adults [75]. In addition, social stigma and views on hearing health care, both among older adults and their providers, have restricted access to treatment [76, 77]. A better understanding of these barriers is crucial for developing new models of hearing health care delivery to broaden access to hearing health care for older adults.

Developments in Hearing Health care

In the last several years, tremendous developments have been made in the landscape of hearing health care, including hearing aids and cochlear implantation among older adults. Efforts by leading national organizations have led to increased awareness of the need for more affordable and accessible hearing health care, reduction in barriers to care, and legislative changes at the national level. In 2015, the President’s Council of Advisors on Science and Technology (PCAST) submitted a letter report to the president, recommending the creation of a prescription process for hearing aids, similar to glasses and contact lenses, the creation of a new over-the-counter (OTC) category for hearing aids through the Food and Drug Administration (FDA), and removal of prior FDA guidance around the existing category of personal sound amplification products (PSAPs) [78,79,80]. This was followed in 2016 by a report created by the National Academies of Science, Engineering, and Medicine (NASEM) which included 12 recommendations for increasing access to hearing technology, reiterating the recommendations of PCAST [69, 81].

Following the release of these reports, legislative changes quickly followed. In December 2016, the FDA announced that it would no longer enforce the medical evaluation requirement prior to purchase of hearing aids [82]. At the same time, bipartisan legislation was introduced to create a new category of OTC devices by the FDA [83•,84]. The Over-the-Counter Hearing Aid Act of 2017 was passed with bipartisan support, mandating the FDA to create a new, separate regulatory classification for OTC hearing aids [83•, 84]. These efforts aim to reduce barriers to access and are anticipated to spur innovation through a new market of OTC devices, and, ideally, reduce cost, improve quality, and expand options for older adults. These legislative changes are part of a greater trend of increased public awareness of the need for alternative devices and the recognition of hearing loss as a public health priority.

In addition to national changes in policy around hearing devices, innovations must be made in the delivery of hearing health care, of which device fitting, orientation, and aural rehabilitation play a crucial role [69, 85]. Additional models of care must provide options beyond the traditional, clinic-based model which may not be affordable or accessible to many older adults. Recently, community-delivered hearing care has been proposed as a possible solution, including the incorporation of public health approaches, such as task sharing through community health workers in order to expand access to individuals and communities who have not traditionally obtained hearing care [69,86•,87]. Several pilot studies have demonstrated the feasibility and preliminary efficacy of such approaches. Ovendo Bien is a program based along the USA-Mexico border, where a trained group of Spanish-speaking community health workers (or promotores) delivers group aural rehabilitation sessions to older adults with hearing loss and their families [88]. Another program, HEARS, based in Baltimore, MD, includes a 2-h community-delivered training session combined with the fitting of a low-cost OTC amplification device. An initial pilot study demonstrated preliminary efficacy through reductions in communication difficulty and depressive symptoms in a cohort of urban-dwelling, low-income older adults [89]. These programs both are currently undergoing larger, randomized controlled trials, funded by the National Institutes of Health, incorporating community-engaged approaches to target traditionally underserved populations.

Recently, several programs have emphasized the potential benefits of administering simple, low-cost hearing interventions in a clinical setting, beyond audiology and otolaryngology. Delivery of an educational brochure on hearing loss and hearing health care in a primary care clinic was shown to enhance communication and increase rates of hearing care follow-up [90]. Another study, performed in a memory care clinic, demonstrated that a low-cost OTC device, pared with a one-time aural rehabilitation session, provided benefit for both older adults with cognitive impairment and their caregivers [91]. In the inpatient setting, the ENHANCE pilot study used simple interventions, including low-cost devices, and/or bedside signage offering tips for communication, tailored by patient self-reported hearing status, finding that these interventions improved both patient and nurse satisfaction and did not disrupt nurse workflow [92]. These and other models of hearing health care are needed to expand access and address the needs of more older adults with hearing loss.

Cochlear Implantation in Older Adults

Most individuals with age-related hearing loss have a mild to moderate loss. However, almost 2 million older adults in the US have severe to profound hearing loss, for which amplification alone may not be sufficient [2]. Cochlear implantation, traditionally performed in the pediatric setting, has increasingly been offered as an option to older adults, with institutions performing implants for those over 70, 80, and 90 years old [93,94,95]. Of note, the rates of frailty and comorbidity increase with age and are associated with increased risk of adverse outcomes in surgical patients, such as rates of complications, hospital stay length, and morbidity and mortality [96,97,98]. Frailty is associated independently with hearing loss, and impaired preoperative functional status has been shown to be associated with postoperative mortality after otologic and neurotologic surgery, though specific data on cochlear implantation is limited [99,100,101,102]. Therefore, careful preoperative assessment and management of comorbidities is necessary to reduce risks for older adults undergoing surgery [103,104,105]. For patients who cannot tolerate general anesthesia, there is increasing evidence for the safety and efficacy of performing cochlear implantation under local anesthesia with sedation [106, 107].

Though there are potentially increased risks associated with geriatric surgery, cochlear implantation is safe for many older adults, with complication rates not differing significantly from younger patients [95, 108, 109]. Older adults receive substantial benefits from implantation, including improvements in speech understanding [93]. The satisfaction of older adults with their implants is high at over 80%, and long-term use is also high at over 10 years [110]. However, age at implantation should be considered, since increased age is associated with greater risk of discontinuation of device use as well as decreased magnitude of improvement in speech scores [93, 108, 110]. In addition to age, other factors that are negatively associated with long-term gains from cochlear implantation include lower general health, low education level, and residency in an assisted-living facility [111]. Alternately, familiarity with technology and living with others are associated with increased improvements in speech understanding compared with those who are unfamiliar or live alone [112]. These findings highlight the importance of social factors and the need to consider these broader factors when considering cochlear implantation in older adults.

In addition to improvements in speech understanding, cochlear implantation is associated with benefits to quality of life, particularly across hearing and emotional domains, with increases in quality of life proportional to gains in speech understanding [113,114,115,116]. These improvements translate to gains in health utility corresponding to $9530 per quality-adjusted life-year, which is comparable with those seen among younger cochlear implant recipients, despite fewer years of benefit [116,117,118]. These findings indicate that cochlear implantation in older adults is both efficacious and cost-effective.

Conclusion

Age-related hearing loss is highly prevalent among older adults and is quickly increasing in prevalence as the population ages. Other risk factors include male sex, skin pigmentation, and possibly diabetes and hypertension. Though traditionally regarded as an inevitable and insignificant consequence of aging, age-related hearing loss has increasingly been recognized to be strongly associated with negative outcomes across numerous domains important in aging. Among individuals, hearing loss is associated with higher rates of cognitive decline and incident dementia, as well as loneliness, depression, and limitations in activities of daily living. Societal impacts of age-related hearing loss include increased medical expenditures, hospitalizations, and significant costs due to lost productivity and other factors. Though hearing aids may benefit many older adults with hearing loss, overall adoption remains low, possibly due to multiple substantial barriers to hearing health care. Recent advances in legislation and delivery models hold promise for increasing access to treatment, with the ultimate goal of mitigating the effects of hearing loss.