Hearing Loss, Hearing Aid Use, and Risk of Dementia in Older Adults

Manuella Lech Cantuaria; Ellen Raben Pedersen; Frans Boch Waldorff; Lene Wermuth; Kjeld Møller Pedersen; Aslak Harbo Poulsen; Ole Raaschou-Nielsen; Mette Sørensen; Jesper Hvass Schmidt

doi:10.1001/jamaoto.2023.3509

. 2024 Jan 4;150(2):157–164. doi: 10.1001/jamaoto.2023.3509

Hearing Loss, Hearing Aid Use, and Risk of Dementia in Older Adults

Manuella Lech Cantuaria ^1,^2,^✉, Ellen Raben Pedersen ³, Frans Boch Waldorff ^4,⁵, Lene Wermuth ^6,⁷, Kjeld Møller Pedersen ⁸, Aslak Harbo Poulsen ², Ole Raaschou-Nielsen ^2,⁹, Mette Sørensen ^2,¹⁰, Jesper Hvass Schmidt ^1,^11,¹²

¹Research Unit for ORL–Head & Neck Surgery and Audiology, Odense University Hospital & University of Southern Denmark, Odense, Denmark

²Work, Environment and Cancer, Danish Cancer Institute, Copenhagen, Denmark

³The Maersk Mc-Kinney Moller Institute, University of Southern Denmark, Odense, Denmark

⁴Department of Public Health, Research Unit for General Practice and Section of General Practice, University of Copenhagen, Copenhagen, Denmark

⁵Research Unit of General Practice, Department of Public Health, University of Southern Denmark, Odense, Denmark

⁶Department of Neurology, Slagelse Hospital, Slagelse, Denmark

⁷Department of Regional Health Research, University of Southern Denmark, Odense, Denmark

⁸Department of Economics, University of Southern Denmark, Denmark

⁹Department of Environmental Science, Aarhus University, Roskilde, Denmark

¹⁰Department of Natural Science and Environment, Roskilde University, Roskilde, Denmark

¹¹Brain Research–Inter-Disciplinary Guided Excellence, Department of Clinical Research, Faculty of Health Sciences, University of Southern Denmark, Odense, Denmark

¹²Odense Patient data Explorative Network, Odense University Hospital, Odense, Denmark

Accepted for Publication: November 5, 2023.

Published Online: January 4, 2024. doi:10.1001/jamaoto.2023.3509

^✉

Corresponding Author: Manuella Lech Cantuaria, PhD, University of Southern Denmark, Campusvej 55, 5230, Odense 5230, Denmark (mlca@health.sdu.dk).

Author Contributions: Dr Cantuaria had full access to all of the data in the study and takes responsibility for the integrity of the data and the accuracy of the data analysis.

Concept and design: Cantuaria, E. Pedersen, Wermuth, K. Pedersen, Sørensen, Schmidt.

Acquisition, analysis, or interpretation of data: Cantuaria, E. Pedersen, Waldorff, Poulsen, Raaschou-Nielsen, Sørensen, Schmidt.

Drafting of the manuscript: Cantuaria, K. Pedersen.

Critical review of the manuscript for important intellectual content: E. Pedersen, Waldorff, Wermuth, K. Pedersen, Poulsen, Raaschou-Nielsen, Sørensen, Schmidt.

Statistical analysis: Cantuaria, K. Pedersen, Sørensen, Schmidt.

Obtained funding: Cantuaria, E. Pedersen, Sørensen, Schmidt.

Administrative, technical, or material support: Wermuth, Poulsen, Schmidt.

Supervision: Wermuth, Raaschou-Nielsen, Sørensen, Schmidt.

Other - data management: Cantuaria.

Conflict of Interest Disclosures: Dr Cantuaria reported grants from the William Demant Foundation during the conduct of the study. Dr Schmidt reported grants from the William Demant Foundation during the conduct of the study as well as grants from Innovation Foundation Denmark, William Demant Foundation, Interfond, Oticon, GN Hearing, and Widex-Sivantos and nonfinancial support from Interacoustics outside the submitted work. Dr E. Pedersen reported grants from the William Demant Foundation during the conduct of the study and outside the submitted work. No other disclosures were reported.

Funding/Support: This work was funded by the William Demant Foundation (grant 18-0964).

Role of the Funder/Sponsor: The funding organizations had no role in the design and conduct of the study; collection, management, analysis, and interpretation of the data; preparation, review, or approval of the manuscript; and decision to submit the manuscript for publication.

Data Sharing Statement: See Supplement 2.

Additional Contributions: We acknowledge the extensive contribution of Lisbeth Kjems Christensen (AMGROS) and the staff at the Center for Communication and Welfare Technology (especially Jan Hoedt) for giving us access to hearing aid data (ie, Regional Hearing Aid and the Battery database). Neither AMGROS or the Center for Communication and Welfare Technology were compensated for their contributions.

^✉

Corresponding author.

PMCID: PMC10767640 PMID: 38175662

Key Points

Question

Is hearing loss associated with incident dementia among people using and not using hearing aids?

Findings

In this cohort study that included 573 088 persons, hearing loss was significantly associated with a 7% higher risk of dementia. People with hearing loss who were not using hearing aids were at considerably higher risk of dementia compared with people with hearing loss who used hearing aids.

Meaning

The study results suggest that hearing aids may prevent or delay the onset and progression of dementia.

Abstract

Importance

Hearing loss has been suggested as a risk factor for dementia, but there is still a need for high-quality research to better understand the association between these 2 conditions and the underlying causal mechanisms and treatment benefits using larger cohorts and detailed data.

Objective

To investigate the association between hearing loss and incident dementia, as well as how hearing aid use contributes to this association.

Design, Setting, and Participants

This population-based cohort study was conducted in Southern Denmark between January 2003 and December 2017 and included all residents 50 years and older. We excluded all persons with dementia before baseline as well as those who did not live in the region 5 years before baseline, with incomplete address history, or who had missing covariate information.

Exposures

Individual hearing status based on the Hearing Examinations in Southern Denmark database, which contains data on all pure-tone audiometry examinations performed at public hearing rehabilitation clinics in Southern Denmark.

Main Outcomes and Measures

Incident cases of dementia and Alzheimer disease as identified from national registries.

Results

The study population comprised 573 088 persons (298 006 women [52%]; mean [SD] age, 60.8 [11.3] years) with 23 023 cases of dementia and mean (SD) follow-up of 8.6 (4.3) years. Having a hearing loss was associated with an increased risk of dementia, with an adjusted hazard ratio (HR) of 1.07 (95% CI, 1.04-1.11) compared with having no hearing loss. Severe hearing loss in the better and worse ear was associated with a higher dementia risk, with an HR of 1.20 (95% CI, 1.09-1.32) and 1.13 (95% CI, 1.06-1.20), respectively, compared with having no hearing loss in the corresponding ear. Compared with people without hearing loss, the risk of dementia was higher among people with hearing loss who were not using hearing aids than those who had hearing loss and were using hearing aids, with HRs of 1.20 (95% CI, 1.13-1.27) and 1.06 (95% CI, 1.01-1.10), respectively.

Conclusions and Relevance

The results of this cohort study suggest that hearing loss was associated with increased dementia risk, especially among people not using hearing aids, suggesting that hearing aids might prevent or delay the onset and progression of dementia. The risk estimates were lower than in previous studies, highlighting the need for more high-quality longitudinal studies.

This cohort study examines the association between hearing loss and incident dementia as well as how hearing aid use contributes to this association.

Introduction

The world is currently facing a concerning rise in the number of people with diagnoses of dementia,¹ primarily due to an aging population. However, the literature suggests that other risk factors, such as physical inactivity, smoking, and diet, also play a role.^1,2,3,4 Hearing loss (HL) has also been suggested as a risk factor for dementia, since previous studies have found an association of impaired hearing function with cognitive decline and dementia.^3,4,5,6,7 Proposed mechanisms include an association of HL with cognitive load and reallocation of cortical resources toward auditory processing, hampering other cognitive processes, reduced social interaction and decreased stimulation due to HL, and a possible common underlying pathology for both conditions.^5,8,9,10

Most existing studies on HL and dementia/cognition are cross-sectional, precluding conclusions on temporality and causality.^6,7 Moreover, the existing studies applied different adjustment strategies and definitions of HL, dementia, and cognitive decline.^5,6,7 The few longitudinal studies produced results ranging from no or weak associations^11,12,13,14 to very strong associations between HL and dementia.^15,16,17 The Lancet commission on dementia prevention ranked HL as the most important modifiable risk factor for dementia due to its elevated prevalence and high pooled risk estimates.^3,4 However, this meta-analysis was only based on 3 longitudinal studies of limited population sizes (ie, 639,¹⁵ 1057,¹⁶ and 2034¹⁸ persons).

If HL is confirmed as a risk factor for dementia, rehabilitation methods (eg, hearing aids) might prevent or delay the onset and progression of dementia. However, recent reviews emphasize the lack of evidence on this topic.^3,4,6,7,8 Therefore, there is still a need for studies based on larger cohorts with comprehensive data on HL and potential confounders to elucidate the associations of HL, dementia, and hearing aid use.

We aimed to investigate associations between HL and incident dementia as well as the contribution of hearing aids to these associations, in a population-based cohort of all adults 50 years or older living in Southern Denmark between 2003 and 2017. The study was based on detailed audiometric hearing information from public hearing rehabilitation clinics together with register-based data on dementia and several covariates.

Methods

Study Population

The Danish administrative region Southern Denmark has a population of 1.23 million people.¹⁹ Using residency information from the Building and Housing Register,²⁰ we identified all addresses in this region and linked them to the Civil Registration System.²¹ We established a study base of all adults 50 years or older who were living in this region from January 1, 2003, to December 31, 2017. We used residents’ unique personal identification number²¹ to establish complete address histories and follow them across health and administrative registers. This study was approved by local authorities (record number: 2018-DCRC-0055) and followed the Strengthening the Reporting of Observational Studies in Epidemiology (STROBE) reporting guidelines for cohort studies. The use of the Hearing Examinations in Southern Denmark (HESD) database was approved by the Danish Patient Safety Authority. By Danish law, the use of Danish national registers does not require patient consent and approval from ethical committees.

Hearing Assessment

Hearing information was extracted from the HESD database.²² This database contains information of all pure-tone audiometry examinations conducted at 3 state-funded clinics in this region, corresponding to data for approximately 145 000 patients. We derived 3 variables to assess individual hearing status: (1) pure-tone averages (PTAs) across thresholds measured at 0.5, 1, 2, and 4 kHz that were calculated for the better and worse ear; (2) HL yes/no, with HL present when a threshold was higher than 20 dBHL in the better ear at any frequency used to calculate the PTA; (3) HL severity based on PTA (ie, normal hearing [≤25 dBHL], mild [26–40 dBHL], moderate [41-60 dBHL], or severe [>60 dBHL]).²³

To extract information on hearing aid use, we retrieved data from the Regional Hearing Aid database and the Battery database, which respectively contain regional-level information on all persons who have requested a subsidy for purchasing hearing aids (either by receiving a refund after buying hearing aids or getting hearing aids directly from the public system [data from 2007]) or subsidized hearing aid batteries (from 2013). Therefore, these persons were considered to be hearing aid users, and even if they had no data recorded in the HESD database, we assumed they most likely had HL. To identify other people with potential HL, we gathered data on all persons with an HL diagnosis in the National Patient Register²⁴ and all persons who underwent an audiometry examination or hearing aid fitting test in private ear, nose, and throat clinics from 1998 to 2018 using data from the National Health Service Register.²⁵ We grouped all persons who fulfilled at least 1 of the 3 criteria (ie, request of hearing aid subsidy/batteries, HL in the patient register, or audiometric examinations in a private clinic) but without any hearing information in HESD as suspected HL, because, although each criterion may indicate HL, we were not able to determine HL with similar validity as for the persons in HESD.

Individuals without any data recorded in HESD (ie, never had an audiogram recorded in the public Danish health system) and that were not classified as having suspected HL were considered to have normal hearing.

Dementia Identification

We identified incident dementia cases from the National Patient Register and the National Prescription Register^24,26 as the first inpatient or outpatient hospital contact (International Classification of Diseases, Eighth Revision [ICD-8] and ICD-10 codes: eTable 1 in Supplement 1) or the first redeemed prescription for an antidementia drug (rivastigmine, donepezil, memantine, or galantamine). For analysis on Alzheimer disease, we used the corresponding ICD codes (eTable 1 in Supplement 1).

Covariates

Covariates were selected based on the existing literature, theoretical plausibility, and availability. Through linkage with Statistics Denmark, we gathered individual-level information on cohabiting status (yes, no); highest attained education, stratified as (1) mandatory school (duration of 10 years), (2) secondary school, vocational school, or other short further education after high school (usual duration of 2-5 years), (3) medium-term and long-term higher education (usual duration of 3-8 years), or (4) unknown; income (based on quintiles and later categorized as low (quartile [Q] 1), medium (Q2-Q4), and high (Q5); country of origin (Denmark, other countries); and occupational status (blue collar, white collar, unemployed, or retired). We also collected area-level socioeconomic variables (ie, percentage of the population with a low income, only basic education, and a criminal record) based on the 2160 parishes in Denmark.²⁷ Using the National Patient Register,²⁴ we collected data on diagnoses (yes/no) for cardiometabolic diseases (diabetes, stroke, ischemic heart diseases, and heart failure).

Statistical Analysis

To ensure that persons had lived at least 5 years in the region before collection of HESD data started, we started follow-up in January 2003 or 2008 (according to participants’ residence location, since HESD data collection at each clinic did not start in the same year) or age 50 years, whichever came last. These 2 baseline dates were chosen because hearing data collection started in different years (1998 or 2003) for each of the regional clinics. Cohort members were followed up until dementia diagnosis (event), death, moving away from Southern Denmark, or December 31, 2017, whichever came first. We excluded all persons with (1) dementia before baseline, (2) an incomplete address history or who did not live in the region 5 years before baseline (to reduce exposure misclassification), or (3) missing information on covariates.

We used Cox proportional hazards models with age as underlying time scale to calculate hazard ratios (HRs) between HL and incident dementia, with HL being assessed in either 3 (yes/no/suspected) or 5 categories (HL severity was calculated for the better and worse ears, thus consisting of 2 independent variables). Persons with suspected HL could change from having suspected HL to confirmed HL (ie, HL = yes) in case any audiogram that met the criteria for HL (as defined previously) was obtained for that person later in time. From the time of the first audiogram, HL was included either as a time-constant (determined from the first audiogram) or time-varying variable (changing with each recorded audiogram). Associations were assessed in 2 models: model 1, which was adjusted for calendar year and sex, and model 2, which was further adjusted for time-varying information on previously described covariates. For analyses based on HL yes/no, we considered HL present for all persons with suspected HL in the Danish registers (ie, record for HL diagnosis and/or audiometric examinations in private clinics) and who also requested a hearing aid subsidy/batteries.

We conducted a sensitivity analysis with right censoring at age 80 years. We also calculated HRs between HL and Alzheimer disease (with censoring for any other dementia). For patients with audiograms, we examined the shape of exposure-response curves between HL and dementia using natural cubic splines with 4 degrees of freedom, based on continuous PTA in the better ear (for model 2).

We conducted a stratified analysis on a smaller subset of data (from 2010, due to data availability) to evaluate whether hearing aid treatment was associated with reduced risk of dementia among people with HL. We assumed hearing aid use from the first request for a hearing aid subsidy and/or batteries, until censoring. Analyses were conducted in SAS, version 9.4 (SAS Institute), and R, version 3.6.3 (R Foundation).

Results

Of the 645 540 persons in the study base, we excluded 7148 persons who received a diagnosis of dementia before baseline, 63 177 with incomplete address history or who did not live in the region 5 years before baseline, and 2127 who had missing covariate information. The final study population comprised 573 088 persons, with 23 023 cases of dementia and a median follow-up of 10 years (range, 0.25 to 15.0 years).

Table 1 shows baseline demographic characteristics according to HL status at the start of follow-up. In general, persons with HL were more likely to be older, men, retired, and with a lower income and education level. The demographic characteristics for the study subpopulation (ie, from 2010) are shown in eTable 2 in Supplement 1.

Table 1. Baseline Characteristics of the Study Population According to HL Status at the Start of Follow-Up.

Baseline characteristic	Entire population (N = 573 088)	With HL (n = 41 104)^a	Without HL (n = 470 667)^a	With suspected HL (n = 61 317)
Sex, %
Female	52.0	43.9	52.9	49.8
Male	48.0	56.1	47.1	50.2
Age, mean (SD), y	60.8 (11.3)	71.4 (12.3)	59.6 (10.5)	63.3 (12.2)
Country of origin, %
Denmark	98.4	98.2	98.4	98.0
Other countries	1.6	1.8	1.6	2.0
Cohabiting status, %
Yes	72.9	64.4	73.8	71.5
No	27.1	35.6	26.2	28.5
Individual income, %^b
Low (Q1)	20.5	30.6	19.4	22.3
Medium (Q2-Q4)	57.0	57.6	56.9	57.2
High (Q5)	22.5	11.8	23.7	20.5
Occupational status, %
Blue collar	30.5	12.9	32.7	25.3
White collar	21.9	8.4	23.4	19.2
Unemployed	3.2	1.6	3.4	3.0
Retired	44.4	77.1	40.5	52.5
Highest attained education, %
Mandatory education	37.1	42.0	36.8	36.9
Secondary or vocational education	42.3	32.9	43.3	40.9
Medium or long education	15.8	10.3	16.3	15.0
Unknown	4.8	14.8	3.6	7.2
Area-level factors, mean (SD)
Percentage of the population with low income (first quartile)	4.6 (2.1)	4.6 (2.0)	4.6 (2.1)	4.7 (2.0)
Percentage of the population with only basic education	10.8 (2.8)	11.1 (2.7)	10.8 (2.8)	10.9 (2.9)
Percentage of the population with criminal record	0.4 (0.3)	0.4 (0.3)	0.4 (0.3)	0.4 (0.3)

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Abbreviations: HL, hearing loss; Q, quartile.

^{^a}

HL = 1 when fulfilling any of the 2 conditions: (1) hearing threshold was higher than 20 dBHL in the better ear at any of the following frequencies: 0.5, 1, 2, and 4 kHz; or (2) the person was identified with a potential HL in the Danish registers (ie, record for HL diagnosis and/or audiometric examinations in private clinics) and also requested a hearing aid subsidy or batteries. HL was determined at baseline.

^{^b}

Based on quintiles.

Having HL was associated with a higher risk of dementia, with an HR of 1.07 (95% CI, 1.04-1.11) compared with having no HL, after adjusting for age (by design), sex, calendar year, cohabiting status, education, income, country of origin, occupational status, presence of cardiometabolic diseases, and area-level socioeconomic variables (Table 2). For people with suspected HL, the HR was 1.03 (95% CI, 0.99-1.07). Severe HL as measured in the better and worse ear was associated with a higher dementia risk, with an HR of 1.20 (95% CI, 1.09-1.32) and 1.13 (95% CI, 1.06-1.20), respectively, compared with having no HL. For mild and moderate HL, HRs were closer to null. HRs obtained for time-constant and time-varying HL were generally very similar (Table 2).

Table 2. Associations Between HL and Risk for Incident Dementia for 23 023 Cases.

HL	Time-constant variables^a			Time-varying variables^b
HL	Cases, No.	Model 1, HR (95% CI)^c	Model 2, HR (95% CI)^d	Cases, No.	Model 1, HR (95% CI)^c	Model 2, HR (95% CI)^d
HL (yes/no)^e
No	12 822	1 [Reference]	1 [Reference]	12 812	1 [Reference]	1 [Reference]
Yes	5895	1.08 (1.05-1.12)	1.07 (1.04-1.11)	5905	1.08 (1.04-1.11)	1.07 (1.04-1.11)
Suspected HL^f	4306	1.03 (0.99-1.07)	1.03 (0.99-1.07)	4306	1.03 (0.99-1.07)	1.03 (0.99-1.06)
HL severity (better ear)
No HL	13 289	1 [Reference]	1 [Reference]	13 146	1 [Reference]	1 [Reference]
Mild (26-40 dBHL)	1998	1.05 (1.00-1.10)	1.05 (1.00-1.10)	1418	1.05 (0.99-1.11)	1.05 (1.00-1.11)
Moderate (41-60 dBHL)	2297	1.02 (0.98-1.07)	1.01 (0.97-1.06)	2606	1.02 (0.98-1.07)	1.02 (0.97-1.06)
Severe (>60 dBHL)	452	1.22 (1.11-1.34)	1.20 (1.09-1.32)	866	1.19 (1.11-1.28)	1.17 (1.09-1.25)
Suspected HL^f	4987	1.04 (1.01-1.07)	1.04 (1.00-1.07)	4987	1.04 (1.01-1.08)	1.04 (1.01-1.07)
HL severity (worse ear)^g
No HL	12 922	1 [Reference]	1 [Reference]	12 882	1 [Reference]	1 [Reference]
Mild (26-40 dBHL)	1195	1.06 (1.00-1.12)	1.07 (1.00-1.13)	820	1.08 (1.01-1.16)	1.09 (1.01-1.17)
Moderate (41-60 dBHL)	2708	1.02 (0.98-1.07)	1.02 (0.97-1.06)	2539	1.01 (0.96-1.05)	1.01 (0.96-1.05)
Severe (>60 dBHL)	1211	1.15 (1.08-1.22)	1.13 (1.06-1.20)	1795	1.14 (1.08-1.20)	1.12 (1.07-1.18)
Suspected HL^g	4987	1.04 (1.01-1.08)	1.04 (1.01-1.08)	4987	1.04 (1.01-1.08)	1.04 (1.01-1.08)

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Abbreviations: HL, hearing loss; HR, hazard ratio.

^{^a}

HL was determined by the first audiogram obtained in time.

^{^b}

HL was continuously updated in case new audiograms were recorded within the follow-up period.

^{^c}

Model 1: adjusted for age (by design), sex, and calendar year.

^{^d}

Model 2: adjusted for age (by design), sex, calendar year, cohabiting status, education, income, country of origin, occupational status, presence of cardiometabolic diseases (ie, diabetes, stroke, ischemic heart diseases, and heart failure), and area-level socioeconomic variables (ie, percentage of the population with low income, only basic education, and a criminal record).

^{^e}

HL = 1 when fulfilling any of the 2 conditions: (1) hearing threshold was higher than 20 dBHL in the better ear at any of the following frequencies: 0.5, 1, 2, and 4 kHz; or (2) the person was identified with a suspected HL in the Danish registers (ie, record for HL diagnosis and/or audiometric examinations in private clinics) and also requested a hearing aid subsidy or batteries.

^{^f}

Categorization based on pure-tone averages for the following frequencies: 0.5, 1, 2, and 4 kHz.

^{^g}

A person was labeled with suspected HL when they did not have any hearing data recorded in the Hearing Examinations in Southern Denmark database, and, at the same time, fulfilled at least 1 of the following conditions: (1) an HL diagnosis recorded in the National Patient Register; (2) a record of audiometry examination or hearing aid fitting test in private ear, nose, and throat clinics; or (3) a recorded request of hearing aid subsidy or subsidized hearing aid batteries.

The associations between HL (suspected and confirmed) and Alzheimer disease were stronger compared with the results we found for overall dementia. However, when investigating HL severity, only mild HL was associated with a higher Alzheimer risk (eTable 3 in Supplement 1).

When assessing associations between HL (yes/no) and dementia by age at HL diagnosis, we observed a decrease in HRs as age increased (Table 3). Given potential difficulties in diagnosing dementia for older age groups, we examined associations after censoring people at age 80 years (eTable 4 in Supplement 1). We found slightly higher HRs compared with the main results: for HL (yes/no), the HR was 1.17 (95% CI, 1.10-1.23) and for severe HL at the better ear, the HR was 1.30 (95% CI, 1.05-1.61) compared with having no HL.

Table 3. Associations Between HL and Risk for Incident Dementia by Age at HL Diagnosis^a.

Age at HL diagnosis, y	HL (yes/no)^a
Age at HL diagnosis, y	No. cases^b	HR (95% CI)^c
No HL	12 822	1 [Reference]
≤65	318	1.34 (1.20-1.51)
65-70	510	1.23 (1.13-1.35)
70-75	1017	1.16 (1.09-1.24)
75-80	1517	1.08 (1.02-1.14)
80-85	1468	1.01 (0.95-1.06)
>85	1065	0.93 (0.87-1.00)

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Abbreviations: HL, hearing loss; HR, hazard ratio.

^{^a}

HL = 1 when fulfilling any of the 2 conditions: (1) hearing threshold was higher than 20 dBHL in the better ear at any of the following frequencies: 0.5, 1, 2, and 4 kHz; or (2) the person was identified with a suspected HL in the Danish registers (ie, record for HL diagnosis and/or audiometric examinations in private clinics) and also requested a hearing aid subsidy or batteries.

^{^b}

A total of 23 023 cases were included. Results for suspected HL are not reported, but corresponding HRs were close to null.

^{^c}

The association between the better ear PTA (time-constant variable) and dementia followed a negative exposure-response trend for lower PTA levels (<45 dBHL) and a positive trend for higher PTA levels (>45 dBHL) (Figure, A). When PTA was assessed as a time-varying variable, we found an increase in risk between about 40 and 70 dBHL, after which we observed a leveling off and even a slight decrease in risk (Figure, B). We found that, compared with people without HL, people with HL who did not use hearing aids were at a higher risk of dementia than people with HL who used hearing aids (ie, nonoverlapping CIs), with HRs of 1.20 (95% CI, 1.13-1.27) and 1.06 (95% CI, 1.01-1.10), respectively (Table 4).

Figure. — In panel A, PTA was included as a time-constant variable, whereas in panel B, PTA was included as a time-varying variable. The exposure-response curves were built using natural cubic splines with 4 degrees of freedom, based on continuous PTA in the better ear and after adjusting for age (by design), sex, calendar year, cohabiting status, education, income, country of origin, occupational status, presence of cardiometabolic diseases, and area-level socioeconomic variables. The solid lines represent hazard ratios (HRs), whereas the dashed lines represent 95% CIs.

Table 4. Associations Between HL and Risk for Incident Dementia in 12 650 Cases According to Hearing Aid Use^a^,^b.

Hearing aid use	No. cases^c	HR (95% CI)^d^,^e
No HL diagnosis	8147	1 [Reference]
Nontreated HL (no hearing aid)	1296	1.20 (1.13-1.27)
Treated HL (hearing aid user)^e	3020	1.06 (1.01-1.10)

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Abbreviations: HL, hearing loss; HR, hazard ratio.

^{^a}

Substudy baseline: 2010.

^{^b}

HL = 1 when fulfilling any of the 2 conditions: (1) hearing threshold was higher than 20 dBHL in the better ear at any of the following frequencies: 0.5, 1, 2, and 4 kHz; or (2) the person was identified with a suspected HL in the Danish registers (ie, record for HL diagnosis and/or audiometric examinations in private clinics) and also requested a hearing aid subsidy or batteries.

^{^c}

A total of 15 367 cases were included. Results for suspected HL are not reported, but corresponding HRs were close to null.

^{^d}

^{^e}

Defined by at least 1 request for hearing aid subsidy and/or hearing aid batteries.

Discussion

In this cohort study, we found that HL, when assessed using audiometry and/or register-based information, was associated with increased risk of dementia. However, the magnitude of these associations was lower than most studies in the field. The study results suggested that mainly severe HL seemed to be associated with a higher dementia risk. The risk of dementia in association with HL was higher among people who were not treated with hearing aids compared with people using hearing aids.

In line with the current study, several studies have suggested associations between HL and cognitive abilities and dementia.^5,6,7,28 Based on the corresponding underlying mechanisms,^5,8,9,10 we hypothesized that the better ear hearing ability would best predict how HL affects a patient’s life in different social and cognitively demanding situations. Accordingly, we generally found stronger associations for HL measured at the better ear compared with the worse ear.

We found that HL was associated with a 7% higher risk of dementia, which is a lower increase in risk than observed in most longitudinal studies.⁷ Among these studies, 2 of them stand out, as they found considerably higher risk estimates than the others: Lin et al¹⁵ found associations starting at mild HL (25-40 dBHL) with an HR of 1.89 (95% CI, 1.00-3.58) and HR of 4.94 (95% CI, 3.45-7.08) for severe HL, and Gallacher et al¹⁶ found an HR of 2.67 (95% CI, 1.38-5.17). However, the CIs in these studies were wide due to few dementia cases (58 and 79, respectively). These were 2 of the 3 studies included in The Lancet dementia report,^3,4 which reported a pooled relative risk of dementia due to HL of 1.9. In contrast, other longitudinal studies have shown substantially lower risk estimates.^11,12,13,14 A potential explanation for these diverse results may be associated with the study design and biased cognitive test results, as patients with HL need to be able to hear the interviewer and understand the tasks.⁸ In support, Gallacher et al¹⁶ found stronger associations when cognitive tests were performed in interviews compared with computer-based testing, suggesting that HL disturbs the performance in interview-based tests. This may have contributed to an overestimation of risks, especially in studies in which interview-based cognitive tests were conducted for all participants, as people with HL may thus be more likely to receive a dementia diagnosis.²⁹ Moreover, publication bias within this topic cannot be ruled out.⁷

We found that among people with a diagnosis of HL, HRs among hearing aid users were substantially lower compared with people not using hearing aids, which suggests that hearing aid use could be a tool in preventing or delaying dementia onset. If this is confirmed in future studies, this fact may also explain the lower risk estimates found in Danish studies (both ours and the one by Osler et al³⁰) compared with previous studies, as Denmark is the European country with the highest proportion of hearing aid users among those with self-reported HL.³¹ The estimated proportion (more than 50%) is much higher than the US,³² where most previous longitudinal studies have been conducted.⁷

The few studies that have investigated the benefit of hearing aids on cognitive outcomes have shown inconclusive findings, likely due to methodological limitations, such as small sample sizes,^33,34 short follow-up,³⁵ and a cross-sectional design.³⁶ A recent Korean study³⁷ longitudinally compared dementia incidence among people who received hearing aids subsidies and people who did not, showing that hearing aid use was associated with reduced risk of dementia (HR, 0.75). Although their analyses were controlled for different factors, including age and income, important potential confounders, such as education and cohabiting status, were not considered. In our study, we found that hearing aid users were more likely to have a partner and a longer education. Accordingly, other studies showed that people with these characteristics are more likely to receive and use hearing aids.³⁸

In better agreement with our study, Deal et al¹⁸ observed associations with dementia starting from moderate/severe HL (>40 dBHL). The exposure-response curve illustrating this association was relatively similar to what we found, with an initial plateau for low HL levels followed by a linear upward trend and a slight decrease in risk at the end of the curve. However, the authors found associations for moderate HL, which was not the case in our study. This may potentially be explained by their cohort being limited to persons aged 70 to 79 years. In our study, we observed higher HRs after censoring individuals at age 80 years, which is in agreement with our results for different age groups, showing stronger associations among people with a diagnosis of HL earlier in life. A potential explanation for this pattern is that people who get a diagnosis of HL at younger ages are more likely to have HL that is caused by hereditary factors. These patients are likely to have lived with their HL for years, which may have affected their cognition for a longer period and during a stage of life when listening can have a higher effect in daily activities (eg, work routine and a more intense social life). In contrast, a Danish study that was also based on dementia identified through national registers found no differences in HRs between those who received a diagnosis of HL when younger or older than 50 years.³⁰ However, the authors did not inspect other age groups.

In a subanalysis investigating associations between HL and Alzheimer disease, we observed higher HRs for people with a suspected HL compared with those with a confirmed HL and only positive associations for mild HL when investigating HL severity. The few longitudinal studies on this also show conflicting findings.^6,7,15,17 As dementia, including Alzheimer disease, and HL often coexist, families may confuse communication difficulties with cognition difficulties instead of recognizing it as a hearing problem. If this is the case, then exposure (ie, HL) misclassification can be differential (ie, higher among cases than noncases), which can bias the risk estimates away from the null and potentially explain these unexpected findings.³⁹ This is more likely to happen when HL is not so severe, which may explain why HRs for Alzheimer disease and mild HL were considerably higher than for moderate and severe HL.

Strengths and Limitations

This study’s limitations included outcome misclassification, as our study was based on register-based dementia diagnosis and therefore did not consider different degrees of dementia and cognitive decline. Nevertheless, researchers demonstrated a high validity for diagnoses extracted from Danish registers, especially for all-cause dementia.⁴⁰ Exposure (ie, HL status) misclassification may have also affected the results, especially because the exact onset time of HL or trajectory of worsening for many persons is unknown.⁴¹ Moreover, the likelihood for undiagnosed HL is higher when HL is less severe. This could contribute to the null HRs observed for moderate HL. We also departed from the premise that those without an audiogram had normal hearing. This is likely not the case for everyone, since survey studies have shown that many people underestimate their hearing impairment.^42,43 Furthermore, we cannot be sure that those who received subsidized hearing aids or batteries were using their hearing aids on a regular basis. However, we can be sure that all persons who were granted a subsidy received hearing aids, and we can also presume that those who requested batteries are frequent users.

A main strength of our study is the large population-based prospective design, with a more representative study population than many previous studies, which included smaller cohorts based on volunteers,¹⁵ only men,³⁰ or people within a specific age range.¹⁸ Another strength was the use of pure-tone audiometry, enabling for a detailed assessment of HL severity and time-varying information for a large part of the population. However, the method is not able to assess auditory processing and individual abilities to understand speech and language input, which are proposed to be key factors on the underlying mechanisms between dementia and HL.^9,29 A third strength was the inclusion of several factors that could confound the association between HL and dementia, such as demographic information, comorbidities, and individual and area-level socioeconomic status.

Conclusions

In this cohort study, we found an association between HL and risk of dementia, especially among people who did not use hearing aids. Although the clinical relevance of these findings is still unclear, the study results suggest that treatment of HL with hearing aids may be associated with reduced risk of dementia, which calls for a better understanding of the association between HL and dementia as a critical step for the development of prevention strategies. Although we found that HL was associated with increased risk of dementia, the increase in risk observed was considerably lower than in previous studies, highlighting the need for more high-quality longitudinal studies so that the clinical relevance of this association can be determined.

Supplement 1.

eTable 1. International Classification of Diseases (ICD)-8 and ICD-10 codes used to identify dementia diagnosis

eTable 2. Study sub-population’s characteristics at baseline, for a smaller subset of data

eTable 3. Associations between hearing loss (time-constant) and risk for incident Alzheimer’s disease

eTable 4. Associations between hearing loss (time-constant) and risk for incident dementia

Click here for additional data file.^{(273.8KB, pdf)}

Supplement 2.

Data sharing statement

Click here for additional data file.^{(15.9KB, pdf)}

References

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Associated Data

This section collects any data citations, data availability statements, or supplementary materials included in this article.

Supplementary Materials

Supplement 1.

eTable 1. International Classification of Diseases (ICD)-8 and ICD-10 codes used to identify dementia diagnosis

eTable 2. Study sub-population’s characteristics at baseline, for a smaller subset of data

eTable 3. Associations between hearing loss (time-constant) and risk for incident Alzheimer’s disease

eTable 4. Associations between hearing loss (time-constant) and risk for incident dementia

Click here for additional data file.^{(273.8KB, pdf)}

Supplement 2.

Data sharing statement

Click here for additional data file.^{(15.9KB, pdf)}

[ooi230074r1] 1.GBD 2019 Dementia Forecasting Collaborators . Estimation of the global prevalence of dementia in 2019 and forecasted prevalence in 2050: an analysis for the Global Burden of Disease Study 2019. Lancet Public Health. 2022;7(2):e105-e125. doi: 10.1016/S2468-2667(21)00249-8 [DOI] [PMC free article] [PubMed] [Google Scholar]

[ooi230074r2] 2.World Health Organization . Risk reduction of cognitive decline and dementia: WHO guidelines. Accessed November 25, 2022. https://www.who.int/publications/i/item/9789241550543 [PubMed]

[ooi230074r3] 3.Livingston G, Sommerlad A, Orgeta V, et al. Dementia prevention, intervention, and care. Lancet. 2017;390(10113):2673-2734. doi: 10.1016/S0140-6736(17)31363-6 [DOI] [PubMed] [Google Scholar]

[ooi230074r4] 4.Livingston G, Huntley J, Sommerlad A, et al. Dementia prevention, intervention, and care: 2020 report of the Lancet Commission. Lancet. 2020;396(10248):413-446. doi: 10.1016/S0140-6736(20)30367-6 [DOI] [PMC free article] [PubMed] [Google Scholar]

[ooi230074r5] 5.Thomson RS, Auduong P, Miller AT, Gurgel RK. Hearing loss as a risk factor for dementia: a systematic review. Laryngoscope Investig Otolaryngol. 2017;2(2):69-79. doi: 10.1002/lio2.65 [DOI] [PMC free article] [PubMed] [Google Scholar]

[ooi230074r6] 6.Loughrey DG, Kelly ME, Kelley GA, Brennan S, Lawlor BA. Association of age-related hearing loss with cognitive function, cognitive impairment, and dementia a systematic review and meta-analysis. JAMA Otolaryngol Head Neck Surg. 2018;144(2):115-126. doi: 10.1001/jamaoto.2017.2513 [DOI] [PMC free article] [PubMed] [Google Scholar]

[ooi230074r7] 7.Liang Z, Li A, Xu Y, Qian X, Gao X. Hearing loss and dementia: a meta-analysis of prospective cohort studies. Front Aging Neurosci. 2021;13:695117. doi: 10.3389/fnagi.2021.695117 [DOI] [PMC free article] [PubMed] [Google Scholar]

[ooi230074r8] 8.Amieva H, Ouvrard C. Does treating hearing loss in older adults improve cognitive outcomes? a review. J Clin Med. 2020;9(3):1-12. doi: 10.3390/jcm9030805 [DOI] [PMC free article] [PubMed] [Google Scholar]

[ooi230074r9] 9.Griffiths TD, Lad M, Kumar S, et al. How can hearing loss cause dementia? Neuron. 2020;108(3):401-412. doi: 10.1016/j.neuron.2020.08.003 [DOI] [PMC free article] [PubMed] [Google Scholar]

[ooi230074r10] 10.Lin FR, Albert M. Hearing loss and dementia—who is listening? Aging Ment Health. 2014;18(6):671-673. doi: 10.1080/13607863.2014.915924 [DOI] [PMC free article] [PubMed] [Google Scholar]

[ooi230074r11] 11.Gurgel RK, Ward PD, Schwartz S, Norton MC, Foster NL, Tschanz JT. Relationship of hearing loss and dementia: a prospective, population-based study. Otol Neurotol. 2014;35(5):775-781. doi: 10.1097/MAO.0000000000000313 [DOI] [PMC free article] [PubMed] [Google Scholar]

[ooi230074r12] 12.Amieva H, Ouvrard C, Meillon C, Rullier L, Dartigues JF. Death, depression, disability, and dementia associated with self-reported hearing problems: a 25-year study. J Gerontol A Biol Sci Med Sci. 2018;73(10):1383-1389. doi: 10.1093/gerona/glx250 [DOI] [PubMed] [Google Scholar]

[ooi230074r13] 13.Brenowitz WD, Kaup AR, Lin FR, Yaffe K. Multiple sensory impairment is associated with increased risk of dementia among black and white older adults. J Gerontol A Biol Sci Med Sci. 2019;74(6):890-896. doi: 10.1093/gerona/gly264 [DOI] [PMC free article] [PubMed] [Google Scholar]

[ooi230074r14] 14.Brewster KK, Hu MC, Zilcha-Mano S, et al. Age-related hearing loss, late-life depression, and risk for incident dementia in older adults. J Gerontol A Biol Sci Med Sci. 2021;76(5):827-834. doi: 10.1093/gerona/glaa242 [DOI] [PMC free article] [PubMed] [Google Scholar]

[ooi230074r15] 15.Lin FR, Metter EJ, O’Brien RJ, Resnick SM, Zonderman AB, Ferrucci L. Hearing loss and incident dementia. Arch Neurol. 2011;68(2):214-220. doi: 10.1001/archneurol.2010.362 [DOI] [PMC free article] [PubMed] [Google Scholar]

[ooi230074r16] 16.Gallacher J, Ilubaera V, Ben-Shlomo Y, et al. Auditory threshold, phonologic demand, and incident dementia. Neurology. 2012;79(15):1583-1590. doi: 10.1212/WNL.0b013e31826e263d [DOI] [PubMed] [Google Scholar]

[ooi230074r17] 17.Golub JS, Luchsinger JA, Manly JJ, Stern Y, Mayeux R, Schupf N. Observed hearing loss and incident dementia in a multiethnic cohort. J Am Geriatr Soc. 2017;65(8):1691-1697. doi: 10.1111/jgs.14848 [DOI] [PMC free article] [PubMed] [Google Scholar]

[ooi230074r18] 18.Deal JA, Betz J, Yaffe K, et al. ; Health ABC Study Group . Hearing impairment and incident dementia and cognitive decline in older adults: the health ABC study. J Gerontol A Biol Sci Med Sci. 2017;72(5):703-709. doi: 10.1093/gerona/glw069 [DOI] [PMC free article] [PubMed] [Google Scholar]

[ooi230074r19] 19.Statistics Denmark . StatBank Denmark [internet]. Accessed November 15, 2022. https://statistikbanken.dk/statbank5a/default.asp?w=1920

[ooi230074r20] 20.Christensen G. The building and housing register. Scand J Public Health. 2011;39(7)(suppl):106-108. doi: 10.1177/1403494811399168 [DOI] [PubMed] [Google Scholar]

[ooi230074r21] 21.Schmidt M, Pedersen L, Sørensen HT. The Danish Civil Registration System as a tool in epidemiology. Eur J Epidemiol. 2014;29(8):541-549. doi: 10.1007/s10654-014-9930-3 [DOI] [PubMed] [Google Scholar]

[ooi230074r22] 22.Cantuaria ML, Pedersen ER, Waldorff FB, Sørensen M, Schmidt JH. Hearing examinations in Southern Denmark (HESD) database: a valuable tool for hearing-related epidemiological research. Int J Audiol. 2021;60(4):300-311. doi: 10.1080/14992027.2020.1831702 [DOI] [PubMed] [Google Scholar]

[ooi230074r23] 23.Garg S, Kohli C, Mangla V, Chadha S, Singh MM, Dahiya N. An epidemiological study on burden of hearing loss and its associated factors in Delhi, India. Ann Otol Rhinol Laryngol. 2018;127(9):614-619. doi: 10.1177/0003489418781968 [DOI] [PubMed] [Google Scholar]

[ooi230074r24] 24.Lynge E, Sandegaard JL, Rebolj M. The Danish national patient register. Scand J Public Health. 2011;39(7)(suppl):30-33. doi: 10.1177/1403494811401482 [DOI] [PubMed] [Google Scholar]

[ooi230074r25] 25.Andersen JS, Olivarius NdeF, Krasnik A. The Danish national health service register. Scand J Public Health. 2011;39(7)(suppl):34-37. doi: 10.1177/1403494810394718 [DOI] [PubMed] [Google Scholar]

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PERMALINK

Hearing Loss, Hearing Aid Use, and Risk of Dementia in Older Adults

Manuella Lech Cantuaria, PhD

Ellen Raben Pedersen, PhD

Frans Boch Waldorff, MD, PhD

Lene Wermuth, MD

Kjeld Møller Pedersen, PhD

Aslak Harbo Poulsen, PhD

Ole Raaschou-Nielsen, PhD

Mette Sørensen, PhD

Jesper Hvass Schmidt, MD, PhD

Key Points

Question

Findings

Meaning

Abstract

Importance

Objective

Design, Setting, and Participants

Exposures

Main Outcomes and Measures

Results

Conclusions and Relevance

Introduction

Methods

Study Population

Hearing Assessment

Dementia Identification

Covariates

Statistical Analysis

Results

Table 1. Baseline Characteristics of the Study Population According to HL Status at the Start of Follow-Up.

Table 2. Associations Between HL and Risk for Incident Dementia for 23 023 Cases.

Table 3. Associations Between HL and Risk for Incident Dementia by Age at HL Diagnosisa.

Figure. Exposure-Response Association Between Better Ear Pure-Tone Average (PTA) and Hazard Ratios for Dementia.

Table 4. Associations Between HL and Risk for Incident Dementia in 12 650 Cases According to Hearing Aid Usea,b.

Discussion

Strengths and Limitations

Conclusions

References

Associated Data

Supplementary Materials

ACTIONS

PERMALINK

RESOURCES

Similar articles

Cited by other articles

Links to NCBI Databases

Table 3. Associations Between HL and Risk for Incident Dementia by Age at HL Diagnosis^a.

Table 4. Associations Between HL and Risk for Incident Dementia in 12 650 Cases According to Hearing Aid Use^a^,^b.