Hearing impairment and risk of dementia in The HUNT Study (HUNT4 70+): a Norwegian cohort study.

Background

Hearing impairment is strongly associated with future dementia. No studies have reported objectively measured hearing impairment in a cohort with a long period of follow-up (>20 years), and few have reported follow-up over 10 years. Hence, there is a need for high quality studies with sufficient follow-up time and data to account for reverse causality and confounding. We aimed to address this knowledge gap.

Methods

This cohort study used individual participant data from The Trøndelag Health Study (HUNT) in Norway. All current residents aged at least 20 years in the former Norwegian Nord-Trøndelag County were invited to participate in four decennial surveys: HUNT1 (1984-1986), HUNT2 (1995-1997), HUNT3 (2006-2008), and HUNT4 (2017-2019) with individuals aged at least 70 years included in a substudy, known as HUNT4 70+. Here, we report the findings of this substudy. HUNT4 70+ comprised 7135 participants who were assessed for dementia using the Diagnostic and Statistical Manual of Mental Disorders 5 criteria and who had audiometry between 1996 and 1998. The primary objective was to investigate, with gold standard audiometric testing and dementia diagnostic assessment, whether hearing impairment was an independent risk factor for all-cause dementia. The secondary objective was to investigate if a risk also applied to Alzheimer dementia and non-Alzheimer dementia. We analysed the association using Poisson regression and adjusted for confounders. This study is registered with ClinicalTrials.gov (NCT04284384).

Findings

At baseline, 1058 (15%) individuals had acquired hearing impairment with a hearing threshold of at least 25 decibel (dB) and, at follow-up, 1089 (15%) had dementia. In the total group, people with hearing impairment had a relative risk (RR) 1.04 (95% confidence interval (CI) 1.00-1.09) per 10 dB increase in hearing thresholds. For individuals younger than 85 years at follow-up the RR was 1.12 (95% CI 1.05-1.21). Associations between hearing impairment and Alzheimer dementia and non-Alzheimer dementia were similar. There was no association for individuals aged at least 85 years.

Interpretation

We found a moderate association between objectively measured hearing impairment and dementia in the younger age group (<85 years). The findings of no association in the older age group (≥85 years) might be due to the competing risk of death. The present study adds to the literature showing that acquired hearing impairment is a risk for dementias over a period which is too long for reverse causation, and with thorough consideration of confounders. Further research is needed to investigate associations between the different aetiologies of hearing loss and dementia subtypes, and risk differences for sexes.

Funding

The Norwegian National Centre for Ageing and Health with a grant from Health South-East.

Informations de copyright

© 2023 The Authors.

Déclaration de conflit d'intérêts

SGC has in the last 36 months received grants for research in dementia prevention, including by treating hearing loss, from UK NIHR, grant for dementia risk assessment from Dunhill Medical Trust—UK Charity, and grant for research in dementia prevention, including by treating hearing loss, from Alzheimer’s Research UK—Charity. FL has in the last 36 months received research grants pertaining to hearing loss from National Institutes of Health, research grants pertaining to hearing loss from Eleanor Schwartz Charitable Foundation, consulting fees as consultant on topics related to hearing loss from Frequency Therapeutics and Apple Inc., personal fees as expert witness for the plaintiff in a class action lawsuit against an insurance company in Washington state pertaining to litigation relating to the insurance company’s policy of non-coverage for hearing aids, is a scientific advisory board member for Fondation Pour L’Audition, is a scientific advisory board member (possible stock options pending continued role on the SAB), is a volunteer board of the nonprofit AccessHears, received donation in-kind from Sonova to Johns Hopkins University for hearing technologies used in the NIH-funded ACHIEVE trial, and is director of a public health research center funded in part by a philanthropic donation from Cochlear Ltd., to the Johns Hopkins Bloomberg School of Public Health. GL has since the initial planning of the work received payment made to the institutions University College London Hospitals’ National Institute for Health Research (NIHR), and Biomedical Research Centre, North Thames NIHR Applied Research Collaboration, and as an NIHR Senior Investigator to support academics to work. GS has participated in advisory boards for Biogen, Eisai and Roche concerning antidementia drugs. All other authors declare no competing interests.