Do Hearing Aids Reduce Dementia, or Does Dementia Reduce Hearing Aid Use?

The publication of the Lancet Commission Report on Dementia prevention, intervention, and care in 2017 brought hearing loss into the spotlight as a leading potentially modifiable risk factor for late-life dementia. 1 How hearing loss can accelerate decline into dementia remains a subject of debate; several possible mechanisms have been suggested, and more than one may be involved. 2www.shutterstock.com. Dementia, hearing aids, cognitive decline.Figure 1: Study sample selection of cognitively healthy participents to evaluate whether hearing aid use persistence impacts the odds of receiving a dementia diagnosis 3.5 to 5.0 years later. Abbreviations: HA, hearing aid; MCI, mild cognitive impairment. Dementia, hearing aids, cognitive decline.Figure 2: Study sample selection of participants to evaluate whether a diagnosis of dementia prior to a hearing aid fitting impacts the odds of persistent hearing aid use 3+ years later. Dementia, hearing aids, cognitive decline.In any case, if the use of hearing aids protects against cognitive decline, then this would be a strong argument for more widespread screening of hearing and earlier provision of hearing aids. Given the rising numbers of elderly (the group at highest risk for dementia) and the high cost of dementia care, there is a pressing case for finding cost-effective means of minimizing the burden of dementia. This possibility has evoked much hype in the hearing aid industry, among audiologists, and in the field of dementia research. Further, newspaper and magazine articles have made the general public aware of this too, which has led to the potentially misleading message: Get hearing aids to prevent dementia. 3 The Lancet Commission’s latest report estimated that if mid-life (i.e. age-related) hearing loss were eliminated, there would be eight percent fewer cases of dementia. 4 However, there is no medical cure for hearing loss, and the primary intervention (hearing aids) is neither 100% effective at alleviating hearing difficulties, nor taken up by the majority of people who could benefit from it. As of yet, no robust and well-powered randomized controlled trial has been completed to establish whether sustained hearing aid use is protective against dementia, and most evidence is either cross-sectional rather than longitudinal, or poorly controlled for confounding effects. An especially important confound arises because people who are on a path of cognitive decline find ordinary everyday tasks increasingly challenging. They will be likely to find hearing aid use and maintenance correspondingly burdensome, and thus stop using the devices. In cross-sectional data, or longitudinal data without adequately controlled variables, an association between device use and dementia (where more device use = less dementia) could be due to hearing aids protecting against dementia, or dementia causing disuse of hearing aids — or a combination of both. So, it is critical that the relationships between dementia and hearing aid use be disentangled. Our research, supported by the UK’s Medical Research Council, the UK’s National Institute for Health and Care Research, and the U.S. Department of Veterans Affairs, and published in Age & Ageing, has shown that both mechanisms probably coexist. 5 The results highlight the need for caution in interpreting cross-sectional studies of associations between hearing aid use and dementia incidence. They also show that any protective effect of hearing aid use against dementia will not be fully realized unless the devices and associated care processes are themselves “dementia-friendly.” STUDY METHOD AND RESULTS The study sampled 380,794 U.S. veterans 60 years or older who had obtained hearing aids in 2012-2014 from the Department of Veterans Affairs. We analyzed their longitudinal electronic health care records from 2007 up to 2017, thus accessing aspects of health before and after treatment for hearing loss. Having access to these health data allowed us to control for demographic and health-related confounders relevant to hearing loss and cognitive impairment and therefore, results can be interpreted as being generally independent of those factors. Uniquely, longitudinal records of battery orders were used to measure long-term persistent hearing aid use. 6 First, selecting only cognitively healthy patients without diagnoses of dementia or mild cognitive impairment prior to hearing aid fitting, and splitting them according to whether they remained persistent users over two years later, we showed that persistent hearing aid use was associated with a reduction in the odds of receiving a dementia diagnosis 3.5 to 5 years later by about 27%. Second, when comparing patients who had a dementia diagnosis prior to their hearing aid fitting against those who remained cognitively healthy throughout the 11-year period for which data were available, we found that those with pre-existing dementia had 54% reduced odds of being persistent hearing aid users three or more years after receiving their hearing aids. Figures 1 and 2 explain patient selection for the patient samples used for each of these two comparisons. CONCLUSIONS This is the first study to combine longitudinal data regarding dementia diagnoses with continuous assessment of hearing aid use in a large patient sample, which allowed us to disentangle relationships between dementia and hearing aid use. Using the same dataset, this study evaluated two hypotheses, 1) that hearing aid use is protective against dementia, and 2) that patients with dementia are less likely to continue using their hearing aids. Evidence supporting both hypotheses was found. Importantly, this is the first study (to our knowledge) to provide quantitative evidence that dementia diagnosis is associated with lower long-term rates of persistent hearing aid use, which reinforces similar findings from qualitative studies and anecdotal evidence from individuals who work with patients with dementia. 7 The takeaways then are that lack of hearing aid use (i.e., untreated hearing problems) can increase the risk of dementia, but also that cognitive impairment can be a factor in the discontinuation of hearing aid use. This raises the possibility of a vicious circle between untreated hearing loss and cognitive decline. Future research investigating relationships -between hearing loss, hearing aid use, and cognitive decline must -account for the effects of cognitive decline itself on continued hearing aid use. Clinically, any potential protective effect of hearing aid use against dementia will be fully achieved only if devices and care processes are usable by and accessible to the target population. To encourage and promote persistent hearing aid use, more dementia-friendly devices and care processes are needed.