Use of hearing aids by people with a hearing loss can significantly reduce their risk of dementia. People with hearing loss who do not use a hearing aid could have a higher risk of dementia compared to people without hearing loss, according to a study published April 14 (23:30 UK Time on April 13) in the journal The Lancet Public Health.
The study said that when people with hearing loss use a hearing aid, their dementia risk could be reduced to the same level as people without hearing loss.
Link between dementia and hearing loss
Older adults often experience dementia and hearing loss. According to the Lancet Commission on dementia prevention, intervention and care published in 2020, hearing loss may be associated with around 8 per cent of worldwide dementia cases. This implies that one of the most significant ways to reduce the global burden of dementia is to address hearing loss.
In a statement released by The Lancet, Professor Dongshan Zhu from Shandong University, and corresponding author on the paper, said there is increasing evidence that hearing loss may be the most impactful modifiable risk factor for dementia in mid-life. However, the effectiveness of hearing aid use on reducing the risk of dementia in the real world has remained unclear.
Significance of the new study
The new study is significant because it provides the best evidence to date to suggest that hearing aids could be a minimally invasive, cost-effective treatment to mitigate the potential impact of hearing loss on dementia.
How the study was conducted
As part of the study, the authors looked at data from 4,37,704 people who were part of the UK Biobank database. The researchers collected information on the presence of hearing loss and the use of hearing aids through self-reported questionnaires, and determined dementia diagnoses using hospital records and death register data. The average age of the study participants at recruitment was 56 years.
Proportions of people with hearing loss, and proportions of people using hearing aid
The study found that around three-quarters of the participants, which amounted to 3,25,882 people, had no hearing loss, and the remaining one-quarter, which amounted to 1,11,822 people, had some level of hearing loss.
The percentage of people with hearing loss using hearing aids was 11.7, which amounted to 13,092 people.
Risk of dementia in people with hearing loss not using hearing aids
The authors found that compared to participants with normal hearing, people with hearing loss not using hearing aids had a 42 per cent higher risk of all-cause dementia. Meanwhile, people with hearing loss using hearing aids had no increased risk of dementia.
People with hearing loss who are not using hearing aids are at a 1.7 per cent risk of dementia, while people without hearing loss, or those experiencing hearing loss using a hearing aid are at a 1.2 per cent risk of dementia.
Dongshan Zhu said that about four-fifths of people experiencing hearing loss do not use hearing aids in the United Kingdom. He further said that hearing loss may begin early in one's 40s, and there is evidence that gradual cognitive decline before a dementia diagnosis can last 20 to 25 years.
What message does the study provide?
The study highlights the urgent need for the early introduction of hearing aids to people who have started experiencing hearing impairment.
The society also has the responsibility of making a group effort, by raising awareness of hearing loss and its association with dementia, reducing the cost of hearing aids to increase their accessibility, provide more support to primary care workers to screen for hearing impairment, and deliver treatment such as fitting hearing aids, according to Dongshan Zhu.
Do hearing aids provide protection from increased dementia due to indirect causes?
Other factors such as loneliness, depressive symptoms and social isolation might impact the link between hearing loss and dementia. The authors analysed these factors, and found that less than eight per cent of the association between hearing aid use and decreased dementia risk could be removed by improving psychosocial problems. This indicates the fact that the association between hearing aid use and protection from increased dementia is likely mostly due to direct effects from hearing aids rather than the investigated indirect causes.
Dr Fan Jiang from Shandong University, and one of the authors on the paper, said the underlying pathways which may link hearing aid use and reduced dementia risk are unclear, and therefore, further research is needed to establish a causal relationship and the presence of underlying pathways.
Limitations to the study
The authors noted some limitations to the study, including the fact that self-reporting of hearing loss problems and the use of hearing aid is at risk of bias, and since the study is observational, the association between hearing loss and dementia could be due to reverse causation through neurodegeneration or other shared mechanisms. This means that dementia may also trigger hearing loss.
Another limitation to the study was that the authors did not take into consideration some factors such as those who used hearing aids potentially taking more care of themselves compared to those who did not use hearing aids.
The authors also said that most of the participants are white, and very few participants were born deaf or experienced hearing loss before acquiring spoken language, which may limit the extent to which the findings could be generalised to other ethnicities, and also to the people with limited hearing or hearing loss who use sign language.