Hearing aids might reduce cognitive decline in older adults, but only in people who are at higher risk of dementia, research has suggested.
The study found the devices and audiological support services did not have any impact on cognitive decline over three years in a general population of older adults.
However, treating hearing loss was found to protect against cognitive decline – loss of memory and thinking skills – in older adults at greater risk of dementia.
Researchers said the study highlights the importance of treating hearing loss in older people as a potential way to reduce the global burden of the condition.
Professor Frank Lin, of Johns Hopkins University School of Medicine and Bloomberg School of Public Health in the US, said: “These results provide compelling evidence that treating hearing loss is a powerful tool to protect cognitive function in later life, and possibly, over the long term, delay a dementia diagnosis.
“But any cognitive benefits of treating age-related hearing loss are likely to vary depending on an individuals’ risk of cognitive decline.”
Age-related hearing loss affects two-thirds of adults aged over 60 globally.
But less than 10% of people with hearing loss in low and middle-income countries, and fewer than three in 10 in high-income countries, use hearing aids.
Untreated hearing loss is associated with greater cognitive decline and was estimated by the 2020 Lancet Commission on Dementia to contribute to around 8% of dementia cases worldwide -equivalent to 800,000 of the nearly 10 million new cases of dementia diagnosed every year.
There are a number of ways experts think untreated hearing loss may contribute to cognitive decline and dementia.
Hearing loss can make the brain work harder to the detriment of other mental functions like thinking and memory.
Another possibility is that hearing loss causes the ageing brain to shrink more quickly, and a third possibility is that it leads people to be less socially engaged and the reduced stimulation may result in brain atrophy.
The Achieve trial, published in The Lancet, included 977 adults aged 70–84 with untreated hearing loss who were free from substantial cognitive impairment in four communities across the US.
They were from two populations – older adults participating in a longstanding observational study who were at higher risk of cognitive decline (ARIC study), and a group of healthy volunteers.
It looks like even super-healthy people, which may include those recruited to ARIC 40 years before, eventually become people at risk of dementia— Gill Livingston
People were split into two groups, having either a hearing intervention (audiological counselling and hearing aids) or more generalised counselling on healthy ageing, and were followed up twice a year over three years.
On average, people from ARIC were more likely to be older, female, have more risk factors for cognitive decline, and have lower cognition scores at the start of the study than the volunteer group.
Both groups had similar hearing levels at the start of the study.
The study found that the hearing intervention did not reduce cognitive decline over time, with no significant difference in cognitive change between those receiving the hearing intervention and the health education over three years.
However, in the ARIC group, three-year cognitive change was 48% lower in the group given the hearing aids, compared with the other group.
Prof Lin said: “Despite similar levels of hearing at the start of the study, it’s likely that volunteers in the healthier cohort experienced slower rates of cognitive change than ARIC participants because they tended to be younger, had fewer risk factors for cognitive decline, and had better initial cognitive scores.
“This much slower rate of cognitive decline may have limited any effect of hearing aids in further reducing this decline over the relatively short three-year follow-up.”
Dr Charles Marshall, clinical senior lecturer at Queen Mary University of London, said: “These findings show us that there might be a small benefit of hearing aid use in reducing cognitive decline in an otherwise healthy population with hearing loss, but they don’t yet tell us whether hearing aids are actually preventing dementia or just improving people’s ability to perform cognitive testing.”
Gill Livingston, professor of psychiatry of older people at University College London, said: “Overall, the findings from this study are huge and hopeful results. Hearing aid treatment could really make a difference for populations at risk of dementia.
“These are for short-term dementia trials but interestingly, it looks like even super-healthy people, which may include those recruited to ARIC 40 years before, eventually become people at risk of dementia.
“Interventions to prevent dementia should recruit those at risk for timely results, but healthy people may develop risk over time.”
