Hearing loss may be a sign of dementia, according to new research.
But a hearing aid could help prevent cognitive decline and dementia by improving verbal communication and keeping the brain healthy, say experts.
The study found a small association between age-related hearing loss (ARHL) and increased risk for cognitive decline.
This includes executive function – which is the equivalent of a CEO of the brain – and episodic memory – autobiographical events such as times, places. Hearing loss was also linked to slower processing speed, cognitive impairment and dementia.
It is estimated two-thirds of the over 65s suffer hearing loss and previous studies have shown ARHL precedes the onset of dementia by five to 10 years.
Experts have suggested the lack of mental stimulation experienced by those who are hard of hearing may play a role in declined cognitive function.
An hearing aid could improve verbal communication and keep the brain healthy, say experts (stock image)
Currently there is no cure for dementia but new drugs can slow down its progression and the earlier it is spotted the more effective treatments are.
Key findings
A limited number of studies have examined ARHL and cognitive decline but results have been inconsistent.
So researchers from Trinity College Dublin carried out a systematic review of 36 studies involving 20,264 participants to examine the issue.
David Loughrey, a PhD candidate involved in the research, said: ‘In this meta-analysis, ARHL had significant associations with accelerated multi-domain cognitive decline, cognitive impairment, and dementia, thus supporting further consideration of ARHL as a risk factor for these outcomes.
‘The associations, although small, were comparable in size and significance with other more commonly researched risk factors using meta-analysis.’
He explained that ARHL has been associated with loss of brain volume in both the grey matter and white matter.
And as Alzheimer’s disease progresses, brain tissue shrinks. In the early stages, short-term memory begins to decline when the cells in the hippocampus degenerate.
The link is unclear
However, Mr Loughrey said the association between ARHL and cognitive decline ‘remains unclear’.
He said it could be because of decline in the vascular system – the arteries and veins that carry blood throughout the body, delivering oxygen and nutrients to the body tissues.
And he said ARHL is a sign of frailty syndrome, which has been causally linked to dementia. Frailty is associated with a greater risk for falls, disability, hospitalisation and death.
‘Other hypotheses suggest that the association may be mechanistic, for example, ARHL causing cognitive decline through impaired speech perception,’ he explained.
Changes can improve cognitive decline
Mr Loughrey said the findings could mean that interventions to improve hearing can help reduce cognitive decline.
‘Hearing loss is easily diagnosed and can be treated,’ he said. ‘Although associations were small, treatment may cumulatively benefit cognition.
‘In patients with ARHL, these domains may benefit from improved verbal communication through use of hearing aids.’
He said further studies exploring the cognitive benefits of hearing loss treatment are needed.
Research is also needed to know whether treatment, alone or as part of a wider approach, improves dementia outcomes.
Lack of mental stimulation
Dr Carol Routledge, director of research at Alzheimer’s Research UK said there may be a link between hearing loss and dementia, but the lack of mental stimulation experienced by those who are hard of hearing may also play a role.
She said: ‘This small but statistically robust association between hearing loss and a decline in memory skills adds to mounting evidence of a link, but the study does not conclusively show that hearing loss is driving memory problems.
‘Hearing loss is associated with dementia risk factors like heart disease, which could also be an underlying reason for the link observed in this study.
‘Some research suggests that being socially engaged and mentally active could help to boost cognitive reserve – a kind of mental resilience that may delay the effects of a disease like Alzheimer’s.
‘As things that we hear can provide mental stimulation and a means of social interaction, a loss of hearing could influence cognitive reserve, leaving people more vulnerable to memory and thinking decline.’
The study was published in the journal JAMA Otolaryngology – Head & Neck Surgery.