32% of dementia cases could be linked to hearing loss

• Hearing loss is common worldwide, and the incidence increases with age — around one-third of those aged over 60 have some hearing loss.

• Studies have linked hearing loss to an increased risk of developing dementia.

• Now, a study in older adults has found that, at a population level, hearing loss may increase dementia risk by almost one-third.

• The researchers suggest that treating hearing loss could delay, or even prevent, dementia for a large number of older adults.

According to the National Institutes on Deafness and Other Communication Disorders, around 15% of Americans aged over 18 report some problems with hearing. For 22% of those aged 65–74, and 55% of over-75s, hearing loss is disabling.

Studies have suggested that hearing loss may increase a person’s risk of cognitive decline, cognitive impairment and dementia. And there is some evidence that, for people at higher risk of cognitive decline, hearing aids could reduce that risk.

A new study, led by researchers from Johns Hopkins Bloomberg School of Public Health, has found that moderate hearing loss may increase the risk of dementia by around 17%, and mild hearing loss by 16%.

The research is published in JAMA Otolaryngology – Head & Neck Surgery.

Corresponding author Jason R. Smith, ScM, doctoral researcher at the Johns Hopkins Bloomberg School of Public Health, told Medical News Today: “I think what our current study adds is that more dementia in the population could be associated with hearing loss than previously thought, in part because of how widespread hearing loss is in older adults.”

“Although we assume here that hearing loss is causally related to dementia, which is a very strong assumption given no definitive randomized trial evidence to date to support it, it could be that treating hearing loss might delay or prevent a large fraction of dementia at the population level,” he added.

Higher dementia rates in those with hearing loss

The prospective cohort study was part of the Atherosclerosis Risk in Communities Neurocognitive Study (ARIC-NCS). Community-dwelling older adults from four centers — Jackson, MS, Forsyth County, NC, the Minneapolis suburbs, MN, and Washington County, MD — were included.

All were aged between 66 and 90 years (mean age 74.9 years) without dementia at the start of the study. At their 6th visit to their study center, they underwent a hearing assessment. Researchers followed them up for up to 8 years, and recorded any cases of dementia.

The researchers analyzed the data to calculate the population attributable fraction (PAF) — an epidemiologic measure used to assess the public health impact of exposures in populations — of dementia associated with hearing loss.

They also investigated whether there were any differences by age, sex, self-reported race, or method of hearing loss measurement.

Audiometric testing found that almost two-thirds of the 2,946 older adults in the study had clinically significant hearing loss. Of these, 1,151 (39%) had mild hearing loss, 796 (27%) had moderate or greater hearing loss, and 1,097 self-reported some hearing impairment.

More than half of those with moderate or greater hearing loss used hearing aids. Few people with milder hearing loss used them.

Overall, any degree of audiometric hearing loss was associated with a 32% population-level dementia risk. However, the researchers found no association for self-reported hearing loss. The link between audiometric hearing loss and dementia was greater for those who were women, aged over 75, and white.

Why is there a link between hearing loss and dementia?

Research suggests that people with hearing loss may have changes in brain regions associated with attention and executive function in the frontal cortex, as well as the auditory regions of the temporal lobe. These parts of the brain are related to dementia symptoms.

However, Steven Allder, MD, consultant neurologist at Re:Cognition Health, suggested a simpler explanation for the relationship:

“When hearing is impaired,” Allder added, “the brain may divert resources to compensate for lost auditory information, leaving fewer resources available for memory and other cognitive functions. The resulting strain on cognitive reserves can accelerate decline in older adults.”

Diagnosing, treating hearing loss could lower dementia risk

“The study provides compelling evidence that objective hearing assessments are essential. Routine hearing tests should ideally commence in midlife, around 60 years old, to detect clinically significant changes early,“ said Allder.

“Early intervention could help mitigate the risk of dementia, particularly as misclassification of hearing loss rises sharply after age 70,” he further noted.

The study authors suggest that addressing hearing loss in later life could be an effective way to prevent or delay dementia.

Smith told us that it was still not known whether treating hearing loss reduces an individual’s risk of dementia. He highlighted results of the ACHIEVE trial, a large randomized controlled trial of older adults with hearing loss, which found that hearing aids made a difference only in older adults at high risk of cognitive decline.

However, he added that: “There are known benefits for improving communication and quality of life from treating hearing loss. So I would still encourage older adults to raise concerns about their hearing with their healthcare provider — early detection and management of hearing loss could have large benefits to their wellbeing.”

He stressed that hearing loss should not be viewed in isolation.

“It’s important to consider our sensory health collectively. For example, hearing impairment and vision impairment frequently occur together in older adults. Our future work aims to estimate the impact of multiple sensory impairments on dementia at the population level to inform dementia prevention strategies,” said Smith.

View the original article on Medical News Today