ST. PAUL, Minn., April 17 (UPI) -- The authors of a detailed analysis of thousands of medical records across four U.S. communities said Thursday they've found further evidence of a strong link between hearing loss and the onset of dementia in older adults.
Previous research has determined that seniors with more severe hearing loss also are more likely to have dementia, and that the likelihood of dementia is lower among hearing aid users compared to non-users, although no causal relationship has yet been proven.
Now, the first-ever study of the connection, involving large populations of thousands of patients across the country, has further reinforced the connection and is highlighting the importance of continuing to battle hearing loss among the seniors, according to researchers from Johns Hopkins University, New York University and elsewhere.
The new study, published in JAMA Otolaryngology-Head & Neck Surgery, examined the medical records of nearly 3,000 people participating in the long-term ARIC, or Atherosclerosis Risk in Communities, study, which began 38 years ago and is ongoing.
That landmark effort, led by the National Institutes of Health, mainly seeks to understand the causes of atherosclerosis and heart disease. From 1987 to 2014, it tracked the health outcomes of 400,000 adults ages 35 to 84 living in four U.S. communities -- Forsyth County, N.C., Jackson, Miss., suburban Minneapolis and Washington County, Md.
By studying the records of 2,946 participants with a mean age of 75 years who were objectively assessed to have hearing loss, including up to eight years' worth of follow-up information, the authors of the news study estimated that nearly one in three new dementia cases among that population could be "attributed to clinically significant hearing loss."
The upshot of the findings is that "interventions for sensory health in late life might be associated with a broad benefit for cognitive health," they concluded, also urging that seniors' hearing be objectively measured by providers in subsequent research rather than accepting the "self-reporting" of patients, who tend to underestimate their own hearing loss.
One of the lead authors, doctoral student Jason R. Smith, of the Johns Hopkins Bloomberg School of Public Health in Baltimore, told UPI the analysis has broken new ground on several levels.
"To our knowledge, this is the first population-based study of this size and duration -- up to eight years -- to estimate how much dementia at the population level can potentially be linked to age-related hearing loss," he said in emailed comments.
"It's important that we also used an objective measure of hearing loss -- previous research tended to use 'self-report,' which is known to underestimate the occurrence of hearing loss in older adults."
This new study has strengthened the evidence for a hearing loss-dementia link in another way.
The population whose records were analyzed participated in both the ARIC study and another that was focused more closely on the connection: the 2023 Aging and Cognitive Health Evaluation in Elders, or ACHIEVE, study. That effort showed hearing intervention slowed down the loss of thinking and memory abilities among high-risk older adults by 48% over a three-year span.
"The population of older adults in our study is the same sub-group of older adults in the randomized ACHIEVE trial that derived benefit from a hearing intervention on reducing cognitive decline," Smith said. "This gives us more confidence that what we're estimating is applicable to the populations we would intend to target for interventions."
While the association between hearing loss and dementia is strengthening, it remains a mystery as to why they seem to be linked. There are a few potential explanations for the connection, Smith said.
"It could be that hearing loss increases social isolation -- and decreases cognitively enriching activities," he noted.
"Hearing loss could also increase the 'strain' on one's brain -- [for example], think of the strain from having persistent difficulty with hearing while simultaneously attempting to do tasks of daily living. Or, hearing loss could directly affect the function or structure of the brain."
Conversely, there may not be a "mechanistic" explanation at all, but rather an as-yet unknown common cause of both hearing loss and dementia. Perhaps vascular risk factors such as diabetes, or even just age, are at the root of both, meaning the associations would not actually be causal.
"Unfortunately, high quality randomized trials that would give us more confidence in a causal association are limited," Smith said. "Only one randomized trial [ACHIEVE] to date has investigated whether a hearing intervention reduces the rate of cognitive decline, and the interpretation of those findings is challenging."
