Individuals who used hearing aids and cochlear implants for hearing loss had a decreased risk of cognitive decline, according to a new meta-analysis published online in JAMA Neurology.

The researchers found that using these hearing devices was associated with a 19 percent reduction in the risks for long-term cognitive decline and significantly associated with a three percent improvement in test scores assessing general cognition in the short-term.

“Hearing loss is recognized as the largest modifiable risk factor for dementia, responsible for 8 percent of dementia cases,” the study’s corresponding author, Benjamin Kye Jyn Tan, MBBS, dean’s fellow at the National University of Singapore’s Yong Loo Lin School of Medicine, told Neurology Today.

“However, it remained unclear before our study if treating hearing loss could potentially prevent dementia,” Dr. Tan added. “Dementia still has no cure after years of research, and prevention is our best weapon.”

The meta-analysis by Dr. Tan and his collaborators included randomized clinical trials and observational studies in peer-reviewed journals on the effect of hearing interventions on cognitive function, cognitive decline, cognitive impairment, and dementia in patients with hearing loss.

Other studies have indicated that hearing aids may prevent incident cognitive impairment by correcting hearing loss. Some observational studies have implied that hearing aids may lessen the onset of dementia, perhaps by decreasing cognitive load or resolving sensory deprivation in those with hearing loss. Yet not all observational studies demonstrated benefits from hearing aid use, “which may be attributed to a lack of consistency in wearing hearing devices in social situations or late implementation of these devices,” the authors wrote.

They noted that, “to date, no meta-analysis has pooled the available evidence on the cognitive benefit of hearing restorative devices. Because some studies may have an inadequate sample size, a pooled analysis may help increase the statistical power.” Their study, therefore, aimed “to analyze both cognitive scores and longitudinal data to determine the long-term associations of hearing restorative devices with cognitive impairment and incident dementia.”

The strengths of this meta-analysis include a rigorous systematic search and a large number of studies from around the world, making the findings more generalizable, Dr. Tan told Neurology Today. However, “we were unable to determine, based on the available data, if the severity of hearing loss affects the potential cognitive benefit to be gained by using hearing aids,” he said, citing this as a limitation of the study.

It was nonetheless encouraging that even patients who started with mild cognitive impairment in the pooled analysis also benefited from the use of hearing aids, as they also had an approximately 20 percent lower risk of progressing to dementia.

“This means that it is never too late to start using hearing aids,” he said, “and early treatment may help to preserve the most cognition, especially as it may become more difficult for the individual to accept hearing aids as dementia progresses.”

Dr. Tan and his colleagues recommended that clinicians consider conducing a hearing evaluation—which is simple, quick, harmless, and inexpensive—for every new patient with early dementia and as part of a routine health check for older adults.

“All neurologists, geriatricians, psychiatrists, otolaryngologists, and family physicians should strongly recommend their patients with hearing loss to use hearing aids or cochlear implants,” he said.

Methodology and Results

The analysis included studies (through July 23, 2021) from the PubMed, Embase, and Cochrane databases that focused on the effect of hearing interventions on cognitive decline and dementia in patients with hearing loss.

The review screened a total of 3,243 studies, including 31 studies (25 observational studies and six trials) with 137,484 participants, of which 19 studies (15 observational studies and four trials) were included in the quantitative analyses.

In the meta-analysis of eight studies, which involved 126,903 total participants, the follow-up spanned from two to 25 years. It assessed long-term associations between hearing aid use and cognitive decline and demonstrated significantly lower hazards of any cognitive decline among hearing aid users compared with participants with uncorrected hearing loss (HR, 0.81).

Another meta-analysis of 11 studies with 568 total participants that examined the association between hearing restoration and short-term cognitive test score changes showed a 3 percent improvement in short-term cognitive test scores after the use of hearing aids (ratio of means, 1.03).

Expert Commentary

An accompanying editorial in JAMA Neurology said the meta-analysis underscores that abundant evidence supports the association between hearing loss and cognitive decline/dementia.

While researchers await the results from randomized clinical trials, the authors of the editorial recommended that “physicians consider hearing evaluation as part of a standard dementia workup.”

Justin S. Golub, MD, MS, the editorial’s corresponding author, noted that hearing loss was recently recognized of one of the greatest potentially modifiable risk factors for dementia.

This study is one of the highest-quality reviews examining the relationship between hearing interventions and preventing cognition/dementia symptoms, said Dr. Golub, associate professor of otology, neurotology, and skull base surgery in the department of otolaryngology—head and neck surgery at Columbia University Vagelos College of Physicians and Surgeons and New York-Presbyterian/Columbia University Irving Medical Center.

Dr. Golub noted that a meta-analysis is more powerful than any single investigation and that the studies included were from multiple geographic regions around the world. The studies also adjusted for confounding variables, he said.

“The field is at a crossroads where randomized controlled trials are needed,” he said, pointing out that the study did not include any high-quality randomized controlled trials. Only such trials can establish a definitive causal association between hearing loss and cognitive decline/dementia.

Dr. Golub noted that hearing loss is largely ignored among health care providers other than otolaryngologists and audiologists. Unlike many other medical treatments, hearing aids pose almost no risk, he said.

“The study will hopefully encourage people to use these wonderful and now more affordable devices,” Dr. Golub said, noting that over-the-counter hearing aids became available in the fall.

Hearing restoration technologies (hearing aids and cochlear implants) should be recommended for patients with bilateral hearing loss even if the problem is significantly worse in one ear compared to the other, said Terry D. Fife, MD, FAAN, FANS, director of oto-neurology and balance disorders and director of graduate medical education at Barrow Neurological Institute in Phoenix, AZ.

“The findings of this study support the notion that hearing aids or cochlear implants may provide more than just the enjoyment of improved hearing,” he said, adding that these devices “may also provide additional benefits for the preservation of cognitive health.”

However, “hearing aids are often not covered by insurance because they’re not considered essential medical devices and are viewed as something of a luxury,” said Dr. Fife, who is also professor of neurology at the University of Arizona College of Medicine–Phoenix.

Dr. Fife explained that “hearing from both ears is fused in the brain to become a unified perception, which matters for quality of life, engagement in social interactions, and, in turn, delay or reduction in cognitive function.”

He added that binaural hearing improves speech comprehension. Sounds that are hardly heard with one ear at 10 feet can be heard much better by both ears up to 40 feet away. Localization of the direction of sound origin also improves with bilateral hearing, and auditory “deprivation” is lessened, with hearing being less difficult and better in situations with background noise.

“The brain is wired for hearing from both ears, which enhances social interaction and cognitive stimulation,” Dr. Fife said. “Studies suggest that hearing impairment is associated with cognitive impairment and improvement in hearing staves off the effects of cognitive decline in patients with functionally significant hearing loss.”

Dr. Fife noted that that the current meta-analysis had some limitations. “The definitions of hearing loss severity and clear educational levels were limited,” he said, and “there was not enough data to understand how much hearing loss matters and whether those without cognitive impairment at baseline lose ground without augmentation of hearing quality.”

The major point missing in these published papers was that the treatment for hearing loss stems from returning an audible signal across input levels and frequencies, said Catherine V. Palmer, PhD, professor and interim chair of communication science and disorders and professor of otolaryngology at the University of Pittsburgh.

This occurs when an audiologist measures a hearing aid’s output in a user’s ear and tunes the device based on the individual’s measured hearing and ear canal characteristics, which impact the amount of sound delivered to the ear, she said. “By just focusing on ‘devices,’ the authors imply that any device will return audibility, which is not the case.”

Dr. Palmer, who also is director of audiology at University of Pittsburgh Medical Center, said “it will be essential to control how the amplification is fit in order to reach any conclusion about the impact of treatment. So, future studies need to account for the hearing aid fitting and resulting audibility in order to actually assess the treatment on cognition. Just knowing that someone had an amplifier is not adequate to interpret a study.”

Still, Dr. Palmer said, “these findings of the meta-analysis provide a compelling argument for the referral of patients with concerns of cognitive decline for audiological assessment and treatment, given that treatment decreased the hazard of long-term cognitive decline.”

Article originally appeared on NeurologyToday