Hearing loss in older age appears to be an independent risk factor for later development of Parkinson’s disease but hearing aids appear to attenuate this risk, a large study suggests.
Researchers used data from a US veterans’ health study to compare hearing loss measured by audiograms with later diagnosis of Parkinson’s disease (PD).
They said the data showed “a strong association between hearing loss and PD” and the more severe hearing loss a person had in the study, the more likely they were to develop Parkinson’s.
But if a person with hearing loss received a hearing aid within two years of their audiogram, the risk was reduced, suggesting effective management of hearing loss could mitigate Parkinson’s risk.
Writing online in JAMA Neurology on 21 October 2024, researchers from Oregon Health and Science University said the risk of developing Parkinson’s after objective hearing loss had been unknown, Parkinson’s studies using self-reported hearing loss were insensitive and objective data was lacking.
They said prevalence of Parkinson’s was expected to grow and there was a lack of disease-modifying therapies.
“Identifying potentially modifiable prodromal symptoms, and ultimately intervening, could not only delay decline in quality of life but also substantially reduce the future economic burden of PD,” they wrote.
They undertook an electronic health record (EHR)–based cohort study using a national database of US military veterans at the Department of Veterans Affairs. This system was ideal because it offered comprehensive audiological evaluations with data linked to 20 years or more of EHR data, they added.
Veterans Affairs audiological services generated substantial audiometric records as the largest employer of audiologists in the US and offered hearing aids to veterans at no cost if medically appropriate.
It was also important to test the interaction with traumatic brain injury (TBI) because TBI changed the baseline risk of PD, and hearing loss may be a consequence of TBI, they added.
Nearly 3.6 million studied
“In this cohort study of electronic health record data for more than three million US veterans with a mean 7.6 years of follow-up, hearing loss was associated with incident PD in a dose-dependent manner, even after adjusting for competing risk of death, age, head trauma, frailty, and established prodromal disorders,” they said.
“This risk was attenuated by hearing aid dispensation.
“Our major finding is that hearing loss, as defined by objective audiograms, is associated with additional risk of developing PD later in life in a dose-dependent manner, such that worse hearing confers more risk. This risk difference is seen as early as one year after the initial audiogram, and differences widen dramatically over the next 10 years.”
Hearing loss of any severity was associated with an increased risk of PD at 10 years, with a hazard ratio of 1.26 compared with normal hearing.
Compared with normal hearing, there were 6.1 extra cases of incident Parkinson’s disease in people with mild hearing loss, 15.8 with moderate hearing loss, 16.2 with moderate-to-severe hearing loss, and 12.1 with severe-to-profound hearing loss at 10 years.
When hearing aids were dispensed within two years of an initial audiogram, incident Parkinson’s decreased by 21.6 cases at 10 years.
“While our data provide strong evidence that hearing aid administration reduces PD risk on a population level, the present methods did not allow us to assess hearing aid adherence or physical, cognitive, or other social factors influencing the prescription probability or decision to wear a hearing aid, which may be moderators of the expected benefit,” they said.
“In particular, the possibility remains that the individuals who receive hearing aids under current practice policy tend to be those most expected to benefit from them, and it is unknown whether this benefit would extend to any potential user if dispensation were expanded more broadly.”
Neurodegeneration theory
They suggested widespread screening for hearing loss and appropriate use of hearing aids may reduce Parkinson’s incidence.
“Hearing loss may represent early, extrastriatal pathology,” they wrote, adding that additional studies were needed to examine the mechanisms underlying the association between hearing loss and PD.
Further prospective studies assessing individual abilities to understand speech in the absence of pure tone identification were also warranted.
“While this study shows a strong association between hearing loss and PD, it does not elucidate a mechanism. One possibility is that hearing loss plays a causal role in neurodegeneration,” researchers said.
“There has been in vivo demonstration of greater tau neurofibrillary degeneration in cognitively unimpaired participants and greater neocortical Lewy bodies in cognitively impaired participants with clinician-reported hearing loss.
“This is further supported by other studies documenting elevated cerebrospinal fluid tau levels and accelerated global brain volume atrophy in individuals with hearing loss.”
The researchers suggested future work could build on their study to evaluate the relationship between hearing loss and α-synuclein burden or functional dopaminergic deficits, to determine if hearing impairment could be localised more precisely along the auditory neurophysiological circuit to clarify a unique PD phenotype, and to assess whether these were altered by hearing aid use.
A second possibility was that hearing loss acted indirectly by limiting social engagement or aggravating depression and general functional decline. Parkinson’s disease, and perhaps up-stream hearing loss, was associated with impaired speech and this may cause downstream suboptimal social interaction, a risk factor for PD and dementia, they hypothesised.
Thirdly, hearing loss might limit the neural resources needed for optimal performance through increasing cognitive load, and treating this may mitigate PD risk, they said.
The researchers were Dr Lee Neilson, a neurologist specialising in Parkinson’s disease from Oregon Health and Science University (OHSU), audiologist, hearing scientist and epidemiologist Dr Kelly Reavis from the National Center for Rehabilitative Auditory Research and OHSU, statistician Mr Jack Wiedrick from OHSU, and Dr Gregory Scott from OHSU Department of Pathology.
