medwireNews: Hearing loss significantly increases the risk for Parkinson’s disease (PD) among US veterans, with hearing aids partially mitigating the risk, a study concludes.
After controlling for age, smoking history, and frailty, the risk for developing PD over 10 years of follow-up was 26% higher in people with any hearing loss than in those with normal hearing.
Moreover, receipt of a hearing aid within 2 years of audiogram-confirmed hearing loss was associated with 21.6 fewer incident cases of PD per 10,000 person–years at 10 years, compared with not receiving a hearing aid.
“Hearing screening and hearing intervention are low-cost, low-risk interventions that may influence later development of synucleinopathy,” Lee Neilson (University of Oregon Health Center, Portland, USA) and colleagues write in JAMA Neurology. They add that hearing loss “may be the most important modifiable risk factor for dementia in midlife and could prove to be the same for PD.”
The investigators analyzed electronic health data from 3,596,365 US military veterans, excluding those younger than 40 years old and those with pure conductive hearing loss. Participants were defined as having PD if they were 40 years and older, had one or more PD-related International Classification of Diseases (ICD)-9 or ICD-10 codes, had at least 5 years of ICD-coded medical records before the first PD ICD code, and had two PD medication prescriptions. The participants had a mean age of 67 years, 96% were men, and 86% were White.
A total of 20.8% of the participants had normal hearing (pure tone average threshold <20 dB) at the time of audiometry examination. Among the remaining 79.2% with hearing loss, 30.0%, 28.9%, 15.8%, and 4.3% had mild (20–<35 dB), moderate (35–<50 dB), moderate-to-severe (50–<65 dB), and severe-to-profound (65–120 dB) hearing loss, respectively. Hearing loss was linked to older age, higher scores on the Veterans Affairs Frailty Index, being a former smoker versus a current or never smoker, and hearing aid use at baseline.
Over a mean of 7.6 years of follow-up, PD incidence rates per 10,000 person–years were a respective 3.69, 8.77, 11.1, 11.3, and 11.6 for those with normal, mild, moderate, moderate-to-severe, and severe-to-profound hearing loss, while the mortality rate ranged from 103 to 1140 deaths per 10,000 person–years.
Neilson et al found that individuals with mild hearing loss had a similar PD incidence to those with normal hearing until 5 years of follow-up, after which the number of additional PD cases in this group increased to a significant 6.1 per 10,000 people at 10 years and 9.5 per 10,000 people at 20 years.
All other hearing loss groups showed a significantly higher incidence of PD than those with normal hearing at all time points except for those with severe-to-profound hearing loss in in the first year. The greatest effects were seen over the first 10 years, at which point the number of additional PD cases per 10,000 people versus those with normal hearing was a significant 15.8, 16.2, and 12.1 for those with moderate, moderate-to-severe, and severe-to-profound hearing loss, respectively. After 10 years, death as a competing risk factor had a greater effect.
The investigators observe that hearing loss synergized with prodromal PD disorders, such as constipation, depression, and anxiety, but not with traumatic brain injury or tinnitus.
“This is important because tinnitus may be overrepresented in a sample of military veterans, and it may influence sleep and mood symptoms known to be associated with PD,” they write.
Neilson and colleagues speculate that hearing loss could play a causal role in neurodegeneration, or act indirectly by limiting social engagement, or aggravating depression and general functional decline.
Receipt of a hearing aid versus not receiving one was associated with a significant 2.1 to 22.6 fewer PD cases per 10,000 person–years between 1 and 20 years of follow-up, the researchers note.
However, they add that it is possible 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.”
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