A Korean study has found that the impact of hearing loss on dementia depends on the severity of the hearing loss. The more severe the hearing loss, the greater risk of dementia, the study data showed. The study also found that the risk of dementia when having a severe hearing loss especially increases for people younger than 65 years of age.
In the study, there was a 1.3 times higher risk of getting dementia when having a severe or profound hearing loss compared to people with normal hearing. For those younger than 65 years with severe hearing loss, there was a 1.6 to 1.9 times higher the risk of dementia, depending on the severity of the hearing loss.
382,404 participants were included in the study which included 191,202 participants registered as people with a severe hearing loss and a matched pool of 191,202 participants with normal hearing.
Grades of severe hearing loss
In the study, severe hearing loss was categorised into three groups based on the severity.
According to the Korean National Disability Registry (NDR), the degree of severe-profound hearing loss was classified into six grades: 1st grade disabling HL (both-sides HL ≥ 90 dB HL and speech disorder), 2nd grade (both-sides HL ≥ 90 dB HL), 3rd grade (both-sides HL ≥ 80 dB HL), 4th grade (both-sides HL ≥ 70 dB HL), 5th grade (both-sides HL ≥ 60 dB HL). 6th grade of disabling hearing loss (ipsilateral hearing loss or severe asymmetrical hearing loss) was defined as those with worse-side hearing loss of 80 dB HL or more and other-side hearing loss of 40 dB HL or more.
Among those with hearing loss, 72,090 participants were classified with 1st grade to 3rd grade disabling hearing loss while 86,905 participants were classified with 4th and 5th grade disabling hearing loss. The number of participants with 6th grade disabling hearing loss was 32,207.
This study used nationwide data from the NHID, which is operated by the Korean National Health Insurance Service (KNHIS) and from the Korean National Disability Registry (NDR). Pure-tone thresholds were obtained using the pure-tone averages (PTAs) at four frequencies (0.5 kHz, 1 kHz 2 kHz and 4 kHz).
The study, “Association between the severity of hearing loss and the risk of dementia within the 2010–2017 national insurance service survey in South Korea”, was published in the journal Scientific Reports.
Sources: pubmed.ncbi.nlm.nih.gov and the Journal Scientific Reports