Association between the severity of hearing loss and the risk of dementia within the 2010-2017 national insurance service survey in South Korea.

Hearing loss and dementia are highly prevalent neurologic conditions in older adults that can considerably impact the quality of life and create social and familial burdens. To investigate the impact of hearing loss on the risk of developing dementia in a nationwide long-term follow-up study using data obtained from the South Korean National Health Information Database. Retrospective medical data for patients of all ages were extracted from the database between January 2010 and December 2017. According to the national disability registry, the degree of severe-profound hearing loss is classified into six grades. We categorized hearing loss into three groups based on the disability registry severity: (1) severe hearing disability (HD), defined as 1st to 3rd grade disabling hearing loss; (2) non-severe HD, 4th and 5th grade disabling hearing loss; and (3) ipsilateral HD, 6th grade disabling hearing loss. After adjusting for potential confounding variables, the hazard ratio (HR) for all dementia types was 1.336 (95% CI 1.306-1.367) in the severe HD group, 1.312 (95% CI 1.286-1.338) in the non-severe HD group, and 1.257 (95% CI 1.217-1.299) in the ipsilateral HD group. On assessing by the age group, the risk of all dementia types in patients younger than 65 years was as follows: HR 1.933 (95% CI 1.779-2.101), 1.880 (95% CI 1.732-2.041), and 1.601 (95% CI 1.435-1.787) in the severe, non-severe, and ipsilateral HD groups, respectively. This study demonstrates that the impact of hearing loss on dementia incidence is severity-dependent, and the risk increases in patients younger than 65 years of age.