The Relationship between Hearing Impairment and Dementia in Primary Care: A Nested Case-Control Study

Background: Dementia is a major cause of morbidity and mortality in older persons, and it has socio-economic impact on the society. Globally, it is the fifth leading cause of mortality, and the prevalence has been projected to triple by 2050. There is increasing evidence of a link between dementia and hearing loss, but the direction of cause and effect, and strength of association is unclear. Therefore, a nested case control study within one of the largest available databases of primary care records in the UK was used to check the association between hearing impairment and dementia. Aim: To estimate the proportion of exposure to hearing impairment in dementia cases and, to quantify the association by estimating the risk ratio. To establish whether the calculated risk ratio varies according to the timing of exposure from less than one month to over three years in cases compared to controls. Methods: A Nested Case-Control study was used to investigate the association between dementia, and hearing impairment and other closely related hearing problems by following-up 137,270 incident cases of dementia with 450,704 matched controls by age and gender who were 50 years and above in the UK primary care setting. Conditional logistic regression was used for the unadjusted risk ratio while multiple conditional logistic regression analysis was used to find an independent association between hearing impairment and dementia. Results: From the sample population, 25.7% of the cases and 23.9% of the controls were exposed to hearing impairment. There was a 10% (RR=1.10, 95% CI=1.08-1.12) increased risk of dementia after exposure to hearing impairment and this risk was greatest within four weeks of exposure (RR=1.68, 95% CI=1.52-1.85). However, the association was confounded by referral to ENT. Conclusion: This study shows that hearing impairment could precedes the development of dementia, and it could increase the risk of dementia by 10%, but this link is greatest within a month of exposure to hearing impairment. Consequently, hearing impairment could be an indicator to screen for before the development of dementia.