Data from the Baltimore Longitudinal Study on Aging, begun in 1958, has revealed that seniors with hearing loss are significantly more likely to develop dementia than those who retain their hearing. The study involved 639 people whose hearing and cognitive abilities were tested between 1990 and 1994, then re-tested every one to two years. By 2008, 58 (9%) of them had developed dementia (37 of which were Alzheimer’s).
Those with hearing loss at the beginning of the study were significantly more likely to have developed dementia. The degree of hearing loss also correlated with greater risk: those with mild, moderate, and severe hearing loss had twofold, threefold, and fivefold, respectively, the risk of developing dementia over time. The association was maintained after other risk factors, (high blood pressure, smoking, education, age, sex, race) were taken into account.
The reason for the association is not yet known. It’s possible that a common pathology may underlie both, or that the strain of decoding sounds over the years may make the brain more vulnerable to dementia, or that hearing loss makes people more socially isolated (a known risk factor for dementia).
The findings do suggest that hearing loss should be regarded more seriously, and not simply accepted as a natural part of growing old.
 . Hearing Loss and Incident Dementia. Arch Neurol [Internet]. 2011 ;68(2):214 - 220. Available from: http://archneur.ama-assn.org/cgi/content/abstract/68/2/214