There is a surely a link between deafness and dementia but scientists cannot say that deafness causes dementia. How the connection between the two works is conjectural. But several scientific studies by Dr. Frank Lin of Johns Hopkins University show a definite link.
According to Dr. Lin and his researchers, the nature of the link is that people with hearing loss develop cognitive impairment earlier than people who hear well. The researchers found that the link is so strong that a person suffering from severe hearing loss is five times more likely to develop dementia over time than someone with average hearing. This is cause for concern, Lin and his colleagues wrote, because almost 70% of persons over the age of 70 have a degree of hearing loss.
The association between deafness and dementia is robust. The researchers ruled out all other possible factors associated with dementia risk, such as diabetes and high blood pressure. Lin and his colleagues found that people with hearing loss who did not have cognitive impairment at the start developed dementia at a 30% to 40% faster rate than people with normal hearing when tested over a six-year period.
The scientists are unsure how the link works. They theorize that the reason why deafness leads to dementia may be brain overload. With hearing loss, the brain must work overtime to process sound. This strains other cognitive functions like memory. Brain MRIs show the brain "borrows" from other regions to overcome the effect of hearing loss. Another theory is that deafness tends to isolate people socially. Social isolation is itself linked to the development of dementia.
The scientists are also unsure if earlier detection and treatment of deafness postpones cognitive decline. Tests are being designed to discover the effect optimal hearing treatments have on staving off dementia.
The researchers stated they must consider the possibility that the close association between hearing loss and dementia may be due to the fact that hearing loss impedes verbal communication and understanding. Thus, it is possible that deafness causes cognitively sound persons to do poorly on cognitive tests. It is also possible hearing loss was over-diagnosed with people with cognitive impairment. In other words, tests for cognitive impairment and hearing loss may tend to ascribe one loss to the other cause. However, the researchers do not believe either hearing or cognitive tests were compromised in the clinical setting. The scientists also considered the possibility that the same neurobiological processes may cause hearing loss and dementia, making them appear to be linked. But this was ruled out.
Although scientists have not proven that addressing hearing loss early and aggressively prevents the development of dementia, it is important for caregivers to notice and treat hearing loss early. This may help an elderly person to stave off dementia because the link is clear.
Lin and colleagues used data from the Baltimore Longitudinal Study on Aging (BLSA). The subjects were 639 people whose hearing and cognitive abilities were tested between 1990 and 1994. None of the subjects had dementia at the beginning of the study, although about 25% had hearing loss.
Closely examined on an annual or two-year basis, up to 2008, 58 of the 639 persons developed symptoms of dementia. Of the 58 persons, those with hearing loss had a double, triple and quintuple risk of developing dementia, if their hearing loss was mild, moderate or severe. The more serious their hearing loss, the more prevalent dementia developed. Treating deafness is a logical way to prevent cognitive decline.
Johns Hopkins University. (February 14, 2011). Hearing Loss and Dementia Linked in Study. News. Available online at http://www.hopkinsmedicine.org/news/media/releases/hearing_loss_and_dementia_linked_in_study Accessed March 17, 2017.
Johnson, M. (March 4, 2017). Family suspects dementia/deafness link. New Zealand Herald. Available online at: http://m.nzherald.co.nz/lifestyle/news/article.cfm?c_id=6&objectid=11810669 Accessed March 16, 2017.
Lin, F. R., Yaffe, K., Xia, J., Xue, Q-L., Harris, T.B., Purchase-Helzner, et al. (February 25, 2013). Hearing Loss and Cognitive Decline in Older Adults. JAMA Internal Medicine, 173(4):293-299. Doi:10.1001/jamainternmed.2013.1868, Available online at
Lin, F.R., Metter, E., O'Brien, R. J., Resnick, S. M., Zonderman, A. B., Ferrucci, L. (February 2011). Hearing Loss and Incident Dementia. Archives of Neurology, 68(2):214-220. Doi:10.1001/archneurol.2010.362. Available online at
http://jamanetwork.com/journals/jamaneurology/fullarticle/802291?version=meter%20at%20null&module=meter-Links&pgtype=article&contentId=&mediaId=&referrer=&priority=true&action=click&contentCollection=meter-links-click Accessed March 16, 2017.