Hearing Loss Linked To Dementia

Recent findings from the Baltimore Longitudinal Study on Aging indicate that there is a possible relationship between hearing loss and dementia. However, it is unclear whether hearing loss may be an early sign of dementia or if it simply serves to increase one’s risk of cognitive decline. The study involved 639 cognitively healthy participants who were tested for hearing loss between 1990 and 1994, and then monitored for an average of 12 years. A total of 58 participants went on to develop dementia, with 37 developing Alzheimer’s. As the severity of baseline hearing loss increased, so did the risk of incident dementia. Specifically, for participants 60 and older, 36.4% of the risk of dementia was attributable to hearing loss. Beyond a hearing loss of 25 decibels, every additional loss of 10 decibels lead to an increased risk of Alzheimer’s by about 20 percent.

While the exact mechanisms underlying the link found in the current study are unclear, it is hoped that hearing may be able to serve as a biological marker of aging. It is possible that hearing loss might result from damage to nerve cells which may then serve as a marker for similar damage to neurons in other areas of the brain, such as those involved in memory. However, there is no exact cut-off point that separates those who will develop dementia from those who will not, so findings from this research can not currently be used for detection or screening. Other possible explanations for the observed relationship include that hearing loss may lead to an exhaustion of cognitive reserve, which could later present as dementia, or that it may lead to social isolation and a decrease in environmental enrichment; all of which have the potential to increase one’s risk for dementia.

Further research is needed before a clear link can be established between hearing loss and dementia. Along these lines, are two concurrent studies; the SMART study (Studying Multiple Outcomes after Aural Rehabilitative Treatment), which is looking at the effects of hearing aids and cochlear implants on the cognitive functioning of adults 50 and older. The second study, run by the National Institute of Aging, is researching the association between hearing loss and changes in MRI images of the brain. Both of these studies will lead to an advancement of the understanding of how hearing loss affects brain function, both in those with and without dementia.