Over the past decade, a growing body of evidence has revealed that hearing loss is strongly associated with decreased functional brain tissue volume and cognitive decline. That leads many people to the question, can hearing loss shrink your brain?
Firstly, it is important to make it clear that no research to date shows that hearing loss leads to brain shrinkage and cognitive decline. In other words, cognitive impairment, including dementia and brain atrophy, is not demonstrably caused by hearing loss.
The human brain is a remarkable and highly complex organ, and researchers don’t yet understand if hearing loss leads to cognitive impairment and structural brain changes directly or through an indirect mechanism.
However, there is a significant correlation between hearing loss and cognitive impairment, and therefore unmanaged hearing loss may accelerate brain shrinkage.
Why is Brain Shrinkage Implicated in Hearing Loss?
Brain shrinkage or cerebral atrophy refers to a decline in the number of brain cells, called neurons, or a loss of connections between neurons. Brain atrophy may be limited to one area of your brain or affect the whole brain.
According to the National Institute of Neurological Disorders and Stroke (USA) cerebral atrophy is caused by normal aging, various diseases and disorders, infections and brain injuries. Included in the list of causes are Alzheimer’s disease and other forms of dementia.
In an analysis published in Laryngoscope Investigative Otolaryngology, researchers summarised the results of 17 reliable studies and found age-related hearing loss is associated with an increased risk of dementia, cognitive decline and cerebral atrophy.
With almost ten years of studies indicating a link between hearing loss and dementia, brain shrinkage is considered to be a significant correlating factor of these two disorders.
What Is Alzheimer’s and Dementia?
Although often used interchangeably, Alzheimer’s and dementia are not the same things. Dementia is not a single disease, it’s an overall term like heart disease. It covers a broad spectrum of distinct medical conditions, including Alzheimer’s disease. The Alzheimer’s Association (USA) estimates Alzheimer’s disease accounts for 60-80% of cases of dementia.
Dementia is identified by a progressive cognitive decline that impedes a person’s ability to live life independently. This impairment of mental faculty is bad enough to interfere with social and work skills. Memory, awareness of surroundings, learning ability, visual-spatial judgment, and higher executive functions such as mental flexibility, abstract thinking, and self-control may also be impaired.
The Alzheimer’s Society (UK) explains modern brain scan studies have found that an increased rate of brain shrinkage can be used to reliably and predictably diagnose future cognitive decline in patients. The most common types of dementia each start with shrinkage of brain tissue.
How Does Hearing Loss Cause Brain Shrinkage?
Hearing loss has not been proven to cause brain shrinkage. However, numerous studies have revealed a relationship between age-related hearing loss and structural brain changes exists.
Hearing loss is a type of sensory deprivation known as auditory deprivation. If the brain is deprived of sound for too long, as in the case of untreated hearing loss, the auditory cortex weakens, making hearing even more difficult.
Brain scans have shown the brain frequently has to work extra hard to compensate for hearing loss. This extra effort or cognitive load over taxes the brain, altering patterns of “normal” brain activity. When this happens, areas of the brain dedicated to higher-level thinking are “borrowed” for processing sound. Leaving them unavailable to do their original function.
With increasing listening effort, structural brain changes occur and cognitive decline and brain atrophy may set in much quicker than if the brain could process sounds normally. A compensatory brain reorganization could explain why age-related hearing loss is so strongly correlated with brain atrophy and dementia, and needs to be taken seriously.
Demonstrating a Link Between Hearing Loss and Brain Atrophy
Hearing Loss in Older Adults Affects Neural Systems Supporting Speech Comprehension, a 2011 study published in the Journal of Neuroscience demonstrated a significant linear relationship between hearing ability and brain tissue (gray matter) volume in the primary auditory cortex (the first relay station for auditory information in the brain).
The author’s also state they think it’s, “…plausible that changes in older adults’ peripheral hearing ability had a causal role in reducing gray matter volume in the auditory cortex.”
A 2014 study published in NeuroImage called Association of hearing impairment with brain volume changes in older adults found that individuals with hearing impairment compared to those with normal hearing had accelerated brain atrophy in the right temporal lobe.
Hearing Impairment Is Associated with Smaller Brain Volume in Aging published in Frontiers in Aging Neuroscience in 2016 studied the relationship between hearing impairment and brain volume in 2,908 participants with an average age of 65 years. The researchers found that people in the study with worse hearing were significantly associated with a smaller brain volume.
Anu Sharma, PhD, a researcher in the Department of Speech-Language and Hearing Science at the University of Colorado, studied how hearing loss alters the physical structure of the brain.
Sharma and her colleagues have shown when areas of the brain responsible for hearing receive degraded or decreased input due to hearing loss, parts of the brain which normally process sound may be “repurposed” by other intact and active brain functions.
“The hearing areas of the brain shrink in age-related hearing loss,” said Sharma. “Centers of the brain that are typically used for higher-level decision-making are then activated in just hearing sounds. These compensatory changes increase the overall load on the brains of aging adults. Compensatory brain reorganisation secondary to hearing loss may also be a factor in explaining recent reports in the literature that show age-related hearing loss is significantly correlated with dementia.”
What Can You Do To Help Prevent Hearing Loss and Brain Shrinkage?
Interestingly, studies have shown changes in brain structure may occur as soon as three months after the onset of hearing loss and could be reversible by a well-fitted hearing aid.
Simple interventions for conductive hearing loss such as earwax removal can also be highly effective.
If the association between hearing loss and cognitive decline is causal, it follows that rehabilitation for hearing loss has the potential to positively impact cognitive decline.
Hearing loss should not be dismissed as a normal part of aging and instead treated for structural changes in the brain.
What Can Be Done To Help Prevent Dementia Cognitive Decline?
According to Dementia prevention, intervention, and care: 2020 report of the Lancet Commission modifying 12 risk factors might prevent or delay up to 40% of dementias. Modifiable risk factors include:
- Education in early life
- Hearing loss
- Traumatic brain injury
- Alcohol misuse
- Later life:
- physical inactivity
- social isolation
- air pollution
The report recommends staying cognitively, physically, and socially active in midlife and later life. Using hearing aids is also specifically mentioned to reduce the risk posed from hearing loss. Regular exercise protects from dementia, perhaps by lowering obesity, diabetes, and cardiovascular risk.