Hearing Loss and Dementia in Old Age

Dementia is a general term for a category of acquired, persistent intellectual impairments, encompassing Alzheimer's disease (also known as senile dementia), vascular dementia, dementia with Lewy bodies, Parkinson's disease dementia, frontotemporal lobar degeneration, as well as dementia caused by other central nervous system disorders or systemic, metabolic, and toxic conditions. Among these, Alzheimer's disease accounts for the highest proportion, approximately 50-70%. Dementia predominantly affects older adults and shows a strong age-related trend. Statistics indicate that for every five-year increase in age, the prevalence of dementia increases by a factor of 0.74. According to current disease classification, older adults over the age of 65 diagnosed with dementia are considered to have "dementia in old age."

With the progression of population aging, hearing loss in older adults frequently co-occurs with dementia. Some studies currently suggest that hearing loss is a risk factor for the development of dementia in old age, while others propose that hearing loss may be a prodromal symptom. The two conditions may interact and influence each other bidirectionally.

Numerous existing studies have demonstrated a positive correlation between hearing loss and both cognitive decline and dementia. Some research has further identified that a subset of dementia cases are causally attributable to hearing loss, and this association appears to be independent of the specific type of dementia.

The currently accepted possible mechanisms linking hearing loss and dementia in old age include brain structural changes, social isolation, and cognitive load.

I. Brain Structural Changes

Since both dementia and hearing loss are age-related conditions, factors associated with aging—such as metabolic changes, neurodegeneration, and microcirculatory impairment—may simultaneously damage both the brain and peripheral nerves. Research has found that individuals with hearing loss exhibit accelerated atrophy of global and temporal lobe gray matter volume, with the right hemisphere showing greater involvement than the left. These regions are not only important for spoken language processing but are also involved in semantic memory during the early stages of mild cognitive impairment or Alzheimer's disease. Some studies with controversial findings suggest that hearing loss caused by cochlear microvascular pathology may simultaneously affect cerebral blood supply and nutrition, thereby impacting brain function and contributing to the pathogenesis of dementia. [1]

II. Social Isolation

This is the most readily understood mechanism from the perspective of general knowledge. Due to hearing loss, older adults may be unable to communicate normally with those around them, and consequently cannot receive timely and accurate environmental information feedback. The lack of linguistic and emotional stimulation directly affects brain structure and function, leading to a vicious cycle of "less and less communication," which in turn results in social dysfunction and social withdrawal, further exerting a negative impact on brain structure and function.

III. Cognitive Load

For individuals with hearing loss, sensory input to the central nervous system is reduced. When attempting to understand something, they may need to recruit additional cognitive functions to compensate, thereby increasing cognitive load and leading to an elevated risk of brain structural damage, which in turn heightens the risk of dementia.

In 2020, the renowned journal The Lancet published a report on the prevention, intervention, and care of dementia. After comprehensively analyzing multiple studies, the report identified twelve risk factors for dementia: low educational attainment early in life; hearing loss, traumatic brain injury (TBI), hypertension, excessive alcohol consumption, and obesity in midlife; and smoking, depression, social isolation, physical inactivity, air pollution, and diabetes in later life. [2]

According to the model presented by the Lancet Commission, hearing loss is an independent risk factor that can contribute to dementia as early as midlife. If detected and addressed promptly, the overall risk of developing dementia over the entire lifespan could be reduced by 8%.

Synthesizing the current body of research, we cannot conclude with certainty that a causal relationship exists between hearing loss and dementia in old age. However, it can be said that timely correction of hearing loss can effectively reduce the risk of developing dementia in old age. Given the complex etiology of age-related diseases, which are closely related not only to individual factors but also to family and societal contexts, prompt detection of disease and appropriate intervention can not only prevent potential complications but also play a significant role in supporting the mental health of older adults.

[1] Julie Hugo 1, Mary Ganguli. Dementia and cognitive impairment: epidemiology, diagnosis, and treatment. Pubmed. 10.1016/j.cger.2014.04.001.

https://pubmed.ncbi.nlm.nih.gov/25037289

[2] Prof Gill Livingston, MD, Jonathan Huntley, PhD, et al. Dementia prevention, intervention, and care: 2020 report of the Lancet Commission. The Lancet Journal. Volume 396, Issue 10248p413-446August 08, 2020.

https://www.thelancet.com/journals/lancet/article/PIIS0140-6736(20)30367-6/fulltext