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Chronic hearing loss linked to cognitive decline, depression

Chronic hearing loss may be linked to cognitive decline and late-life depression, and these associations may be explained by behavioral factors and/or neuropathologic mechanisms, according to a review published in The American Journal of Psychiatry.

The authors assessed various reviews and meta-analyses to identify studies linking peripheral age-related hearing impairment to cognitive decline in older adults. In the strongest of these studies, researchers followed 639 participants in the Baltimore Longitudinal Study of Aging with available audiometric testing data who had no dementia at baseline.

Over a 17-year follow-up, participants who subsequently developed dementia had significantly greater hearing loss per year vs. those without dementia. The researchers also identified data from the National Health and Nutritional Examination Study (NHANES) which showed an association between worsening hearing loss and decreased processing speed and executive function. In the Health Aging and Body Composition Study, participants with hearing impairment at baseline showed significantly higher rates of cognitive decline on the Modified Mini-Mental State Examination and Digit Symbol Substitution Test over 6 years. These studies suggested that central auditory processing dysfunction, as evaluated by dichotic listening tests, is strongly correlated with later dementia diagnosis.

The authors then evaluated associations between hearing loss and cognitive decline and depression. Behavioral analyses of these associations found that hearing loss frequently leads to impaired social functioning, with older adults often withdrawing from social circles and leaving their homes less frequently. Observational studies of older adults have reported that in both community and nursing home environments, individuals with hearing loss have 1.4 times greater likelihood of showing low social engagement, and 1.3 times greater odds of less frequent participation in social activities. In addition to its effects on social engagement, impaired hearing can also reveal or accelerate cognitive decline by reducing cognitive reserve. Depletion of cognitive reserve is associated with significantly increased risk of dementia.

The authors also reviewed and reported on the results of neuropathologic studies on these correlations.
They cited recent neuroimaging studies of age-related hearing loss, which have begun to characterize compensatory and neuroplastic changes linked to degraded auditory input that may represent pathways through which chronic hearing loss may lead to cognitive dysfunction and affective disorders. As hearing loss deteriorates over time, there is reduced input to the primary auditory cortex, which leads to secondary association cortices, and the auditory thalamus, which is seen in functional neuroimaging tasks as reduced activations to auditory stimuli. Diminished neural response to auditory input changes functional connectedness in the default mode network, leading to increased activity in the cognitive control network to aid effortful listening. The use of this compensatory activity may burden the network’s capacity, and lead to executive dysfunction, which is frequently seen in older patients with depression, and is predictive of suboptimal response to antidepressants as well as recurring illness.
authors noted the etiological complexity of late-life depression and cognitive decline, and limitations of current treatments for both.

“Identifying risk factors or pathophysiologic subtypes based on neurobiological and or behavioral data may facilitate the development of novel treatment approaches tailored to the underlying pathophysiology,” the researchers wrote. “For these reasons, in combination with the data reviewed above, age-related hearing loss merits further empirical attention as a causal and/or precipitating factor for the development of dementia and depression.” – by Jennifer Byrne

Disclosure: Dr. Golub reports travel expenses paid for by Cochlear when involving training events organized by the company. The other authors report no relevant financial disclosures.