Hearing Loss and Cognitive Decline

Originally published on Health & Nature News

Hearing loss in the US is experienced by around 28 million adults over the age of 20 and, although in decline, the condition is strongly associated with sex, race and ethnicity, educational level, exposure to noise and increasing age.¹ Globally, hearing loss is the third leading contributor to years of life lived with disability and a major public health issue.² Cognitive decline includes a number of progressive factors related to deteriorating cognitive abilities, an individual’s ability to function independently and without support, and a reduction in social relationships. Understanding the underlying contributors to the incidence and progression of cognitive decline has the potential to enable the development of better diagnosis tools, as well as interventions and treatments which can successfully improve cognitive ability.

Several studies have demonstrated that hearing loss is associated with cognitive decline amongst those over the age of 65 – although whether hearing loss should be considered a marker of cognitive decline or a risk factor is, as yet, unclear.³ An association between the condition and processing via the psychomotor and executive functioning has been demonstrated.⁴ Furthermore, hearing loss has also been found to be associated with a range of other health outcomes including falls, depression and dementia.⁵ Because of such associations, untreated hearing loss substantially contributes to the healthcare costs of the older US population.⁶

The biological mechanisms underlying the associations between hearing loss and cognitive decline are not fully understood, but include declines in the following:

• Cortical processing – the tools engaged in cognitive behavior and responses.
• Cognitive load – the effort being used in working memory (temporary holding of information).
• Social isolation – caused by declines in auditory information to the cortex.
• Intellectual stimulation.
• Chronic inflammation caused by aging.³

These mechanisms have the potential to cause significant changes in the structure of the brain and its function.⁷ There is also some evidence that the loss of any of the senses, such as vision, could be considered a marker of potential cognitive decline.⁸

To reduce the impact of hearing loss upon cognitive decline, recent studies have demonstrated that auditory rehabilitation, through the use of cochlear implants and hearing aids,⁹ can be effective at reducing cognitive decline by improving both short-term and long-term memory tasks, levels of depression and improving cognitive status scores among older adults.^9,10 Among those who are profoundly deaf, cochlear implants have been found to improve cognitive function, which adds further credibility to the association between the two conditions.¹¹

Hearing Loss and Dementia

Dementia causes a substantial amount of disability among the older population and there are currently no treatments which successfully reduce the symptoms and consequences of the disease.¹² It is estimated that around 5 million adults are living with dementia in the US, with this figure predicted to triple by 2050.¹³ Several modifiable risk factors are associated with dementia. These include reduced social interaction and physical activity and type-2 diabetes mellitus.⁷ Financially, dementia is expensive to treat and is comparable to heart disease and cancer in terms of healthcare costs.³ When dementia in particular has been the focus of research seeking to explore the impact of hearing loss, the evidence suggests a strong association between the two conditions, particularly among the older population.⁷ When compared with those without hearing loss, those with increasing hearing impairment in later life have been found to experience an increased risk of developing dementia and faster development of the symptoms of the disease once diagnosed.¹⁴ A systematic review of the literature found 17 studies with homogeneous results all indicative of an association between hearing loss and dementia.¹⁵

In conclusion, there appears to be an association between hearing loss and cognitive decline, with untreated hearing loss being the most important factor, although it is not clear if hearing loss is a marker of cognitive decline or a risk factor.¹⁶ With this in mind, future research is required to better understand the associations between hearing loss and cognitive decline, as well as the mechanisms underlying such associations. Healthcare providers should also receive training to increase their knowledge related to the importance of good hearing and the regular monitoring of their patients in this regard. For individuals, it advisable for those over the age of 50 to undergo hearing tests regularly and, if diagnosed with hearing loss, to participate in rehabilitative interventions which eliminate or slow down hearing loss at the earliest opportunity.¹⁷

Author: Dr. Vanessa Gordon-Dseagu gained her Ph.D. from University College London in 2014 and subsequently moved from the UK to Washington, D.C. to take up a postdoc fellowship within the National Cancer Institute’s (NCI) Metabolic and Epidemiology Branch. Since leaving NCI she has been working as a freelance epidemiologist, research and policy consultant. She has written and published numerous peer-reviewed papers, as well as several white papers and blog posts, and presented her work at internationally-renowned conferences. Currently, her work focuses upon a diverse array of epidemiological, public health and policy issues – including pancreatic cancer survival rates, the provision of end of life care in different countries, hypertension and healthcare costs, and the use of mobile phone applications to support the work of health professionals.