Does Hearing Loss Cause Dementia – Hearing loss is an important risk factor for the development of dementia, particularly Alzheimer’s disease (AD). Hearing loss in middle age doubles the risk of developing dementia compared to any single factor. However, given this strong association between hearing loss and AD, the mechanisms responsible for this association remain unclear. Observational research data on hearing loss and cognitive impairment, as measured by standardized questionnaires, have shown a strong relationship between them. Similar findings have been made in animal studies, suggesting that causing hearing loss through prolonged exposure to loud noises or blockage of the ear canal can reduce cognitive performance. Interestingly, patients with age-related hearing loss have increased amounts of phosphorylated tau in the cerebrospinal fluid, but no correlation with amyloid-β has been established. In addition, hearing loss leads to social isolation, possibly leading to the development of dementia by reducing cognitive load and processing demands. Given this link between hearing loss and dementia, the question arises whether hearing rehabilitation can moderate the onset or progression of AD. Indeed, a growing body of research shows that those who use hearing aids for age-related hearing problems maintain better cognitive function over time than those who do not. These are encouraging findings because they suggest that hearing aids may be a cost-effective treatment for those with hearing loss, both before (those at high risk of AD) and after symptoms develop. The purpose of this review is to summarize current theories of hearing loss and cognitive decline, present key findings from animal studies, observational studies, and summarize gaps and limitations that need to be addressed in this topic. Thus, we suggest directions for future research to address the lack of randomized controlled trials in this field. This inattention is responsible for making a strong decision to use hearing intervention to prevent cognitive decline associated with hearing loss.
Dementia is a global burden, with a 2022 report estimating that 55 million people were living with a diagnosis of dementia in 2019 (Gautier et al., 2022). Future projections show that the prevalence of dementia will increase, reaching 140 million people by 2050 (Gauthier et al., 2022). New interventions are essential to slow this exponential growth, improve the management of those already diagnosed, or prevent those at risk of developing it.
Does Hearing Loss Cause Dementia
Logically, risk factors for cognitive impairment precede risk factors for dementia due to its clinical progression. It is important to note that age is an important risk factor – the natural aging process increases the risk of cognitive decline independent of dementia. In fact, aging itself is associated with a 70% increased incidence of dementia (Huang and Adlard, 2019). Furthermore, loneliness and social isolation are well established as factors that contribute to poor cognitive functioning and are associated with increased rates of decline (Cacioppo and Hockley, 2009; Dominguez et al., 2021). Furthermore, studies have shown that individuals classified as socially isolated have a 50% increased relative risk of developing dementia (Evans et al., 2018; Dominguez et al., 2021). Interestingly, a recent Lancet review (Livingston et al., 2020), which focuses on various risk factors for the development of dementia, emphasizes the importance of risk reduction, suggesting that modifying such risk factors can reduce the likelihood of dementia by 40% ( LaPlume et al., 2022). Among various risk factors, including brain damage, hypertension, depression and diabetes, the review highlighted hearing loss (HL) as a potential factor that, when excluded, reduced the risk of dementia by 8%. Mild, moderate, or severe HL, especially in middle age (defined as age 45–65), is associated with a 2-, 3-, and 5-fold increased risk of cognitive impairment and dementia, respectively (Lin et al., 2011; Livingston et al., 2011). , 2011). 2020). Furthermore, observational studies have shown that the severity of hearing impairment (HI) is associated with the risk of rapid cognitive decline (LaPlume et al., 2022), and one report even showed that the risk of dementia increased linearly with initial severity. HL. 1.27 for 10 dB loss) (Ford et al., 2018). However, there are still limitations regarding confounding factors that may affect the generalizability of these findings (Ford et al., 2018).
Can Hearing Aids Delay Time To Diagnosis Of Dementia, Depression, Or Falls In Older Adults?
In this review, we investigate HL as a risk factor for the development of cognitive impairment and dementia, with a focus on molecular mechanisms. Here, we summarize studies on the clinical manifestations of HL in dementia, proposed mechanisms of this association, and the role of interventions, including the use of hearing aids (HA), to reduce the impact of HL on the progression of cognitive decline. dementia. We emphasize the importance of continuing to understand the relationship between the proposed mechanisms and cognitive impairment with the potential goal of providing new effective interventions to reduce the risk of developing HL dementia.
Hearing loss currently affects 466 million people worldwide (World Health Organization, 2021). Individuals suffering from HL disability represent more than 5% of the world’s population (World Health Organization, 2021), and it is predicted that by 2050, approximately 1 in 10 people will need hearing rehabilitation. Causes of hearing loss include genetics, ear infections, cervical compression (blocked ear canal), ear or head trauma, loud/loud noise exposure (NHL), ototoxic medications, and more.
The mechanisms of HL associated with dementia mainly involve changes in sensorineural hearing involving cochlear dysfunction. It is commonly seen as age-related hearing loss (ARHL) or presbycusis, which affects approximately 40% of people over the age of 65 (Gates and Mills, 2005). Causes of HL, including presbycusis, hearing loss (NIHL), and ototoxicity, all lead to persistent HL and subsequently lead to limited management options (Lee and Banks, 2019).
ARHL is highly polygenic, with more than 100 genes known to underlie human non-syndromic hearing loss (Lewis et al., 2018; Van Camp and Smith, 2023), and of these many genes, each likely contributes a small amount to give results. in presumed inheritance. 36–70% (Nagtegaal, 2019). In most cases, genetic deafness indicates changes in the cochlea, the organ of the sense of hearing; for example, the OTOF gene encodes the protein otoferlin, which allows synaptic vesicles to bind to the plasma membrane at the ribbon synapse. Thus, a mutation in this gene can lead to a lack of exocytosis in inner hair cells, which interrupts auditory signal transmission and can lead to prelingual deafness (Vona et al., 2020). However, some types of genetic hearing loss may be associated with defects in the central auditory system. Genome-wide association studies (GWAS) targeting genes associated with ARHL, although showing some overlap, do not show strong concordance among themselves (Nagtegaal, 2019; Wells et al., 2019; Liu et al., 2021; Lewis et al., 2022). When examining the genetic link between hearing loss and AD, no GWAS has found a direct causal link between ARHL and AD. However, a recent study using data from the UK Biobank (Brenowitz et al., 2020) found that genetic risk for AD also affects speech hearing. Furthermore, in another report (Mitchell et al., 2020), individuals with a high polygenic risk score (PRS) were more likely to have hearing loss than those with a low PRS.
Medications That Cause Hearing Loss
Sudden-onset hearing loss (SSHL) has also been identified as a risk factor for the development of dementia. This form of HL is characterized as an otologic emergency, defined by HL of at least 30 dB over a 72-hour period affecting at least three different hearing frequencies, often with a viral, vascular, or autoimmune etiology (Lee and Banks , 2019). A retrospective cohort study comparing the incidence of dementia in individuals with a previous diagnosis of SSHL found that the occurrence of SSHL was associated with a 1.39-fold increased likelihood of developing all-cause dementia (Tai et al., 2021).
However, especially in presbycusis, various other mechanisms are also involved, including metabolic factors (e.g. mitochondrial dysfunction), oxidative stress (including changes in reactive oxygen species and superoxide dismutase deficiency), neurotransmitter imbalances (GABA deficiency) . others (Jafari et al., 2021) (Figure 1). Further understanding of the underlying mechanisms and how these different classes of ARHL can lead to dementia is not yet fully understood (Bowl and Dawson, 2019).
Figure 1. Different types of age-related hearing loss, including atrophy of the stria vascularis, loss of hair cells, and primary degeneration of cochlear neurons (Quaranta et al., 2015; Fortunato et al., 2016). Specific changes observed in stria vasculature include age-related morphological changes such as numerous cytoplasmic vacuoles, enlarged intracellular space, and disorganization of mitochondria and their components, especially cristae (Liu et al., 2020). These changes have been demonstrated by oxidative damage and downregulation of TMEM16A, a calcium-activated chloride channel (Spicer and Schulte, 2005; Zhou et al., 2019). Cochlear disease or injury has been shown to cause hair cell loss with potential causes including chronic exposure to industrial noise, reactive oxygen species, and superoxide dismutase (SOD1) deficiency (McFadden et al., 1999a,b, 2001; Emmerich et al. , 2000;
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