Dissecting the Interactions of Diabetes Mellitus and Hearing Loss with Cognitive Decline and Dementia

Abstract

The aging population is increasingly affected by both diabetes mellitus and hearing loss, two conditions that often coexist and can significantly impact quality of life. As the prevalence of diabetes rises with age, so does the incidence of hearing impairment, with both conditions contributing to cognitive decline and functional limitations. The interplay between diabetes, hearing loss, and cognition highlights the need for comprehensive healthcare strategies that address the unique challenges faced by older adults. This review explores the mechanisms underlying the interplay between these three conditions, including mitochondrial dysfunction, neuroinflammation, oxidative stress, and microangiopathy.

Keywords: brain; cochlea; cognition; dementia; diabetes mellitus; hearing loss.

Figure 1

Potential mechanisms interlinking between diabetes mellitus, hearing loss, and cognitive decline. Many factors contribute to hearing loss and cognitive impairment. Mitochondrial dysfunction and oxidative stress contribute significantly to the pathophysiology of both hearing loss and dementia. Type 2 diabetes mellitus can cause hearing loss by microangiopathy, neuropathy, oxidative stress, and mitochondrial dysfunction, which can affect the cochlea and auditory pathways. Hearing loss can further impact dementia by central and peripheral mechanisms, as well as social isolation and depression. AGEs: advanced glycation end products. * Temporal lobes and other regions associated with auditory processing and cognitive [5,6]; ** neuroinflammation and tau protein phosphorylation in the hippocampus [7]. How cognitive decline could impact diabetes incidence is beyond the scope of this article.

Figure 2

Prevalence of diabetes, hearing loss, and dementia. Type 2 diabetes mellitus (T2DM) and age-related hearing loss are highly prevalent conditions, with an overlap ranging from 20% to 60% according to various cohort studies (Table 1). In contrast, dementia is less prevalent and shows approximately a 10% overlap with diabetes. The sizes of the circles represent population size. Data taken from WHO reports on diabetes, hearing loss, and dementia. These estimates are approximations, as the diagnostic criteria for hearing loss, the degrees of cognitive decline, and the stages of dementia vary considerably. This variability complicates the ability to define a precise overlap between hearing loss, dementia, and diabetes mellitus. Therefore, we present general trends rather than exact figures.