Gustatory dysfunction and oral frailty: Emerging implications for Alzheimer's disease

Emerging evidence suggested that impairments in sensory function (e.g., vision, hearing, taste, smell, touch, and somatosensation) may be linked to the increased risk of late-life cognitive disorders, dementia, and Alzheimer's disease (AD). Among sensory changes, age-related gustatory function plays a critical role in appetite regulation and nutritional status, altering dietary patterns and leading to inadequate nutrient intake and an increased frailty risk, particularly oral frailty. This novel frailty phenotype showed an abnormal oral structure and/or decline in multi-faceted oral function and coexisting decline in physical and cognitive functions. In the present review article, we discussed the intricate interplay among gustatory dysfunction, oral frailty, and AD, addressing also possible underlying mechanisms. In AD, gustatory dysfunction was differentially associated with the severity of cognitive deficits. In AD patients, worse threshold scores and overall taste identification (particularly for sour) were found compared to controls, along with worse overall scores, sweet, and sour scores compared to subjects with mild cognitive impairment. Periodontal disease and number of teeth (two key indicators of oral frailty) were consistently associated with late-life cognitive impairment/decline and dementia, particularly AD. Although the mechanisms are unclear, gustatory dysfunction and oral frailty may increase the risk of cognitive disorders/AD through increased brain atrophy or impacts on social isolation, psychological well-being, or oral health. Understanding the associations among gustatory dysfunction, oral frailty, and AD may be critical for developing comprehensive strategies to preserve sensory and oral function, and for prevention, earlier diagnosis, and holistic management of patients with or at risk for AD.