Mapping the Oral–Nutrition–Brain Axis in Aging: A Scoping Review of Evidence Linking Oral Health, Nutrition, and Cognitive Outcomes

Background: Oral health, nutrition, and neurocognitive health are increasingly recognized as components of healthy aging; however, their multidimensional relationships and plausible biological connections relevant to Alzheimer’s disease and related dementia (AD/ADRD) risk remain incompletely characterized. Objective: To systematically map evidence linking oral conditions and function, nutrition-related factors and biomarkers, and neurocognitive outcomes in adults aged ≥65 years, and conceptualize an integrative Oral–Nutrition–Brain Axis (ONBA). Methods: This scoping review followed Joanna Briggs Institute methodology and PRISMA-ScR guidance. Five electronic databases were searched for studies published from 2010 through June 2025. Evidence was harmonized across oral and functional indicators, nutritional/metabolic/inflammatory biomarkers, and neurological and cognitive outcomes. Results: Of 3415 records identified, 1988 unique records were screened, and 120 studies met eligibility criteria. Evidence was predominantly observational and geographically concentrated in East Asia. Periodontal inflammation, compromised dentition, impaired functional occlusion and masticatory performance were consistently associated with nutritional vulnerability, poorer cognitive performance, cognitive decline, and adverse AD/ADRD outcomes. Co-occurring nutritional and systemic markers included low body weight, hypoalbuminemia, low serum vitamin B12 and folate, hyperhomocysteinemia, and elevated inflammatory biomarkers. Mapped findings aligned across three proposed conceptual frameworks: inflammatory–microbial, nutritional–metabolic, and sensorimotor deafferentation axes. Studies incorporating neuroimaging biomarkers or integrating all three ONBA domains simultaneously remained limited. Conclusions: Oral health and functional dentition may represent key modifiable proxies associated with nutritional and neurocognitive vulnerability in older adults. Longitudinal studies incorporating harmonized oral, nutritional, inflammatory, and neurological phenotypes are needed to clarify temporal sequence, evaluate potential explanatory relationships, and inform multi-domain risk assessment for healthy cognitive aging.