Interrelationships between Refined Carbohydrates, Periodontal Diseases, and Cognitive Decline: A Narrative Review.

Accumulating studies suggest that carbohydrate quality influences both oral and cognitive health. Diets rich in refined carbohydrates promote insulin resistance, oxidative stress, inflammation, and disrupt oral microbiota. These changes contribute to periodontal disease and neurodegeneration. Periodontitis is associated with cognitive decline via inflammation, bacterial translocation, and blood-brain barrier disruption. Although less extensively studied, reverse pathways may also operate. Cognitive decline may alter dietary behavior through neurohormonal changes, increasing preference for sweeter foods, and promoting periodontal disease by impairing motor functions essential for oral hygiene. Periodontitis may further shift dietary choices toward softer, more processed foods through tooth loss, oral pain, and chewing difficulties. These interactions may reinforce a cycle linking diet, oral health, and cognition. To date, no study has comprehensively examined the interrelationships between carbohydrate quality, periodontal disease, and cognitive decline within a unified framework. This narrative review aimed to address this gap by synthesizing findings on each bidirectional dyadic association, examining terminology and methodological approaches, and discussing shared mechanisms and biological pathways. Through this work, insulin resistance, chronic inflammation, oxidative stress, and microbiota dysbiosis were identified as shared integrative pathways, and key research gaps were highlighted to guide future research and inform prevention strategies for aging populations.