Poor oral health may increase dementia risk through both biological and social pathways, as reported by researchers from Science Tokyo. Drawing on recent epidemiologic research, the team highlights how eating and speaking difficulties might act as overlooked social mechanisms that may amplify risk by contributing to social isolation. Moreover, in a longitudinal study, they also found that poor oral health is a strong predictor of weight loss in older adults.
As people get older, oral health tends to deteriorate if it is not adequately maintained. Common problems like tooth loss, jaw weakness, or dry mouth can affect basic oral functions, including chewing, swallowing, and even speaking. While these issues can often be managed effectively thanks to advances in modern medicine, poor oral health can still set the stage for severe conditions and disorders.
Many studies, for example, have found associations between poor oral health and dementia. The underlying mechanisms behind this relationship are not very clear; however, scientists don't know for certain which condition causes the other. Moreover, most research efforts on this topic have focused on exploring purely biomedical mechanisms, such as how elevated levels of inflammatory molecules and oral bacteria might affect the brain or the immune system and thereby prime the body for dementia. Much less attention has been paid to the social aspects related to oral function (such as speaking) and to whether they could also be implicated in neurodegeneration.
Against this backdrop, a research team led by Professor Jun Aida from the Department of Dental Public Health, Graduate School of Medical and Dental Sciences, Institute of Science Tokyo (Science Tokyo), Japan, conducted a literature review on the topic, condensing information from the latest epidemiologic studies. Their work, published in the Journal of Dental Research on October 18, 2025, synthesizes recent advances in causal inference techniques to theoretically and methodologically clarify the association between oral health and dementia.
The team noted that many studies considered a possible bidirectional relationship between oral health and dementia and used repeated surveys over time to clarify the direction of causality. However, cognitive function prior to the first survey was often overlooked; this could be an important metric given that it affects the risk of poor oral health in old age and thus acts as a confounding factor. The researchers also provide explanations of studies that have addressed this important issue.
Most importantly, the researchers propose that difficulties with eating and speaking could be key potential mechanisms. "These functions have a social aspect that facilitates interpersonal interactions and can reduce social isolation," explains Aida. "When we consider the multilayered direct and indirect mechanisms leading to dementia throughout life, we find that poor oral health possibly increases the risk of dementia through social isolation via eating and speaking problems."
In addition to this literature review, Aida and colleagues also conducted a six-year longitudinal study involving over 3,000 older Japanese adults, aiming to clarify the relationship between oral frailty and weight loss. This work, published in the Journal of Dental Research on August 16, 2025, revealed that chewing difficulty was the strongest predictor of weight loss among the various components that define oral frailty, such as dry mouth and missing teeth.
Overall, these findings strongly support the idea that poor oral health can have deeper ramifications that ultimately affect the entire body. "Together, our papers provide important evidence that oral health affects not only the teeth and mouth, but also broader aspects of health, including brain function, nutritional status, and social engagement," concludes Aida. More research efforts will be needed to further clarify these intricate relationships and determine effective interventions.
