The association between dentition status and cognitive performance : a multi-population investigation

Abstract

Dementia, particularly Alzheimer's disease (AD) as its most prevalent form, represents a major public health issue. Affecting 24 million people globally, AD cases are projected to double every 20 years until 2040. The disease's management costs and care requirements create substantial burdens for patients, families, and healthcare systems.

Teeth are crucial for oral function and quality of life. Tooth loss impairs chewing, potentially leading to malnutrition, speech difficulties, and social withdrawal. Over the past decade, it has also been identified as a global health concern due to its association with cognitive decline. Nevertheless, the interplay between tooth loss and neurocognitive performance, as well as the possible mediators and moderators, is still not well explored.

To bridge this gap in understanding, we initially reassessed the prevailing epidemiological patterns of AD and edentulism, respectively. Study results revealed that the prevalence rate of AD in China has grown by 28% from 1990 to 2021, with a projected 60% rise expected by 2040. Regarding edentulism, the diminution in the annual percentage change in prevalence, incidence, and Disability-Adjusted Life Years (DALY) rates confirmed the achievement of previous interventions from 1990 to 2021. Nevertheless, due to the aging population, a significant burden of edentulism persists, as reflected by an increasing prevalence rate which is expected to persist over the next twenty years.

Following this, we conducted a systematic review to explore the interplay between tooth loss and reduced cognitive capacity. The findings from longitudinal studies indicated that tooth loss could be a possible contributing factor for cognitive impairment. Subsequently, we examined two demographic studies obtaining data from the National Health and Nutrition Examination Survey (NHANES) to assess the impact of cholesterol levels and dietary inflammation on the interconnection between tooth loss and reduced cognitive function. Both studies confirmed strong relationship among tooth loss and cognitive capacity. The first study revealed that high-density lipoprotein cholesterol (HDL-C) levels functioned as a mediator in the relationship between impaired dentition and cognitive capacity. The second study demonstrated that changes in dietary patterns related to tooth loss had an impact on cognitive impairment, a process that can be moderated by serum albumin levels.

Building upon these discoveries, we delved deeper into the influence of tooth loss on metabolic and dietary profiles concerning cognitive performance within the Hong Kong population. Cholesterol, CRP, and albumin levels did not show significant involvement in shaping the connection between tooth loss and cognitive function. The key findings observed in the US population were not replicated in the Hong Kong population, suggesting that these results may not be generalizable worldwide. Nevertheless, the outcomes demonstrated an interplay between impaired dentition and cognitive performance, highlighting that controlling glucose levels could mitigate the impacts of tooth loss on cognitive function regardless of dietary habits.

This thesis represents the initial in-depth assessment of potential mediating and moderating factors in the link between tooth loss and cognitive performance. The results could serve as a basis for forthcoming research exploring the complex relationship between impaired dentition and cognition.