To investigate the association between tooth loss and the incidence of mild cognitive impairment (MCI) and dementia, focusing on diet quality as a potential mediator.

Prospective cohort study.

Community-dwelling older men enrolled in the Northern Ireland PRIME study (Prospective Epidemiological Study of Myocardial Infarction).

A group of men, aged 58–71 years, underwent dental examinations in 2001–2003. Surviving participants were invited to attend a cognitive rescreening in 2016–2020, which included a food frequency questionnaire. Cognitive outcomes were categorised as normal, MCI or dementia, based on standardised neurocognitive tests. Dietary diversity scores (DDS) were calculated based on the frequency of intake of food groups. Analyses included multiple logistic regression to evaluate the associations between tooth loss, defined as <20 remaining natural teeth, and MCI/dementia incidence adjusting for potential confounders. Mediation analysis assessed the role of diet quality in this relationship.

A total of 628 men were included, with a mean baseline age of 63.2 years (SD 2.8) and a median follow-up of 15.0 years (IQR 14.2–17.0). At rescreening, 485 (77.2%) were cognitively normal, 112 (17.8%) had MCI, and 31 (4.9%) had dementia. In fully adjusted models, tooth loss was significantly associated with MCI/dementia (OR = 2.06, 95% CI 1.20–3.55, p < 0.01). DDS partially mediated this relationship, explaining approximately 23% of the total effect.

In this cohort of older men, tooth loss was associated with incidence of MCI/dementia over 15 years, and diet diversity partially mediated this association. These findings highlight an important pathway connecting oral health, dietary quality, and cognitive outcomes.