Oral frailty as a risk factor for mild cognitive impairment in community-dwelling older adults: Kashiwa study.

Background: Oral frailty is defined as a slight decline in comprehensive oral function and can predict the onset of adverse health outcomes including morbidity in community-dwelling older adults. Previously, the number of remaining teeth and masticatory status had been suggested to be associated with cognitive decline. The effects of comprehensive oral condition on cognitive decline have not been adequately examined. In this study, we aimed to examine whether oral frailty is associated with new-onset mild cognitive impairment (MCI) among community-dwelling older adults.

Methods: Two thousand and forty-four participants of a longitudinal cohort study in Kashiwa City, Chiba Prefecture, without cognitive decline who participated in at least one follow-up survey, were included. New-onset MCI was assessed using the Mini-Mental State Examination (score < 27 defined as MCI). Oral frailty was evaluated based on six components including the number of remaining teeth, masticatory status, tongue pressure, oral motor skills, and subjective difficulties in eating and swallowing. "Oral non-frailty" was defined as good performance on all six measures, "oral pre-frailty" was defined as poor performance on one or two measures, and "oral frailty" was defined as poor performance on three or more measures. Statistical analysis was performed, mainly using a Cox proportional hazards model.

Results: Of the 1410 participants who did not fit the exclusion criteria (mean 72.4 ± 5.2 years; 49 % female), 19 % had new-onset MCI during the follow-up period. When comparing the status of oral frailty (non-frailty, oral pre-frailty, and oral frailty), the oral frailty group had a significantly higher hazard ratio for new-onset MCI than the other groups, even after adjusting for confounding factors. Among the six components, a decrease in the number of remaining teeth, low tongue pressure, and difficulty eating tough foods significantly correlated with new-onset MCI. Additionally, we found individuals with co-existing oral frailty and physical frailty to be associated with an increased risk of MCI. However, no significant increase in hazard ratio was observed in participants with either physical or oral frailty.

Conclusions: The study findings suggest that oral frailty could predict the risk of new-onset MCI in community-dwelling older adults. Further, we found that oral frailty with physical frailty exacerbated this risk, implying the existence of direct or additive effects on cognitive dysfunction. Comprehensive oral health focusing on maintaining eating function can be a strategy to prevent MCI and delay dementia in community-dwelling older adults.