Association between tooth loss and cognitive impairment in community-dwelling older Japanese adults: a 4-year prospective cohort study from the Ohasama study

Background Numerous prospective studies have investigated the association between the number of remaining teeth and dementia or cognitive decline. However, no agreement has emerged on the association between tooth loss and cognitive impairment, possibly due to past studies differing in target groups and methodologies. We aimed to investigate the association between tooth loss, as evaluated through clinical oral examinations, and the development of cognitive impairment in community-dwelling older adults while considering baseline cognitive function. Methods This 4-year prospective cohort study followed 140 older adults (69.3% female) without cognitive impairment aged ≥65 years (mean age: 70.9 ± 4.3 years) living in the town of Ohasama, Iwate Prefecture, Japan. Cognitive function was evaluated with the Mini-Mental State Examination (MMSE) in baseline and follow-up surveys. Based on a baseline oral examination, the participants were divided into those with 0–9 teeth and those with ≥10 teeth. To investigate the association between tooth loss and cognitive impairment, we applied a multiple logistic regression analysis adjusted for age, sex, hypertension, diabetes, cerebrovascular/cardiovascular disease, hypercholesterolemia, depressive symptoms, body mass index, smoking status, drinking status, duration of education, and baseline MMSE score. Results In the 4 years after the baseline survey, 27 participants (19.3%) developed cognitive impairment (i.e., MMSE scores of ≤24). Multiple logistic regression analysis indicated that participants with 0–9 teeth were more likely to develop cognitive impairment than those with ≥10 teeth were (odds ratio: 3.31; 95% confidence interval: 1.07–10.2). Age, male gender, and baseline MMSE scores were also significantly associated with cognitive impairment. Conclusions Tooth loss was independently associated with the development of cognitive impairment within 4 years among community-dwelling older adults. This finding corroborates the hypothesis that tooth loss may be a predictor or risk factor for cognitive decline.