Effect of oral health on functional disability and mortality in older adults in Japan: a cohort study

Background
Oral health has previously shown associations with functional disability and mortality. We aimed to explore the associations of various aspects of oral health status with functional disability and mortality using survival analysis, as well as the relative magnitudes of the impact of these aspects on outcomes.
Methods
We obtained data for individuals aged 75 years and older in Shimane, Japan, who had at least one oral health check-up between April 1, 2016, and March 31, 2022 under Japan’s long-life medical care system insurance system. Those with missing data or with functional disability at baseline were excluded. 13 aspects of oral health status were assessed by dentists or dental hygienists as part of the check-up (using protocols provided by the Japan Dental Association and the Japanese Ministry of Health, Labour and Welfare): number of remaining teeth, subjective masticatory performance, objective masticatory performance, periodontal tissue status, functional dysphagia, tongue mobility, articulation, oral hygiene, number of decayed teeth, inadaptation of dentures of the upper jaw and lower jaw (considered separately), oral mucosal disease, and dry mouth. Multivariate Cox proportional hazards models were used to analyse the associations between each aspect of oral health and functional disability and mortality, with fully adjusted models adjusting for sex, age, BMI, medical history, or a propensity score derived from these covariates. Population-attributable fractions (PAFs) were calculated to assess the differential impacts of these oral health status aspects on outcome occurrence.
Findings
Of the 24 619 individuals who had an oral health check-up during the study period, 21 881 individuals were included in the analysis of functional disability (9175 [41·93%] men, 12 706 [58·07%] women, mean age 78·31 years [SD 2·88], mean follow-up 41·43 months [20·80]), and 22 747 individuals in the analysis of mortality (9722 [42·74%] men, 13 025 [57·26%] women, mean age 78·34 years [2·89], mean follow-up 42·63 months [20·58]). All 13 aspects of oral health status showed significant associations with the occurrence of mortality, while functional disability was associated with 11 aspects (excluding oral mucosal disease and dry mouth) in the fully adjusted model. Based on PAFs, of all oral health aspects assessed, objective masticatory performance had the greatest impact on both functional disability (PAF 23·10% [95% CI 20·42–25·69] for the lowest and 10·62% [8·18–12·99] for the second-lowest quartile of performance) and mortality (16·47% [13·44–19·40] and 8·90% [5·87–11·82]).
Interpretation
Various aspects of oral health are associated with mortality and functional disability. Maintaining good oral health in older adults might help to reduce these outcomes.