Oral Health and Social Isolation After 6 Years: Mediation of Oral Functions

Objectives Tooth loss was longitudinally associated with social isolation. The absence of dental prosthesis use was an additional risk factor. However, the mediating pathways for this association are unknown. The aim of this cohort study was to estimate the mediating effect of three oral functions: speaking, smiling and chewing observed at baseline on the association between oral health at baseline and social isolation after 6 years of follow‐up. Methods The 2010–2016 panel data from 6103 functionally independent participants aged ≥ 65 years who were not socially isolated at baseline was used from the Japan Gerontological Evaluation Study (JAGES). Causal mediation analysis using parametric logistic regression models was used to calculate the natural direct effect (NDE), the natural indirect effect (NIE), and the total effect. Social isolation was derived from a 5‐point index and dichotomised (0/3 = not isolated, 4/5 = isolated). The confounders observed at baseline were age, sex, educational attainment, income, activities of daily living, living area, and having depressive symptoms assessed using the geriatric depression scale (GDS‐15). Results The mean age of the participants was 72.4 years (SD = ±5.1), and 44.7% were males. Social isolation was observed at follow‐up among 3.6% of participants ( n = 220). The cumulative incidence rate of socially isolated participants among those with ≥ 20 teeth was 2.9% increasing gradually to 3.2%, 3.5%, 3.7% and 7.2% among those with 10–19 teeth and used dental prosthesis, 10–19 teeth and did not use the dental prosthesis, 0–9 teeth and used dental prosthesis, and 0–9 teeth and did not use the dental prosthesis respectively. Compared with those with ≥ 20 teeth, having difficulty in speaking [NIE odds ratio (OR) = 1.02, 95% confidence interval (CI) = 0.93–1.11], problems in smiling (NIE OR = 1.02, 95% CI = 0.93–1.10) and difficulty in chewing (NIE OR = 1.04, 95% CI = 0.94–1.14) might have mediated the association for those with 10–19 teeth and used dental prosthesis as well as for those with 10–19 teeth without dental prosthesis (NIE OR = 1.02, 95% CI = 0.94–1.10), (NIE OR = 1.02, 95% CI = 0.93–1.11) and (NIE OR = 1.02, 95% CI = 0.93–1.11) respectively. While they might not have mediated the association for those with 0–9 teeth with and without dental prosthesis use. Conclusion With low precision and uncertain estimates, limited oral function might have mediated the association between tooth loss (10–19 with and without dental prosthesis use groups) and social isolation over 6 years. It was uncertain whether a mediation effect of oral functions was observed for those with 0–9 teeth with and without dental prosthesis use.