Frailty mediated the association between tooth loss and mortality in the oldest old individuals: a cohort study

Abstract Background: The relationship between tooth loss and mortality risk remains uncertain, necessitating further investigation. This study aimed to examine whether frailty acts as a mediator in the association between tooth loss and mortality risk in the oldest old population. Methods: The Chinese Longitudinal Healthy Longevity Survey was utilized to track participants from 1998 to 2018. Tooth loss was evaluated based on the initial number of remaining teeth, while frailty was determined using a composite of 30 indicators. The variables of mortality, frailty, and tooth loss were assigned as the outcome, mediator, and independent variable, respectively. The Cox model was utilized to incorporate potential confounding factors for the purpose of conducting causal mediation analysis. Various measures were computed, including the total effect (TE), average causal mediation effect (ACME), average direct effect (ADE), and proportion mediated (PM). Results: The study encompassed a total of 129,936 person-years at risk, with a sample size of 31,899 individuals who had a mean age of 91.79 years. The TE and ADE of tooth loss on mortality were estimated to be 0.12 (95%CI: 0.08, 0.15) and 0.09 (95%CI: 0.05, 0.13), respectively. Additionally, the ACME of frailty was found to be 0.03 (95%CI: 0.02, 0.03), with 21.56% of the TE being mediated. In the subgroup analysis, the ACME of frailty accounted for 33.64% (P=0.28) of the TE among individuals aged 75-89 years, 30.63% (P<0.01) among those aged 90-100 years, and 38.61% (P<0.01) among those above 100 years. Furthermore, the ACME of frailty accounted for 27.38% (P<0.01) of the TE among men and 19.62% (P<0.01) among women. Conclusion: This study demonstrated a significant association between tooth loss and mortality, with frailty acting as a mediator in this relationship. It is recommended that oral health indicators and frailty status be incorporated into routine geriatric assessments to promote optimal oral health and non-frailty status.