Number of natural teeth and incident cognitive impairment in older Chinese adults

Abstract

This study aimed to examine the longitudinal association between baseline number of natural teeth and incident cognitive impairment among older Chinese adults in the Chinese Longitudinal Healthy Longevity Survey and explore whether dietary diversity partially mediated this association. We included 4364 participants from the 2008 Chinese Longitudinal Healthy Longevity Survey who were free of cognitive impairment at baseline and had at least 1 follow-up cognitive assessment through 2018. Incident cognitive impairment was defined as a Mini-Mental State Examination Score <24 at any follow-up assessment. Cox proportional hazards models were used to estimate hazard ratios (HRs) and 95% confidence intervals (CIs) for the association between baseline number of natural teeth and incident cognitive impairment, with tooth count modeled both continuously per interquartile range (20 teeth) increase and categorically by quartiles. Restricted cubic spline analyses were performed to examine potential nonlinearity, and subgroup analyses with multiplicative interaction tests were conducted to assess potential effect modification. Over a median follow-up of 6 years (24,585 person-years), 1835 participants (42.0%) developed incident cognitive impairment. In the fully adjusted model, each interquartile range increase in natural teeth was associated with a lower risk of incident cognitive impairment (HR = 0.86; 95% CI: 0.78–0.95; P = .002); participants in the highest tooth-count quartile had a lower risk than those in the lowest quartile (HR = 0.81; 95% CI: 0.70–0.93; P = .004). Restricted cubic spline analysis supported an overall association ( P = .013) without evidence of nonlinearity ( P = .467). Age modified the association ( P for interaction = .043); the association was evident among participants aged ≥70 years (HR = 0.73; 95% CI: 0.66–0.82) but not among those aged <70 years (HR = 0.95; 95% CI: 0.75–1.19). Exploratory mediation analysis suggested a small indirect effect through Dietary Diversity Score (indirect effect = 0.0012; 95% bootstrap CI: 0.0001–0.0024), accounting for approximately 9.9% of the total association. A higher baseline number of natural teeth was associated with a lower risk of incident cognitive impairment among older Chinese adults. Exploratory mediation analysis suggested that dietary diversity may account for a small part of the association between natural tooth count and mean follow-up Mini-Mental State Examination. These observational findings do not establish causality and warrant further investigation.