Tooth loss explains income inequalities in dementia.

OBJECTIVES

Socioeconomic inequalities in oral health and dementia exist worldwide. This study investigated the mediating effects of tooth loss on the association between income and dementia.

METHODS

This study used data from the Japan Gerontological Evaluation Study, which targeted people aged ≥65 years. The explanatory variable was equivalent income in 2010. The outcome variable was dementia incidence between 2010 and 2022. Cox proportional hazard regression was used to examine the association between income and dementia incidence, adjusting for confounders. We performed causal mediation analyses to evaluate the extent to which the number of natural teeth mediates the association.

RESULTS

Among the 21,306 participants, the mean age was 73.4 years, and 53.5 % were females. The cumulative incidence of dementia was 19.7 % for people with higher incomes and 24.0 % for those with lower incomes. People with lower incomes had fewer teeth (the prevalence of having ≥20 teeth: 42.2 % in higher incomes and 31.1 % in lower incomes). Lower income was associated with dementia after adjusting for confounders (Hazard ratio (HR) [95 % confidence interval (CI)]: 1.18 [1.10; 1.26]), which was partially attenuated by controlling for the number of teeth (HR [95 % CI]: 1.17 [1.09; 1.25]). Causal mediation analysis demonstrated that the proportion mediated by the number of teeth was 6.6 %.

CONCLUSIONS

Our study found that tooth loss partially mediated the association between income and dementia. Preventing tooth loss appears to reduce inequalities in dementia among older people.

CLINICAL SIGNIFICANCE

Tooth loss has mediating effects on the association between income and dementia. Strategies for maintaining natural teeth seem effective in reducing the socioeconomic inequalities of dementia.