The role of differential exposure and susceptibility to heavy drinking linking income inequalities and tooth loss: An investigation of the alcohol harm paradox using a four-way decomposition analysis.

ABSTRACT

OBJECTIVES: To examine the extent to which the effect of income inequalities on tooth loss is attributable to differential exposure and susceptibility to heavy drinking in older Brazilian adults. METHODS: We conducted a secondary analysis using data from The Brazilian Longitudinal Study of Ageing (ELSI-Brazil 2015-2016), a nationally representative sample of community-dwelling people aged 50 years and over. Causal mediation analysis based on the counterfactual outcome framework decomposed the effect of income on tooth loss mediated by heavy drinking into four components (four-way decomposition) controlled direct effect (neither mediation nor interaction), reference interaction (interaction only), mediated interaction (both mediation and interaction) and pure indirect effect (mediation only). Proportions of effect attributable to each component were calculated to estimate the differential exposure (the sum of the third and fourth components) and differential susceptibility (the sum of the second and third components) to heavy drinking. RESULTS: The analytical sample comprised 8114 participants. After adjusting for covariates, 7.3% (95% CI 3.8%; 10.9%) and -39.5% (95% CI -75.8%; -3.3%) of the effects of income on tooth loss were attributable to differential exposure and susceptibility to heavy drinking, respectively, consistent with the alcohol harm paradox. When setting non-functional dentition as outcome, only the effect of differential susceptibility remained (-81.7% [95% CI -128.2%; -35.2%]). CONCLUSION: Our findings suggest that individuals of low-income groups appear to be more susceptible to the effects of heavy drinking on tooth loss.