Tobacco advertising and oral health among never smokers: the mediating role of secondhand smoke exposure

Objective: To determine whether the association between tobacco advertising (TA) exposure and poor self-rated oral health (SROH) is mediated through secondhand smoke (SHS) exposure in Brazilian adults who have never smoked. Methods: Secondary cross-sectional analysis of The Brazilian National Health Survey 2019 data. The daily, weekly, or monthly exposure to SHS at home or at work was set as the mediator. Mediation analysis within a counterfactual approach used adjusted binary logistic regressions for both poor SROH and SHS exposure, to estimate the natural direct effect (NDE), natural indirect effect (NIE) through SHS exposure, and marginal total effect (MTE) of TA exposure on poor SROH. To assess the robustness of the results, we calculated the E-value for the MTE. Results: The sample comprised 53,295 never smoker adults. The MTE of TA exposure on poor SROH was 1.09 (1.03, 1.16), with the indirect effect through SHS exposure responsible for only 16.6% of the total (NIE: 1.01 [1.01, 1.02] and NDE: 1.08 [1.02, 1.14]). An effect of 1.42 would be required for an unmeasured confounder to explain away the association between TA and SROH. Conclusion: More individuals exposed to TA have poor SROH than those unexposed, with secondhand smoke exposure explaining only a small portion of this effect. Upstream tobacco policies should consider oral health outcomes. Keywords: oral health, self-assessment, tobacco industry, tobacco smoke pollution, mediation analysis