Smoking, drinking, tooth loss and risk of oral–pharyngeal cancer mortality

• We investigated the association between smoking, alcohol consumption, and the number of teeth for oral and pharyngeal cancer mortality. • Both smoking and drinking were associated with a higher risk of oral and pharyngeal cancer mortality, particularly among those with fewer teeth. • Monitoring these high-risk populations in both clinical and community settings is necessary. Smoking and alcohol consumption are major risk factors for oral and pharyngeal cancer (OPC) mortality. However, the interaction between these risks and tooth loss, as an indicator of cumulative consequences of oral health disadvantages, has not been investigated. We used data from the Japan Gerontological Evaluation Study, which included functionally independent Japanese adults aged ≥ 65 years. The baseline survey was conducted in 2010 and followed up until 2022. The outcome was OPC mortality. The exposures were smoking, drinking, and the number of teeth. To estimate the hazard ratio (HR) and 95% confidence interval (CI) of OPC mortality, the Cox proportional hazards model was applied. We also assessed multiplicative and additive interactions by calculating the relative excess risk due to interaction (RERI). A total of 39,882 participants were included (men: 46.8%). The mean age at baseline was 73.7 years (SD = 6.0). The mean follow-up was 3,689 days. Among them, 0.2% had OPC mortality. Both smoking and drinking were associated with a higher risk of OPC mortality compared with none (HR, 2.87; 95%CI, 1.26–6.55). Those with 0–19 teeth were associated with a higher risk of OPC mortality than those with ≥ 20 teeth (HR, 1.96; 95%CI, 1.11–3.46). Interaction analysis showed higher OPC mortality risk among those with both smoking and drinking and 0–19 teeth (multiplicative interaction; HR, 5.02; 95%CI, 1.09–23.21, additive interaction; RERI, 2.97; 95%CI, 0.06–5.88). Both smoking and drinking were associated with a higher risk of OPC mortality, particularly among those with fewer teeth.