Revisiting the association between alcohol drinking and oral cancer in nonsmoking and betel quid non-chewing individuals

Background: Alcohol drinking is an oral cancer (OC) risk factor; tobacco smoking (TS) and betel quid chewing (BQC) are oral carcinogens and effect modifiers of drinking. Although the assessment of the independent effect of drinking on OC must necessarily account for effect modifiers, no observational study has included interaction terms between drinking, TS, BQC in regression analyses. In order to assess the independent association between drinking and OC, this pooled analysis focused on subjects who were not exposed to such effect modifiers. Methods: Case-control studies on OC, which discriminated non TS/non BQC drinkers from multiexposed drinkers were searched. Exposed subjects (≥1 drink daily, ≥10 years) were compared to unexposed subjects (non/occasional drinkers). Unadjusted odds ratios (ORs) were extracted/calculated. Pooled ORs were assessed with the random-effect method, which assumed high between-study heterogeneity (assessed with Cochran's Q). Robustness of estimates was investigated through use of adjusted ORs, correction for publication bias, sensitivity analysis to inclusion criteria. The drinking–TS interaction was assessed with the Interaction Contrast Ratio (ICR) and the Attributable Proportion due to Interaction (AP). Results: Sixteen studies were used, with substantially high heterogeneity. The pooled OR was 0.787 (95CI, 0.677–0.914). Use of adjusted ORs, correction for publication bias, sensitivity analysis corroborated these results. ICR and AP were 2.444 and 54.6%. Conclusions: Consistent with stratified analyses reporting non significant/negative associations between alcohol drinking and OC in non multiexposed subjects, an OC preventive activity of drinking is inferable. However, given the high prevalence and the oral carcinogenicity of concomitant drinking and smoking, drinking control policies remain essential.