Smoking and Alcohol Consumption are Associated with Higher Risk of Oral Cancer Incidence: A Systematic Umbrella Review

Smoking and alcohol consumption are established risk factors for oral cancer, yet the strength and consistency of their association, particularly across exposure subtypes, remain incompletely characterized in a synthesized evidence base. To assess the association of smoking and alcohol consumption with oral cancer incidence using a systematic umbrella review and meta-analysis of existing meta-analyses. MEDLINE via PubMed and Scopus/EMBASE were searched for records published up to June 2025. Association meta-analyses reporting odds ratios (OR) or relative risks (RR) with 95% confidence intervals (CI) were eligible for inclusion. Methodological quality was assessed using A Measurement Tool to Assess Systematic Reviews (AMSTAR 2), and evidence certainty was graded using the Grading of Recommendations Assessment, Development, and Evaluation (GRADE) framework. A random-effects model was applied for pooling. A total of 28 meta-analyses were included, covering approximately one million participants from 561 primary studies worldwide. Smokers had four times higher odds of oral cancer (OR=4.01, 95% CI: 3.21–4.99). Smokeless/chewed tobacco conferred a significantly greater risk (OR=5.28, 95% CI: 4.32–6.46) than the smoked type (OR=2.66, 95% CI: 1.99–3.57). Secondhand smoke exposure was also associated with elevated odds (OR=1.56, 95% CI: 1.26–1.93). Any-type alcohol consumption increased oral cancer risk (RR=2.47, 95% CI: 1.91–3.19), with a clear dose-response gradient: pooled RRs were 1.37, 2.22, and 4.94 for light, moderate, and heavy drinkers, respectively. The association of smoking and alcohol with oral cancer is statistically significant, consistent across exposure subtypes, and demonstrates a dose-response gradient, underscoring the importance of tobacco and alcohol cessation in oral cancer prevention.