Allium vegetables and upper aerodigestive tract cancers: a meta-analysis of observational studies

Scope To provide updated quantitative overall estimations of the relation between total allium, garlic, and onion intake on the risk of cancer of the upper aerodigestive tract (UADT). Methods and results We combined data of published observational studies (21 case–control and four cohort studies), using a meta‐analytic approach and random effects models. The overall relative risks (RR) and 95% confidence intervals (CIs) for the squamous cell carcinoma of the UADT were 0.79 (95% CI 0.56–1.11) for total allium, 0.74 (95% CI 0.57–0.95) for garlic, and 0.72 (95% CI 0.57–0.91) for onion for the highest versus the lowest consumption. The inverse relation was apparently stronger in case–control studies (RR 0.56, 95% CI 0.38–0.83 for total allium), in Chinese studies (RR 0.67, 95% CI 0.45–0.98 for garlic intake), and for esophageal than for head and neck cancers. Apparently, there was no relation between allium vegetable intake and adenocarcinoma of the esophagus. Conclusion We found a moderate inverse association between allium vegetable intake and the risk of squamous cell carcinoma of the UADT in case–control studies. The relation was unclear in cohort studies and for adenocarcinoma of the esophagus.