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.