Allium vegetables and risk of prostate cancer: evidence from 132,192 subjects.

OBJECTIVE: To evaluate the relationship between allium vegetable intake and risk of prostate cancer. METHODS: A systematic literature search up to May 2013 was carried out in PubMed, EMBASE, Scopus, Web of Science, Cochrane register, and Chinese National Knowledge Infrastructure (CNKI) databases, and the references of retrieved articles were also screened. The summary relative risks with 95% confidence interval for the highest versus the lowest intake of allium vegetables were calculated. Heterogeneity and publication bias were also evaluated. RESULTS: A total of nine epidemiological studies consisting of six case-control and three prospective cohort studies were included. We found a significantly decreased risk of prostate cancer for intake of allium vegetables (OR = 0.82, 95% CI 0.70, 0.97). Moreover, in the subgroup analysis stratified by allium vegetable types, significant associations were observed for garlic (OR = 0.77, 95% CI 0.64-0.91) but not onions (OR = 0.84, 95% CI 0.62-1.13). CONCLUSIONS: Allium vegetables, especially garlic intake, are related to decreased risk of prostate cancer. Because of the limited number of studies, further well-designed prospective studies are warranted to confirm the findings of our study.