title: Allium vegetables and garlic supplements do not reduce risk of colorectal cancer, based on meta-analysis of prospective studies.
abstract: OBJECTIVE
  Laboratory studies have provided evidence that allium vegetables and garlic supplements might protect against colorectal cancer (CRC), but epidemiologic studies have produced inconsistent findings.
  
  
  METHODS
  We conducted a meta-analysis of prospective studies evaluating the associations between allium vegetables, garlic supplements, and CRC risk. We pooled effect measures using fixed- or random-effect models, assessing the highest vs the lowest intakes. We used a dose-response regression model to evaluate the relationship between allium vegetable intake and CRC risk.
  
  
  RESULTS
  Our analysis included 8 studies with 20 reports of the effects of allium vegetables (5458 patients with CRC including 7,125,067 person-years) and 5 studies with 11 reports of the effects of garlic supplements (2685 patients with CRC including 2,304,439 person-years). We found no association between higher intake of allium vegetables and CRC risk (relative risk [RR], 1.06; 95% confidence interval [CI], 0.96-1.17; P = .26). Intake of allium vegetables did not correspond to CRC risk (P for nonlinear = .24, P for linear = .20). In subgroup analysis, a higher consumption of allium vegetables was associated marginally with increased risk of colon cancer among women (RR, 1.23; 95% CI, 1.01-1.50; P = .05). Use of garlic supplements was associated significantly with an increased risk of CRC (RR, 1.18; 95% CI, 1.02-1.36; P = .03).
  
  
  CONCLUSIONS
  In a meta-analysis, we found no evidence that higher intake of allium vegetables reduced the risk for CRC. We observed that garlic supplements increased the risk for CRC, but this finding requires external validation.
authors.affiliation: State Key Laboratory of Environment Health (Incubation), Ministry of Education Key Laboratory of Environment and Health, Ministry of Environmental Protection Key Laboratory of Environment and Health, and Department of Epidemiology and Biostatistics, School of Public Health, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, China.
authors.forename: Beibei
authors.initials: B
authors.lastname: Zhu
authors.affiliation: State Key Laboratory of Environment Health (Incubation), Ministry of Education Key Laboratory of Environment and Health, Ministry of Environmental Protection Key Laboratory of Environment and Health, and Department of Epidemiology and Biostatistics, School of Public Health, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, China.
authors.forename: Li
authors.initials: L
authors.lastname: Zou
authors.affiliation: Department of Nutrition, Harvard School of Public Health, Boston, Massachusetts.
authors.forename: Lu
authors.initials: L
authors.lastname: Qi
authors.affiliation: State Key Laboratory of Environment Health (Incubation), Ministry of Education Key Laboratory of Environment and Health, Ministry of Environmental Protection Key Laboratory of Environment and Health, and Department of Epidemiology and Biostatistics, School of Public Health, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, China. Electronic address: rongzhong91@gmail.com.
authors.forename: Rong
authors.initials: R
authors.lastname: Zhong
authors.affiliation: State Key Laboratory of Environment Health (Incubation), Ministry of Education Key Laboratory of Environment and Health, Ministry of Environmental Protection Key Laboratory of Environment and Health, and Department of Epidemiology and Biostatistics, School of Public Health, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, China. Electronic address: miaoxp@mail.hust.edu.cn.
authors.forename: Xiaoping
authors.initials: X
authors.lastname: Miao
mesh_terms: D000328:Adult; D000368:Aged; D000490:Allium / Q000009:adverse effects / Q000378:metabolism*; D003106:Colon; D015179:Colorectal Neoplasms / Q000453:epidemiology* / Q000517:prevention & control*; D004032:Diet / Q000379:methods*; D005260:Female; D005737:Garlic; D006801:Humans; D008297:Male; D008875:Middle Aged; D011446:Prospective Studies; D018570:Risk Assessment; D014675:Vegetables
keywords: Cancer Risk Factor; Diet; Prevention; Review