No association between garlic intake and risk of colorectal cancer

Abstract

Background Although experimental studies suggested beneficial role of garlic intake on colorectal carcinogenesis, limited prospective cohort studies have evaluated garlic intake in relation to colorectal cancer (CRC) incidence. Methods We followed 76,208 women in the Nurses’ Health Study and 45,592 men in the Health Professionals Follow-up Study for up to 24 years and examined garlic intake and garlic supplement use in relation to CRC risk. Information on garlic intake and supplement use was assessed using a validated food frequency questionnaire and a Cox proportional hazard regression model was used to estimate the multivariable hazard ratio (MV-HR) and 95% confidence intervals (95% CIs). Results We documented 2,368 (1,339 women and 1,029 men) incident CRC cases and found no association between garlic intake and CRC risk; the MV-HRs (95% CIs) associated with garlic (1 clove or 4 shakes per serving) intake ≥1/day compared with <1/month were 1.21 (0.94–1.57; p-trend=0.14) for women and 1.00 (0.71–1.42; p-trend=0.89) for men. The MV-HRs (95% CIs) of CRC for garlic supplement use, which was used in 6% of the participants in each study, were 0.72 (0.48–1.07) for women and 1.22 (0.83–1.78) for men. Conclusion Our prospective data do not support an important role of garlic intake or garlic supplement use in colorectal carcinogenesis.

Garlic consumption and colorectal cancer risk in man: a systematic review and meta-analysis

“…Therefore only fourteen studies met the inclusion criteria: seven were case-control (22)(23)(24)(25)(26)(27)(28) and seven were cohort studies (29)(30)(31)(32)(33)(34)(35) (Table 1). Among the cohort studies two considered garlic supplements only (31,33) , while among the other five studies two considered garlic supplements in addition to dietary intake (34,35) . Table 1 summarizes the detailed characteristics of included studies.…”

“…Three studies reported findings only for females (22,30,32) , one only for males (29) , eight for females and males together (23,(25)(26)(27)(28)31,33,34) and three presented findings for males and females separately (24,34,35) . Three studies reported results of risk for rectal cancer (22,31,35) , six for colon cancer (23,(29)(30)(31)(32)35) and eight for CRC (24)(25)(26)(27)(28)(33)(34)(35) . Study-specific quality scores of each study are summarized in Supplemental Table S1 and Supplemental Table S2 for case-control and cohort studies, respectively (see online supplementary material).…”

“…Our results are in contrast with a previous meta-analysis based on seven studies, four casecontrol (22)(23)(24)(25) and three cohort (29)(30)(31) , which suggested a preventive effect and estimated that high consumption of garlic decreases the risk of CRC by 30 % (11) . In comparison with the previous meta-analysis, our updated search identified and included seven more studies (26)(27)(28)(32)(33)(34)(35) which may be responsible for these discrepancies. In addition, our analysis included the estimated risks associated with the use of garlic supplements which were excluded in the previous …”

Dietary Bioactive Diallyl Trisulfide in Cancer Prevention and Treatment

“…Conversely, there are instances of null findings in some stand-alone cohort studies [ 18 , 19 ] and in meta-analyses evaluations of cohort studies [ 11 , 12 ]. Two cohort studies reporting a null association between garlic intake and colorectal cancer analyzed the Nurses’ Health Study, Health Professionals Follow-Up Study, and Cancer Prevention Study II Nutrition Cohort [ 18 , 19 ]. It is worth noting that these studies used self-administered food frequency questionnaires and considered a serving of garlic as one clove or four shakes of garlic powder or garlic salt [ 18 , 19 ].…”

“…Two cohort studies reporting a null association between garlic intake and colorectal cancer analyzed the Nurses’ Health Study, Health Professionals Follow-Up Study, and Cancer Prevention Study II Nutrition Cohort [ 18 , 19 ]. It is worth noting that these studies used self-administered food frequency questionnaires and considered a serving of garlic as one clove or four shakes of garlic powder or garlic salt [ 18 , 19 ]. It is possible that use of garlic powder and garlic salt within these studies accounted for intake without providing the same protective effect as fresh garlic cloves [ 18 , 20 ].…”