Abstract B101: Garlic consumption and colorectal cancer risk in the CPS-II Nutrition Cohort
Authors: McCullough Marjorie L. , Jacobs Eric J. , Shah Roma , Campbell Peter T. , Gapstur Susan M. 
Published: June 2012

Abstract
Background: The World Cancer Research Fund/American Institute for Cancer Research considers a role for garlic in colorectal cancer prevention to be “probable”. This conclusion is based on supportive preclinical evidence and pooled analyses of high vs low consumption from two prospective cohort (RR=0.72, 95% CI 0.54–0.96) and five case control (RR=0.76, 95% CI 0.58–0.98) studies. The two prospective studies included &lt;300 cases each, and the highest category of garlic consumption considered was ≥1 or ≥2 servings per week compared to none. We examined the association between garlic consumption and risk of colorectal cancer in a large, nationwide prospective cohort study including over 1100 colorectal cancer cases. This large study allowed for a more detailed analysis of garlic intake including at least daily consumption.
Methods: In 1999, 43,025 male and 57,043 female participants in the Cancer Prevention Study (CPS)-II Nutrition Cohort with no history of cancer completed food frequency questionnaires in which frequency of garlic consumption was assessed. Garlic supplement use was assessed in 2001. Participants were followed for incident colorectal cancer through mid-2007 via biennial questionnaires and cases were verified by medical record abstraction or linkage to state tumor registries. Cox proportional hazards regression methods were used to estimate hazard rate ratios (HRs) and 95% confidence intervals (CIs). Potential non-dietary and dietary confounders included in the models were age, history of endoscopy, NSAID use, recreational physical activity, body mass index, smoking, HRT use (women), red and processed meat consumption, fruit and vegetable consumption and total calcium intake.
Results: Incident colorectal cancer was verified in 595 men and 559 women. Five percent of participants reported garlic consumption (1 clove or 4 shakes) 1 or more times per day in 1999, and in 2001, and 5% reported currently using garlic supplements. Dietary garlic consumption was not related to colorectal cancer risk in men. Among women, compared to consumers of dietary garlic less than once per month, never consumption of garlic was associated with a lower risk of colorectal cancer (RR=0.74, 95% CI 0.57–0.96); similarly, regular consumption of garlic was associated with a lower risk of incident colorectal cancer (HR1 time/wk=0.80, 95% CI 0.60–1.07; HR2–4 times/wk=0.65, 95% CI=0.48–0.87; HR5–6 times/wk=0.61, 95% CI=0.40–0.94 and HR1+ times/day=0.72, 95% CI 0.47–1.10). Garlic supplement use (current use at least once/week vs never) was not related to colorectal cancer risk in men or women. These associations did not vary by colorectal sub-site, BMI or HRT use (among women).
Conclusion: This study does not support the hypothesis that garlic intake or supplement use reduces colorectal cancer risk in men, but suggests an inverse association with greater dietary intake among women who consume garlic. The reasons for different associations by sex, and for lower risk in female non-consumers are unclear and deserve further study.
Citation Information: Cancer Prev Res 2011;4(10 Suppl):B101.