Written by Edzard Ernst and the CAM-Cancer Consortium.
Updated September 29, 2011

Garlic (Allium sativum)

Does it work ?

The literature on garlic (Allium sativum) as a means of reducing cancer risk is huge. Therefore, the following section is mainly based on up-to-date, authoritative reviews.

Reviews

Most of the evidence for garlic as a cancer preventative in humans rests, of course, on epidemiological data.

A meta-analysis of all cohort and case control studies suggested that the regular intake of garlic reduces the cancer risk: the relative risk for colon cancer was 0.69 (95% CI = 0.55-0.89) for stomach cancer it was 0.53 (95% CI – 0.31-0.92)11. Because of heterogeneity between data sets, the authors' conclusion was cautious: "high intake of garlic may be associated with a protective effect against stomach and colorectal cancer"11.

A subsequent review included more studies and related to all types of cancer12. The authors found no protective effect for gastric, breast, lung or endometrial cancer. Limited evidence was found for an inverse relationship between garlic consumption and the risk of colon, prostate, oesophageal, larynx, oral, ovary or renal cancers.

A more recent epidemiological cohort-study of ~ 7700 men and women aged 50-76 years and 5 years of follow-up associated regular garlic intake with a significantly elevated colorectal cancer risk13.

Clinical trials

Relatively few clinical trials of garlic to prevent cancer are available23-27. Their key data are summarized in table 1. Collectively these studies fail to show conclusively that garlic-intake reduces the cancer risk.

Pre-clinical studies

Garlic’s mechanisms of action have been studied extensively. At least 5 major pathways have been identified for each of which the evidence is substantial and sound.
Modulation of carcinogen metabolism
Inhibition of cell cycle progression
Induction of apoptosis
Histone modification
Inhibition of angiogenesis
Modification of drug metabolising enzymes especially the family of the hepatic cytochrome P450 (CYP) enzymes2
Immunomodulatory activity2
Many of the findings from animal studies support these postulated mechanisms14

Citation

Edzard Ernst, CAM-Cancer Consortium. Garlic (Allium sativum) [online document]. http://www.cam-cancer.org/CAM-Summaries/Herbal-products/Garlic-Allium-sativum. September 29, 2011.

Document history

References

  1. Ernst E, Pittler MH, Wider B, Boddy K. The Desktop Guide to Complementary and Alternative Medicine. 2nd edition. Edinburgh: Elsevier Mosby. 2006.
  2. Barnes J, Anderson LA, Phillipson DJ. Herbal Medicines. London: Pharmaceutical Press. 2007;279-289.
  3. European Scientific Cooperative of Phytotherapy. Monographs on the Medicinal uses of plant drugs: Fascicules 1 and 2 (1996), Fascicules 3, 4 and 5 (1997), Fascicule 6 (1999). Exeter: European Scientific Cooperative of phytotherapy.
  4. Schilcher H, Kammerer S, Wegener T. Leitfaden Phytotherapie. Urban & Fischer Verlag/ Elsevier GmbH, München. 3rd Edition. 2007;151-152.
  5. European Scientific Cooperative of Phytotherapy. Allii sativi bulbus. Monographs on the Medicinal uses of plant drugs. 2nd Edition. Thieme Verlag. 2003.
  6. European Scientific Cooperative of Phytotherapy. Monographs on the Medicinal uses of plant drugs: Fascicules 1 and 2 (1996), Fascicules 3, 4 and 5 (1997), Fascicule 6 (1999). Exeter: European Scientific Cooperative of phytotherapy.
  7. Bradley P. British Herbal Compendium. Vol. 1 Bournemouth: British Herbal Medicine Association. 1992.
  8. British Pharmaceutical Codex 1949: London: Pharmaceutical Press. 1949.
  9. Barnes J, Anderson LA, Phillipson DJ. Herbal Medicines. 2nd ed. London: Pharmaceutical Press. 2002.
  10. WHO. Monograph on selected medicinal plants, Vol 1. Geneva: WHO. 1999.
  11. Fleischauer AT, Poole C, Arab L. Garlic consumption and cancer prevention: meta-analyses of colorectal and stomach cancers. Am J Clin Nutr 2000; 72:1047-1052.
  12. Kim JY, Kwon O. Garlic intake and cancer risk: an analysis using Food and Drug Adminstration's evidence-based review system for the scientific evaluation of health claims. Am J Clin Nutr 2009; 89:257-264.
  13. Satia JA, Littman A, Slatore CG, Galanko JA, White E. Associations of herbal and specialty supplements with lung and colorectal cancer risk in the VITamins and Lifestyle study. Cancer Epidemiol Biomarkers Prev 2009; 18(5):1419-1429.
  14. Bianchini F, Vainio H. Allium vegetables and organosulfur compounds: do they help prevent cancer? Envir Health Persp 2001; 109(9):893-902.
  15. Fulder S. Garlic and the prevention of cardiovascular disease. Cardil Pract 1989; 7:30-35.
  16. Nakagawa S, et al. Acute toxicity test of garlic extract. J Toxicol Sci 1984; 9:57-60.
  17. Papageorgiou C, et al. Allergic contact dermatitis to garlic (Allium sativum L.) Identification of the allergens: The role of mono-, di-, and trisulfides present in garlic. Arch Dermatol Res 1983; 275:229-234.
  18. Symposium on the chemistry, pharmacology and medicinal applications of garlic. Cardiol Pract 7, 1-15. 1989.
  19. Symposium on the chemistry, pharmacology and medicinal applications of garlic. Cardiol Pract 7, 1-15. 1989.
  20. Sunter WH. Warfarin and garlic. Pharm J 1991; 246:722.
  21. Izzo AA, Ernst E. Interactions between herbal medicines and prescribed drugs: a systematic review. Drugs 2009; 69(13):1777-1798.
  22. Berginc K, Trdan T, Trontelj J, Kristl A. HIV protease inhibitors: garlic supplements and first-pass intestinal metabolism impact on the therapeutic efficacy. Biopharm Drug Dispos 2010; 31:495-505.
  23. Tanaka S, Haruma K, Masaki K, Nagata S, Kitadai Y, Manabe N et al. Effects of aged garlic extract (AGE) on colorectal adenomas: a double-blinded study. Hiroshima J Med Sci 2004; 53(3-4):39-45.
  24. Tanaka S, Haruma K, Yoshihara M, Kajiyama G, Amagase H, et al. Aged garlic extract has potential suppressive effect on colorectal adenomas in humans. J Nutr 2006; 136:821S-825S.
  25. Li H, Li H-Q, Wang Y, Xu H-X, Fan W-T, Want M-L et al. An intervention study to prevent gastric cancer by micro-selenium and large dose of allitridum. Chinese Med J 2004; 117(8):1155-1160.
  26. Ishikawa H, Saeki T, Otani T, Suzuki T, Shimozuma K, Nishino H et al. Aged garlic extract prevents a decline of NK cell number and activity in patients with advanced cancer. J Nutr 2006; 136:816S-823S.
  27. You WC, Brown LM, Zhang L, Jin M-L, Chang Y-S, et al. Randomized double-blind factorial trial of three treatments to reduce the prevalence of precancerous gastric lesions. J Natl Cancer Inst 2006; 98:974-983.
  28. Cox MC, Low J, Lee J, Walshe J, Denduluri N, Berman A et al. Influence of garlic (Allium sativum) on the pharmacokinetics of docetaxel. Clin Cancer Res. 2006;12:4636-40.
  29. Markowitz JS, DeVane CL, Chavin KD, Taylor RM, Ruan Y, Donovan JL. Effects of garlic (Allium sativum L.) supplementation on cytochrome P450 2D6 and 3A4 activity in healthy volunteers. Clin Pharmacol Ther. 2003;74:170-177.
  30. Hajda J, Rentsch KM, Gubler C, Steinert H, Stieger B, Fattinger K. Garlic extract induces intestinal P-glycoprotein, but exhibits no effect on intestinal and hepatic CYP3A4 in humans. Eur J Pharm Sci. 2010;41:729-35.
  31. Ho BE, Shen DD, McCune JS, Bui T, Risler L, Yang Z et al. Effects of Garlic on Cytochromes P450 2C9- and 3A4-Mediated Drug Metabolism in Human Hepatocytes. Sci Pharm. 2010;78:473-81.
  32. Greenblatt DJ, Leigh-Pemberton RA, von Moltke LL. In vitro interactions of water-soluble garlic components with human cytochromes p450. J Nutr. 2006;136:806S-9S.
  33. Le Bon AM, Vernevaut MF, Guenot L, Kahane R, Auger J, Arnault I et al. Effects of garlic powders with varying alliin contents on hepatic drug metabolizing enzymes in rats. J Agric Food Chem. 2003;51:7617-23.
  34. Piscitelli SC, Burstein AH, Welden N, Gallicano KD, Falloon J. The effect of garlic supplements on the pharmacokinetics of saquinavir. Clin Infect Dis. 2002;34:234-38.
  35. Berginc K, Milisav I, Kristl A. Garlic flavonoids and organosulfur compounds: impact on the hepatic pharmacokinetics of saquinavir and darunavir. Drug Metab Pharmacokinet. 2010;25:521-30.
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