Garlic

Botanical name: Allium sativum

Parts used and where grown

Garlic has been used since time immemorial as a culinary spice and medicinal herb. Garlic has been cultivated in the Middle East for more than 5,000 years and has been an important part of Traditional Chinese Medicine. The region with the largest commercial garlic production is central California. China is also a supplier of commercial garlic. The bulb is used medicinally.

Garlic has been used in connection with the following conditions (refer to the individual health concern for complete information):

Science Ratings	Health Concerns
	Atherosclerosis Warts (topical application)
	BPH (Kastamonu Garlic) Breast-feeding support Colon cancer (reduces risk of stomach, oesophageal, and colon cancers) Common cold High blood pressure High cholesterol High triglycerides Intermittent claudication
	Athlete’s foot Chronic candidiasis Ear infections (recurrent) HIV support Infection Parasites Peptic ulcer Sickle cell anaemia
Reliable and relatively consistent scientific data showing a substantial health benefit. Contradictory, insufficient, or preliminary studies suggesting a health benefit or minimal health benefit. For a herb, supported by traditional use but minimal or no scientific evidence. For a supplement, little scientific support and/or minimal health benefit.

Historical or traditional use (may or may not be supported by scientific studies)

Garlic is mentioned in the Bible and the Talmud. Hippocrates, Galen, Pliny the Elder, and Dioscorides all mention the use of garlic for many conditions, including parasites, respiratory problems, poor digestion, and low energy. Its use in China was first mentioned in A.D. 510. Louis Pasteur studied the antibacterial action of garlic in 1858.

Active constituents

The sulphur compound allicin, produced by crushing or chewing fresh garlic or by taking powdered garlic products with allicin potential, in turn produces other sulphur compounds: ajoene, allyl sulfides, and vinyldithiins.¹ Aged garlic products lack allicin, but may have activity due to the presence of S-allylcysteine.

Many publications have shown that garlic supports the cardiovascular system. While earlier trials suggest it may mildly lower cholesterol and triglyceride levels in the blood,² ³ ⁴ more recent trials found garlic to have minimal success in lowering cholesterol and triglycerides.⁵ ⁶ ⁷ Garlic also inhibits platelet stickiness (aggregation) and increases fibrinolysis,⁸ which results in a slowing of blood coagulation. It is mildly antihypertensive⁹ and has antioxidant activity.¹⁰

Garlic’s cardiovascular protective effects were illustrated in a four-year clinical trial on people 50–80 years old with atherosclerosis.¹¹ It was found that consumption of 900 mg of a standardised garlic supplement reduced arterial plaque formation by 5–18%. The benefits were most notable in women.

In test tube studies garlic has been found to have antibacterial, antiviral, and antifungal activity.¹² However, these actions are less clear in humans and do not suggest that garlic is a substitute for antibiotics or antifungal medications.

Human population studies suggest that eating garlic regularly reduces the risk of oesophageal, stomach, and colon cancer.¹³ ¹⁴ This may be partly due to garlic’s ability to reduce the formation of carcinogenic compounds.

How much is usually taken?

People who wish to consume garlic and have no aversion to its odour can chew from one to two whole cloves of raw garlic daily. For those who prefer it with less odour, enteric-coated tablets or capsules with approximately 1.3% allin are available. Clinical trials have used 600–900 mg (delivering approximately 5,000–6,000 mcg of allicin potential) per day in two or three divided amounts.¹⁵ ¹⁶ Aged-garlic extracts have been studied in amounts ranging from 2.4–7.2 grams per day.

Are there any side effects or interactions?

Many people enjoy eating garlic. However, some people who are sensitive to it may experience heartburn and flatulence. Because of garlic’s anti-clotting properties, people taking anticoagulant drugs should check with their doctor before taking garlic.¹⁷ Those scheduled for surgery should inform their surgeon if they are taking garlic supplements. Garlic appears to be safe during pregnancy and breast-feeding. In fact, two studies have shown that babies like breast milk better from mothers who eat garlic.¹⁸ ¹⁹

Are there any drug interactions?
Certain medicines may interact with garlic. Refer to drug interactions for a list of those medicines.

References
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1. Koch HP, Lawson LD (eds). Garlic: The Science and Therapeutic Application of Allium sativaum L and Related Species, 2d ed. Baltimore: Williams and Wilkins, 1996, 62–4.

2. Warshafsky S, Kamer R, Sivak S. Effect of garlic on total serum cholesterol: A meta-analysis. Ann Int Med 1993;119:599–605.

3. Silagy C, Neil A. Garlic as a lipid-lowering agent—a meta-analysis. J R Coll Phys London 1994;28:39–45.

4. Neil HA, Silagy CA, Lancaster T, et al. Garlic powder in the treatment of moderate hyperlipidaemia: A controlled trial and a meta-analysis. J R Coll Phys 1996;30:329–34.

5. McCrindle BW, Helden E, Conner WT. Garlic extract therapy in children with hypercholesterolemia. Arch Pediatr Adolesc Med 1998;152:1089–94.

6. Isaacsohn JL, Moser M, Stein EA, et al. Garlic powder and plasma lipids and lipoproteins. Arch Intern Med 1998;158:1189–94.

7. Berthold HK, Sudhop T, von Bergmann K. Effect of a garlic oil preparation on serum lipoproteins and cholesterol metabolism. JAMA 1998;279:1900–2.

8. Legnani C, Frascaro M, Guazzaloca G, et al. Effects of a dried garlic preparation on fibrinolysis and platelet aggregation in healthy subjects. Arzneim-Forsch Drug Res 1993;43:119–22.

9. Silagy CA, Neil HA. A meta-analysis of the effect of garlic on blood pressure. J Hyperten 1994;12:463–8.

10. Kleijnen J, Knipschild P, Ter Riet G. Garlic, onion and cardiovascular risk factors: A review of the evidence from human experiments with emphasis on commercially available preparations. Br J Clin Pharmacol 1989;28:535–44.

11. Koscielny J, Klüendorf D, Latza R, et al. The antiatherosclerotic effect of Allium sativum. Atherosclerosis 1999;144:237–49.

12. Hughes BG, Lawson LD. Antimicrobial effects of Allium sativum L. (garlic), Allium ampeloprasum L. (elephant garlic) and Allium cepa L. (onion), garlic compounds and commercial garlic supplement products. Phytother Res 1991;5:154–8.

13. Dorant E, van den Brandt PA, Goldbohm RA, et al. Garlic and its significance for the prevention of cancer in humans: A critical review. Br J Cancer 1993;67:424–9.

14. Fleishauer AT, Poole C, Arab L. Garlic consumption and cancer prevention: meta-analyses of colorectal and stomach cancers. Am J Clin Nutr 2000;72:1047–52.

15. Brown DJ. Herbal Prescriptions for Better Health. Rocklin, CA: Prima Publishing, 1996, 97–109.

16. Blumenthal M, Busse WR, Goldberg A, et al. (eds). The Complete Commission E Monographs: Therapeutic Guide to Herbal Medicines. Boston, MA: Integrative Medicine Communications, 1998, 134.

17. Brown DJ. Herbal Prescriptions for Better Health. Rocklin, CA: Prima Publishing, 1996, 97–109.

18. Mennella JA, Beauchamp GK. Maternal diet alters the sensory qualities of human milk and the nursling’s behavior. Pediatr 1991;88:737–44.

19. Mennella JA, Beauchamp GK. The effects of repeated exposure to garlic-flavored milk on the nursling’s behavior. Pediatr Res 1993;34:805–8.

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The information presented in Healthnotes is for informational purposes only. It is based on scientific studies (human, animal, or in vitro), clinical experience, or traditional usage as cited in each article. The results reported may not necessarily occur in all individuals. For many of the conditions discussed, treatment with prescription or over the counter medication is also available. Consult your doctor, practitioner, and/or chemist for any health problem and before using any supplements or before making any changes in prescribed medications. Information expires March 2007.