Garlic has been used as both food and medicine for thousands of years, dating back to when the Egyptian pyramids were built. In early 18th-century France, gravediggers drank crushed garlic in wine believing it would protect them from the plague. During both World Wars I and II, soldiers were given garlic to prevent gangrene. It was also used as an antiseptic, applied to wounds to prevent infection.
Today garlic is used to help prevent heart disease, including atherosclerosis or hardening of the arteries (plaque buildup in the arteries that can block the flow of blood and may lead to heart attack or stroke), high cholesterol, high blood pressure, and to boost the immune system. Eating garlic regularly may also help protect against cancer.
Garlic is rich in antioxidants. In your body, harmful particles called free radicals build up as you age, and may contribute to heart disease, cancer, and Alzheimer's disease. Antioxidants like those found in garlic fight off free radicals, and may reduce or even help prevent some of the damage caused over time.
The conditions for which garlic is showing the most promise include:
Garlic is most often mentioned as an herb for heart disease and atherosclerosis (hardening of the arteries), but the evidence is mixed. Some studies do suggest that garlic may help prevent heart disease. It may slow down atherosclerosis and lower blood pressure a little, between 5% and 8%. Most of the studies on high blood pressure have used a specific formulation called Kwai. One study that lasted 4 years found that people who took 900 mg daily of standardized garlic powder slowed the development of atherosclerosis. Garlic also seems to act as a blood-thinner, which may help prevent heart attacks and strokes.
Earlier studies found that garlic lowered high cholesterol, but almost all recent studies that are high quality have found that garlic didn't lower cholesterol.
Some early evidence suggests garlic may help prevent colds. In one study, people took either garlic supplements or placebo for 12 weeks during "cold season" between November and February. Those who took garlic had fewer colds than those who took placebo. Plus, when they did get a cold, the people taking garlic saw their symptoms go away faster than those who took placebo.
Garlic may strengthen the immune system, helping the body fight diseases such as cancer. In test tubes, garlic seems to kill cancer cells. And population studies -- ones that follow groups of people over time -- suggest that people who eat more raw or cooked garlic are less likely to get colon and stomach cancers and cancer of the esophagus. In fact, researchers who reviewed 7 studies found a 30% reduction in risk of colorectal cancer among people who ate a lot of raw or cooked garlic. Garlic supplements don't seem to have the same effect.
Garlic is a perennial that originally came from central Asia, and is now grown throughout the world. It can grow 2 feet high or more. The compound bulb is the part used for medicine. Each bulb is made up of 4 - 20 cloves, and each clove weighs about 1 gram. Garlic supplements can either be made from fresh, dried, aged, or garlic oil, and each may have different effects on the body.
What's It Made Of?
Researchers once thought that a chemical called allicin was responsible for garlics benefits, as well as its distinctive smell. But there are other chemicals in garlic, including some sulfur-containing compounds, that may help fight heart disease, and help prevent come cancers.
Garlic supplements are made from whole fresh garlic, dried, or freeze-dried garlic, garlic oil, and aged garlic extracts.
Not all garlic contains the same amount of active ingredients. It is important to read the label carefully. To get the most benefit, use standardized garlic products. Also, follow the directions of a health care provider who is experienced in herbal medicine.
How to Take It
Ask your doctor before giving garlic supplements to a child. Research hasn't yet found what an effective and safe dose might be.
Whole garlic clove (as a food supplement): 2 - 4 grams per day of fresh, minced garlic clove (each clove is approximately 1 gram)
Aged garlic extract: 600 - 1,200 mg, daily in divided doses
Tablets of freeze-dried garlic: 200 mg, 2 tablets 3 times daily, standardized to 1.3% alliin or 0.6% allicin. Products may also be found standardized to contain 10 - 12 mg/Gm alliin and 4,000 mcg of total allicin potential (TAP).
The use of herbs is a time-honored approach to strengthening the body and treating disease. Herbs, however, can trigger side effects and can interact with other herbs, supplements, or medications. For these reasons, herbs should be taken with care, under the supervision of a health care provider qualified in the field of botanical medicine.
Garlic is listed as Generally Recognized as Safe (GRAS) by the U.S. Food and Drug Administration.
Side effects include upset stomach, bloating, bad breath, body odor, and a stinging sensation on the skin from handling too much fresh or dried garlic. Handling garlic may also cause skin lesions. Other, more rare side effects that have been reported by those taking garlic supplements include headache, fatigue, loss of appetite, muscle aches, dizziness described as vertigo, and allergies such as an asthmatic reaction or skin rash.
Garlic acts like a blood-thinner. Too much garlic can increase your risk for bleeding during or after surgery. It may also interact with blood-thinning medications (see "Interactions").
People with ulcers or thyroid problems should ask their doctor before taking garlic.
Garlic may interact with a number of medications, including the ones listed below. To be safe, if you take an prescription medicines, ask your doctor before tkaing garlic supplements.
Isoniazid (Nydrazid) -- This medication is used to treat tuberculosis. Garlic may lower the amount of this medication that the body absorbs, menaing it might not work as well.
Birth control pills -- Garlic may make birth control pills less effective.
Cyclosporine -- Garlic may interact with cyclosporine, a medication taken after organ transplant, and make it less effective.
Blood-thinning medications -- Garlic may make the actions of these medications stronger, increasing the risk of bleeding. Blood-thinners include warfarin (Coumadin), clopidogrel (Plavix), and aspirin.
Medications for HIV/AIDS -- Garlic may lower blood levels of protease inhibitors, medications used to treat people with HIV. Protease inhibitors include:
Nonsteroidal anti-inflammatory drugs (NSAIDs) -- Both NSAIDs and garlic may increase the risk of bleeding. NSAIDs include ibuprofen (Advil, Motrin) and naproxen (Aleve) as well as prescription medications.
Ackermann RT, Mulrow CD, Ramirez G, Gardner CD, Morbidoni L, Lawrence VA. Garlic shows promise for improving some cardiovascular risk factors. Arch Intern Med. 2001;161:813-824.
Alder R, Lookinland S, Berry JA, et al. A systematic review of the effectiveness of garlic as an anti-hyperlipidemic agent. J Am Acad Nurse Pract. 2003;15(3):120-129.
Ang-Lee MK, Moss J, Yuan C-S. Herbal medicines and perioperative care [review]. JAMA. 2001;286(2):208-216.
Ashraf R, Aamir K, Shaikh AR, Ahmed T. Effects of garlic on dyslipidemia in patients with type 2 diabetes mellitus. J Ayub Med Coll Abbottabad. 2005;17(3):60-4.
Berthold HK, Sudhop T. Galic preparation for prevention of atherosclerosis. Curr Opin Lipidol. 1998;9(6):565-569.
Berthold HK, Sudhop T, von Bergmann K. Effect of a garlic oil preparation on serum lipoproteins and cholesterol metabolism. JAMA. 1998;279.
Borrelli F, Capasso R, Izzo AA. Garlic (Allium sativum L.): adverse effects and drug interactions in humans. Mol Nutr Food Res. 2007;51(11):1386-97.
Caron MF, White CM. Evaluation of the antihyperlipidemic properties of dietary supplements. Pharmacotherapy. 2001;21(4):481-487.
Dillon SA, Burmi RS, Lowe GM, et al. Antioxidant properties of aged garlic extract: an in vitro study incorporating human low density lipoprotein. Life Sci. 2003;72(14):1583-1594.
Dorant E, van den Brandt PA, Goldbohm RA. A prospective cohort study on the relationship between onion and leek consumption, garlic supplement use and the risk of colorectal carcinoma in The Netherlands. Carcinogenesis. 1996;17(3):477-484.
Dorant E, van den Brandt PA, Goldbohm RA, Hermus RJ, Sturmans F. Garlic and its significance for the prevention of caner in humans: a critical view. Br J Cancer. 1993;67(3):424-429.
Durak I, Yilmaz E, Devrim E, et al. Consumption of aqueous garlic extract leads to significant improvement in patients with benign prostate hyperplasia and prostate cancer. Nutr Res. 2003;23:199-204.
Fleischauer AT, Arab L. Garlic and cancer: a critical review of the epidemiologic literature. J Nutr. 2001;131:1032S-1040S.
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.
Fugh-Berman A. Herb-drug interactions [review]. Lancet. 2000;355:134-138.
Fugh-Berman A. Herbs and dietary supplements in the prevention and treatment of cardiovascular disease. Prev Cardiol. 2000;3:24-32.
Garlic supplements can impede HIV medication. J Am Coll Surg. 2002;194(2):251.
Gallicano K, Foster B, Choudhri S. Effect of short-term administration of garlic supplements on single-dose ritonavir pharmacokinetics in healthy volunteers. Br J Clin Pharmacol. 2003;55(2):199-202.
Gullett NP, Ruhul Amin AR, Bayraktar S, Pezzuto JM, Shin DM, Khuri FR, Aggarwal BB, Surh YJ, Kucuk O. Cancer prevention with natural compounds. Semin Oncol. 2010 Jun;37(3):258-81. Review.
Hassan ZM, Yaraee R, Zare N, et al. Immunomodulatory affect of R10 fraction of garlic extract on natural killer activity. Int Immunopharmacol. 2003;3(10-11):1483-1489.
Heck AM, DeWitt BA, Lukes AL. Potential interactions between alternative therapies and warfarin. Am J Health Syst Pharm. 2000;57(13):1221-1227.
Heron S, Yarnell E. Treating parasitic infections with botanical medicines. Altern Complement Ther. 1999;8:214-224.
Isaacsohn JL, Moser M, Stein EA, et al. Garlic powder and plasma lipids and lipoproteins: a multicenter, randomized, placebo-controlled trial. Arch Intern Med. 1998;158(11):1189-1194.
Izzo AA, Ernst E. Interactions between herbal medicines and prescribed drugs: a systematic review. Drugs. 2001;61(15):2163-2175.
James JS. Garlic reduces squinavir blood levels 50%; may affect other drugs. AIDS Treat News. 2001;375:2-3.
Josling P. Preventing the common cold with a garlic supplement: a double blind, placebo-controlled survey. Adv Ther. 2001;18(4):189-193.
Kannar D, Wattanapenpaiboon N, Savige GS, Wahlqvist ML. Hypocholesterolemic effect of an enteric coated garlic supplement. J Am Coll Nutr. 2001;20(3):225-231.
Kendler BS. Recent nutritional approaches to the prevention and therapy of cardiovascular disease. Prog Cardiovasc Nurs. 1997;12(3):3-23.
Koscielny J, Klubendorf D, Latza R, Schmitt R, Radtke H, Siegel G, Kiesewetter H. The antiatherosclerotic effect of Allium sativum. Atherosclerosis. 1999;144:237-249.
Levi F, Pasche C, La Vecchia C, Lucchini F, Franceschi S. Food groups and colorectal cancer risk. Br J Cancer. 1999;79(7-8):1283-1287.
Loy MH, Rivlin RS. Garlic and cardiovascular disease. Nutr Clin Care. 2000;3(3):146-151.
Mantle D, Lennard TW, Pickering AT. Therapeutic applications of medicinal plants in the treatment of breast cancer: a review of their pharmacology, efficacy and tolerability. Adverse Drug React Toxicol Rev. 2000;19(3):223-240.
Markowitz JS, Devane CL, Chavin KD, et al. Effects of garlic (Allium sativum L.) supplementation on cytochrome P450 2D6 and 3A4 activity in healthy volunteers. Clin Pharmacol Ther. 2003;74(2):170-177.
Mashour NH, Lin GI, Frishman WH. Herbal medicine for the treatment of cardiovascular disease. Arch Intern Med. 1998;158:22252234.
Miller LG. Herbal medicinals: selected clinical considerations focusing on known or potential drug-herb interactions [review]. Arch Intern Med. 1998;158:2200-2211.
Milner JA. A historical perspective on garlic and cancer. J Nutr. 2001;131(3s):1027S-1031S.
Munday JS, James KA, Fray LM, Kirkwood SW, Thompson KG. Daily supplementation with aged garlic extract, but not raw garlic, protects low density lipoprotein against in vitro oxidation. Atherosclerosis. 1999;143(2):399-404.
Ngo SN, Williams DB, Cobiac L, Head RJ. Does garlic reduce the risk of colorectal cancer? A systematic review. J Nutr. 2007;137(10):2264-9.
Nies LK, Cymbala AA, Kasten SL, et al. Complementary and alternative therapies for the management of dyslipidemia. Ann Pharmacother. 2006;40(11):1984-92.
O'Gara EA, Maslin DJ, Nevill AM, Hill DJ. The effect of simulated gastric environments on the anti-Helibacter activity of garlic oil. J Appl Microbiol. 2008; 104(5):1324-31.
Pinto JT, Rivlin RS. Antiproliferative effects of allium derivatives from garlic. J Nutr. 2001;131(3S):1058S-1060S.
Rahman K. Effects of garlic on platelet biochemistry and physiology. Mol Nutr Food Res. 2007;51(11):1335-44.
Rahman K. Historical perspective on garlic and cardiovascular disease. J Nutr. 2001;131(3s):977S-979S.
Ried K, Frank OR, Stocks NP. Aged garlic extract lowers blood pressure in patients with treated but uncontrolled hypertension: a randomised controlled trial. Maturitas. 2010 Oct;67(2):144-50.
Sarrell EM, Mandelberg A, Cohen HA. Efficacy of naturopathic extracts in the management of ear pain associated with acute otitis media. Arch Pediatr Adolesc Med. 2001;155:796-799.
Salih BA, Abasiyanik FM. Does regular garlic intake affect the prevalence of Helicobacter pylori in asymptomatic subjects? Saudi Med J. 2003;24(8):842-845.
Scharbert G, Kalb ML, Duris M, Marschalek C, Kozek-Langenecker SA. Garlic at dietary doses does not impair platelet function. Anesth Analg. 2007;105(5):1214-8.
Siegers CP, Steffen B, Robke A, Pentz R. The effects of garlic preparations against human tumor cell proliferation. Phytomedicine. 1999;6(1):7-11.
Silagy CA, Neil AW. A meta-analysis of the effect of garlic on blood pressure. J Hypertens. 1994;12:463-468.
Sobenin IA, Pryanishnikov VV, Kunnova LM, Rabinovich YA, Martirosyan DM, Orekhov AN. The effects of time-released garlic powder tablets on multifunctional cardiovascular risk in patients with coronary artery disease. Lipids Health Dis. 2010 Oct 19;9:119.
Spigelski D, Jones PJ. Efficacy of garlic supplementation in lowering serum cholesterol levels. Nutr Rev. 2001;59(7):236-241.
Steiner M, Khan AH, Holbert D, Lin RI. A double-blind crossover study in moderately hypercholesterolemic men that compared the effect of aged garlic extract and placebo administration on blood lipids. Am J Clin Nutr. 1996;64:866870.
Steinmetz KA, Kushi LH, Bostick RM, Folsom AR, Potter JD. Vegetables, fruit, and colon cancer in the Iowa Women's Health Study. Am J Epidemiol. 1994;139(1):1-15.
Stevinson C, Pittler MH, Ernst E. Garlic for treating hypercholesterolemia. Ann Intern Med. 2000;133(6):420-429.
Superko HR, Krauss RM. Garlic powder, effect on plasma lipids, postprandial lipemia, low-density lipoprotein particle size, high-density lipoprotein subclass distribution and lipoprotein(a). J Am Coll Cardiol. 2000;35(2):321-326.
Wang HX, NG TB. Natural products with hypoglycemic, hypotensive, hypocholesterolemic, antiatherosclerotic and antithrombotic activities. Life Sci. 1999;65(25):2663-2677.
Witte JS, Longnecker MP, Bird CL, Lee ER, Frankl HD, Haile RW. Relation of vegetable, fruit, and grain consumption to colorectal adenomatous polyps. Am J Epidemiol. 1996;144(11):1015-1025.
Yeh YY, Liu L. Cholesterol-lowering effect of garlic extracts and organosulfur compounds: human and animal studies. J Nutr. 2001;131(3s):989S-993S.
Review Date: 1/26/2011
Reviewed By: Steven D. Ehrlich, NMD, Solutions Acupuncture, a private practice specializing in complementary and alternative medicine, Phoenix, AZ. Review provided by VeriMed Healthcare Network.
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