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Other common
name(s): garlic clove, garlic powder, garlic oil, allium,
allyl sulfides, ajoene
Scientific/medical
name(s): Allium
sativum
Description
Garlic is a member of the lily family and is closely related
to onions, leeks, and chives. Extracts and oils made from garlic are
sometimes used as herbal remedies.
Overview
Garlic is currently under study for its ability to reduce
cancer risk. However, there is not enough evidence at this time to
support eating large amounts of garlic or taking garlic supplements for
cancer prevention. Garlic may have the potential to interfere with
anesthesia or other medicines. It is reasonable to include garlic as
part of a balanced diet, unless one has a particular health problem or
is taking medication that has been shown to be adversely affected by
garlic.
How is it promoted for use?
Garlic and garlic supplements are sometimes promoted to
prevent or treat cancer. Several compounds in garlic may have
anti-cancer properties, but compounds of one type in
particular—the allyl sulfur compounds—are said to
play a major role. These compounds reportedly help the body get rid of
cancer-causing chemicals and help cause cancer cells to die naturally,
a process called apoptosis. There have also been claims that garlic has
immune-boosting properties that may reduce cancer cell growth and help
the body fight off diseases such as colds or the flu. These claims are
currently being studied.
Proponents claim garlic can be used to treat bacterial, yeast,
fungal, and parasitic infections and can be used to treat high blood
sugar levels. They also say it has properties that may help stomach and
abdominal problems. Garlic has also been claimed to reduce risk of
heart disease, lower cholesterol, and reduce blood pressure.
What does it involve?
Garlic is a vegetable commonly used to enhance the flavor of
foods. Extracts of garlic are also sold as dietary supplements in
health food stores, drug stores, and over the Internet.
There is much debate about what form and amount of garlic to
use to influence health. Proponents disagree as to whether garlic is
more helpful when eaten either raw or cooked, or whether garlic
extracts, powders, and oils available in tablet form are more or less
effective.
Garlic is on the Commission E (Germany's regulatory agency for
herbs) list of approved herbs. They suggest a dosage of fresh garlic
equal to 4 grams per day (or about one large clove per day) to help
reduce heart disease risk.
What is the history behind it?
Garlic has been used in cooking throughout recorded history in
many cultures around the world, especially those in the Orient, Middle
East, and the Mediterranean. Garlic is believed to be one of the first
cultivated plants, with cultivation thought to have started about 5,000
years ago in the Middle East. Garlic has also been used medicinally for
thousands of years and continues to be popular today.
What is the evidence?
Several studies from around the world have found that people
who eat more garlic seem to have a lower risk of certain types of
cancer. In particular, large human studies that looked at diet and
cancer have suggested that people who eat more garlic have a lower risk
of stomach, prostate, mouth and throat, kidney, and colorectal cancer.
The effect on risk of breast, bladder, ovarian, and lung cancers is
less clear. As always in population-based studies, it is possible that
other factors may account for the differences in cancer risk. The few
human studies that have looked at garlic supplements have not found
them to be helpful against cancer.
Many laboratory studies done in cell cultures and animals
suggest garlic may help reduce tumor growth. Cell culture studies have
shown garlic can help cancer cells die off normally, a process called
apoptosis. Other studies in cell cultures have found that substances in
garlic seem to be able to act as antioxidants. Some studies have also
suggested that garlic can act against Helicobacter pylori,
a bacterium thought to be a major cause of stomach cancer. Studies in
laboratory animals have found garlic may help protect against cancer of
the colon, skin, liver, and breast, among others.
Although results of some observational studies are
encouraging, randomized clinical trials in which people assigned by
researchers to receive either garlic or an inactive control substance
provide more reliable information. Very few studies of this type have
studied garlic and cancer risk. In one recent study conducted in China,
where stomach cancer is quite common, aged garlic extract and
steam-distilled garlic oil did not prevent this disease.
While some research on garlic is promising, it is very hard to
determine the exact role a particular food may have against cancer. It
is even more difficult when the food in question is often used in small
amounts, as is garlic. A balanced diet that includes 5 or more servings
a day of fruits and vegetables along with foods from a variety of other
plant sources such as nuts, seeds, whole grain cereals, and beans is
likely to be more effective than eating one particular food in large
amounts.
Some studies suggest that garlic can lower blood cholesterol
levels, although a recent clinical study funded by the National Center
of Complementary and Alternative Medicine did not confirm any effect.
This California study compared raw garlic with aged garlic extract,
powdered garlic, and a placebo in nearly 200 randomly assigned
volunteers. The garlic was given in doses of 4 grams per day over 6
months. At the end of the study, there was no significant difference in
LDL ("bad") cholesterol among the 4 groups. Other studies suggest that
garlic makes blood less likely to form clots, which might help prevent
heart disease and stroke. However, there is no reliable direct clinical
evidence that garlic can actually prevent heart attacks or strokes.
Evidence on garlic and blood pressure is mixed.
While some research on garlic is promising, it is very hard to
determine the exact role a particular food may have against cancer. It
is even more difficult when the food in question is often used in small
amounts, as is garlic. A balanced diet that includes five or more
servings a day of fruits and vegetables along with foods from a variety
of other plant sources such as nuts, seeds, whole grain cereals, and
beans is likely to be more healthful than eating one particular food in
large amounts.
Are there any possible problems or
complications?
This product is sold as a
dietary supplement in the United States. Unlike drugs (which must be
tested before being allowed to be sold), the companies that make
supplements are not required to prove to the Food and Drug
Administration that their supplements are safe or effective, as long as
they don't claim the supplements can prevent, treat, or cure any
specific disease.
Some such products may not
contain the amount of the herb or substance that is written on the
label, and some may include other substances (contaminants). Actual
amounts per dose may vary between brands or even between different
batches of the same brand.
Most such
supplements have not been tested to find out if they interact with
medicines, foods, or other herbs and supplements. Even though some
reports of interactions and harmful effects may be published, full
studies of interactions and effects are not often available. Because of
these limitations, any information on ill effects and interactions
below should be considered incomplete.
Eating large amounts of garlic may lead to irritation of the
digestive tract, causing stomach pain, gas, and vomiting.
Some research suggests that garlic may increase the risk of
bleeding due to its anti-clotting properties. It should not be used by
people who will be having surgery soon, especially if they are given
blood thinners or if bleeding after surgery is a concern. People on
blood thinning medications, such as warfarin (Coumadin) or aspirin,
should consult with their doctor before taking garlic supplements.
Garlic seems to affect enzymes in the liver that help remove
certain drugs from the body. This may result in reduced levels of some
drugs in the body, which could be especially important in people
undergoing chemotherapy. This is currently under study, but people
thinking about taking garlic supplements should speak with their doctor
first.
Relying on this type of treatment alone and avoiding or
delaying conventional medical carefor cancer may have serious health
consequences.
Additional Resources
More information from your American Cancer
Society
The following information on complementary and alternative
therapies may also be helpful to you. These materials may be found on
our Web site (www.cancer.org)
or ordered from our toll-free number (1-800-ACS-2345).
References
American Heart Association. Phytochemicals and Cardiovascular
Disease. Accessed at:
www.americanheart.org/presenter.jhtml?identifier=4722 on June 10, 2008.
Blumenthal M, ed. The
Complete German Commission E Monographs: Therapeutic Guide to Herbal
Medicines. Austin, Tx: American Botanical Council; 1998.
Dorant E, van den Brandt PA, Goldbohm RA. Allium vegetable
consumption, garlic supplement intake, and female breast carcinoma
incidence. Breast Cancer
Res Treat. 1995;33:163-170.
Fleischauer AT, Arab L. Garlic and cancer: a critical review
of the epidemiologic literature.
J Nutr. 2001;131:1032S-1040S.
Gardner CD, Lawson LD, Block E, et al. Effect of raw garlic vs
commercial garlic supplements on plasma lipid concentrations in adults
with moderate hypercholesterolemia: a randomized clinical trial. Arch Intern Med.
2007;167:346-353.
Gonzalez CA, Pera G, Agudo A. et al. Fruit and vegetable
intake and the risk of stomach and oesophagus adenocarcinoma in the
European Prospective Investigation into Cancer and Nutrition
(EPIC-EURGAST).
International Journal of Cancer. 2006;118:2559-2566.
Hsing AW, Chokkalingam AP, Gao YT, et al. Allium vegetables
and risk of prostate cancer: a population-based study. J Natl Cancer Inst.
2002;94:1648-1651.
Meijerman I, Beijen JH, Schellens JH. Herb-drug interactions
in oncology: focus on mechanisms of induction. Oncologist.
2006;11:742-752.
Ngo SN, Williams DB, Cobiac L, Head RJ. Does garlic reduce
risk of colorectal cancer? A systematic review. J Nutr.
2007;137:2264-2269.
Memorial Sloan-Kettering Cancer Center. About herbs: Garlic.
2005. Accessed at: http://www.mskcc.org/mskcc/html/69230 cfm on June
103, 2008.
NCCAM. Herbs at a Glance: Garlic. Accessed at:
http://nccam.nih.gov/health/garlic/ on June 10, 2008.
PDRhealth. Garlic. Accessed at:
www.pdrhealth.com/drug_info/nmdrugprofiles/herbaldrugs/101190.shtmlon
June 10, 2008.
Riggs DR, DeHaven JI, Lamm DL. Allium sativum (garlic)
treatment for murine transitional cell carcinoma. Cancer.
1997;79:1987-1994.
Schulz M, Lahmann PH, Boeing H, et al. Fruit and vegetable
consumption and risk of epithelial ovarian cancer: the European
Prospective Investigation into Cancer and Nutrition. Cancer Epidemiology, Biomarkers
& Prevention. 2005;14:2531-2535.
Sundaram SG, Milner JA. Diallyl disulfide induces apoptosis of
human colon tumor cells. Carcinogenesis.
1996;17:669-673.
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;139:1-15.
Tanaka S, Haruma K, Yoshihara M, et al. Aged garlic extract
has potential suppressive effect on colorectal adenomas in humans. Journal of Nutrition. 2006;
136(3 Suppl):821S-826S.
You WC, Brown LM, Zhang L, et al. Randomized double-blind
factorial trial of three treatments to reduce the prevalence of
precancerous gastric lesions.
Journal of the National Cancer Institute. 2006;
98:974-983.
Note: This information may not cover
all possible claims, uses, actions, precautions, side effects or
interactions. It is not intended as medical advice, and should not be
relied upon as a substitute for consultation with your doctor, who is
familiar with your medical situation.
Last Medical Review: 11/01/2008
Last Revised: 11/01/2008
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