General Description
Garlic is a perennial plant that is cultivated around the world
and used widely as a culinary herb. A member of the lily family
and closely related to onions and chives, garlic grows up to 2 feet
in height with a smooth, round stem surrounded at the base by tubular
sheathes from which grow long, flat, linear leaves. The stem is
topped by a rounded cluster of small, white flowers. The garlic
bulb (the usable portion of the plant) is made up of 4 to 15 cloves
encased in a papery sheath that may be tan or pink in color.
Health applications
History and traditional use
Garlic has a long, rich history of use dating back thousands of
years. An herb surrounded by legend, garlic is mentioned in the
Homeric epics, the Bible, and the Talmud. Thought to possess magical
powers, garlic was used extensively in charms and spells, and was
believed to protect against evil spirits, vampires, demons, witches,
and other beings. The herb was used for a variety of health purposes
throughout history. In an Egyptian medical text dating back to 1550
B.C., garlic was recommended as a remedy for 22 different conditions,
including headaches, parasites, and heart conditions.1
The ancient physicians Hippocrates, Galen, Dioscorides, and Pliny
the Elder mention the use of garlic for a variety of conditions
ranging from parasitic infestation to low energy levels. Garlic
is the main ingredient in Four Thieves Vinegar, a folk remedy used
in France since the early eighteenth century. According to legend,
four condemned criminals were recruited to bury the dead during
a plague that devastated Marseilles in 1721. The gravediggers themselves
never fell ill with the disease because they drank a mixture of
macerated garlic and wine. Garlic's antibacterial activity was observed
by Louis Pasteur in 1858, and it was used widely as an antiseptic
for prevention of gangrene during World Wars I and II.2
Chemical composition
Most of the health benefits of garlic are attributed to the sulfur-containing
compound allicin and its derivatives. The primary source of garlic's
pungent odor, allicin is produced when garlic is crushed or chewed
and the enzyme alliinase reacts with the compound alliin. Allicin,
in turn, may be converted into other sulfur compounds including
ajoene, allyl disulfides, and vinyldithiins. Garlic is also naturally
rich in selenium, an essential trace mineral with a variety of
important roles in the body.
Cardiovascular
health
Garlic has long been valued as a natural way to promote cardiovascular
health, and research appears to support this reputation. Evidence
from numerous studies indicates that garlic can help reduce high
blood pressure,3-6 cholesterol, 7-11
and triglyceride12-15 levels, all of which
are considered risk factors for heart disease. Although exactly
how garlic works to lower cholesterol levels is still under investigation,
preliminary studies on laboratory animals suggest that it inhibits
the synthesis of cholesterol in the liver.16,17
Garlic is also rich in antioxidants that can help protect LDL
from oxidative damage.18-21 Oxidized LDL is
a major contributor to atherosclerosis. In addition to their effects
on cholesterol and triglycerides, studies suggest that compounds
in garlic may promote circulation by inhibiting blood clotting.22-26
Cancer
The popular belief that garlic protects against the development
of certain cancers may have some merit. In case-control studies,
subjects with higher intakes of garlic had fewer incidences of
colon27-28 and prostate29
cancers than subjects who consumed little or no garlic. Garlic
and two of its components, diallyl sulfide and diallyl disulfide,
have demonstrated anticancer activity in laboratory studies, but
further study is needed to determine the efficacy of garlic for
reducing cancer risk in humans.
Antimicrobial
activity
Garlic has been used throughout history to fight infection, and
modern research has shown that compounds in garlic have antiviral,34,35
antibacterial,36-39 antifungal,39-42
and antiparasitic activity.43-44 Because it
is active against such a broad range of organisms, garlic may
be helpful in a variety of health conditions.
Dosage/toxicity
The desirable dosage of garlic may vary from person to person.
Lipid-lowering effect can be expected with a daily dose of 600
to 900 mg of powdered garlic delivering 3.6 to 5.4 percent allicin.45
This amount is approximately equal to 1 clove (4 grams) of fresh
garlic. For most people, garlic is nontoxic at this dosage. Large
doses (20 grams or more per day) may cause heartburn or other
gastrointestinal problems. Some people suffer allergic reactions
as well. The alliin content (and allicin potential) of different
commercial garlic supplements varies and should be stated on the
label. Because the enzyme that converts alliin into allicin is
inactivated by stomach acids, enteric coated tablets or other
delivery systems that break down in the small intestines are the
preferred supplemental forms. Due to garlic's anti-clotting activity,
people on anticoagulant medications should only take garlic supplements
under a physician's supervision. |
