Garlic Health Benefits
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Whole books have been written about garlic, an herb affectionately
called "the stinking rose" in light of its numerous therapeutic
benefits. A member of the lily or Allium family, which also includes onions and leeks, garlic is rich in a variety of powerful sulfur-containing compounds including thiosulfinates (of which the best known compound is allicin), sulfoxides (among which the best known compound is alliin), and dithiins
(in which the most researched compound is ajoene). While these
compounds are responsible for garlic's characteristically pungent odor,
they are also the source of many of its health-promoting effects.
More recent research has identified additional sulfur-containing
compounds that are responsible for garlic's star status as a
health-supporting food. These sulfur compounds include 1,2-vinyldithiin
(1,2-DT), and thiacremonone. The hydrogen sulfide gas (H2S) that can be
made from garlic's sulfides has also been the subject of great research
interest. When produced and released from our red blood cells, this H2S
gas can help dilate our blood vessels and help keep our blood pressure
under control.
Finally, when thinking about the sulfur compounds in garlic, it
is important to remember that sulfur itself is a key part of our health.
Several research studies have noted that the average U.S. diet may be
deficient in sulfur, and that foods rich in sulfur may be especially
important for our health. In addition to all of the sulfur-related
compounds listed above, garlic is an excellent source of manganese and
vitamin B6, a very good source of vitamin C, and a good source of
selenium.
Cardiovascular Benefits
Most of the research on garlic and our cardiovascular system has been
conducted on garlic powder, garlic oil, or aged garlic extracts rather
than garlic in food form. But despite this research limitation, food
studies on garlic show this allium vegetable to have important
cardioprotective properties. Garlic is clearly able to lower our blood
triglycerides and total cholesterol, even though this reduction can be
moderate (5-15%).
But cholesterol and triglyceride reduction are by no means
garlic's most compelling benefits when it comes to cardioprotection.
Those top-level benefits clearly come in the form of blood cell and
blood vessel protection from inflammatory and oxidative stress. Damage
to blood vessel linings by highly reactive oxygen molecules is a key
factor for increasing our risk of cardiovascular problems, including
heart attack and atherosclerosis. Oxidative damage also leads to
unwanted inflammation, and it is this combination of unwanted
inflammation and oxidative stress that puts our blood vessels at risk of
unwanted plaque formation and clogging. Garlic unique set of
sulfur-containing compounds helps protect us against both
possibilities—oxidative stress and unwanted inflammation.
On the anti-inflammatory side of the equation, garlic's
1,2-vinyldithiin (1,2-DT) and thiacremonone are the compounds that have
been of special interest in recent research. Both compounds appear to
work by inhibiting the activity of inflammatory messenger molecules. In
the case of thiacremonone, it is the inflammatory transcription factor
called NFkappaB that gets inhibited. In the case of 1,2-DT, the exact
anti-inflammatory mechanisms are not yet clear, even though the release
of inflammatory messaging molecules like interleukin 6 (IL-6) and
interleukin 8 (IL-8) by macrophage cells has been shown to be reduced in
white adipose tissue by 1,2-DT. The combination of anti-inflammatory
and anti-oxidative stress compounds in garlic makes it a unique food for
cardiovascular support, especially in terms of chronic degenerative
cardiovascular conditions like atherosclerosis.
In addition to the ability of garlic to help prevent our blood
vessels from becoming blocked, this allium vegetable may also be able to
help prevent clots from forming inside of our blood vessels. This
cardiovascular protection has been linked to one particular disulfide in
garlic called ajoene. Ajoene has repeatedly been shown to have
anti-clotting properties. It can help prevent certain cells in our blood
(called platelets) from becoming too sticky, and by keeping this
stickiness in check, it lowers the risk of our platelets clumping
together and forming a clot.
Equally impressive about garlic is its ability to lower blood
pressure. Researchers have known for about 10 years that the allicin
made from alliin in garlic blocks the activity of angiotensin II. A
small piece of protein (peptide), angiotensin II helps our blood vessels
contract. (When they contract, our blood is forced to pass through a
smaller space, and the pressure is increased.) By blocking the activity
of angiotensin II, allicin form garlic is able to help prevent unwanted
contraction of our blood vessels and unwanted increases in blood
pressure.
More recently, however, researchers have found that garlic
supports our blood pressure in a second and totally different way.
Garlic is rich in sulfur-containing molecules called polysulfides. It
turns out that these polysulfides, once inside our red blood cells
(RBCs), can be further converted by our RBCs into a gas called hydrogen
sulfide (H2S). H2S helps control our blood pressure by triggering
dilation of our blood vessels. When the space inside our blood vessels
expands, our blood pressure gets reduced. (H2S is described as a
"gasotransmitter" and placed in the same category as nitric oxide (NO)
as a messaging molecule that can help expand and relax our blood vessel
walls.) Interestingly, our RBCs do not appear to use processed garlic
extracts in the same way that they use polysulfides in food-form garlic.
Garlic's numerous beneficial cardiovascular effects are due to
not only its sulfur compounds, but also to its vitamin C, vitamin B6,
selenium and manganese. Garlic is a very good source of vitamin C, the
body's primary antioxidant defender in all aqueous (water-soluble)
areas, such as the bloodstream, where it protects LDL cholesterol from
oxidation. Since it is the oxidized form of LDL cholesterol that
initiates damage to blood vessel walls, reducing levels of oxidizing
free radicals in the bloodstream can have a profound effect on
preventing cardiovascular disease.
Garlic's vitamin B6 helps prevent heart disease via another
mechanism: lowering levels of homocysteine. An intermediate product of
an important cellular biochemical process called the methylation cycle,
homocysteine can directly damage blood vessel walls.
The selenium in garlic can become an important part of our body's antioxidant system. A cofactor of glutathione peroxidase
(one of the body's most important internally produced antioxidant
enzymes), selenium also works with vitamin E in a number of vital
antioxidant systems.
Garlic is rich not only in selenium, but also in another trace
mineral, manganese, which also functions as a cofactor in a number of
other important antioxidant defense enzymes, for example, superoxide dismutase. Studies have found that in adults deficient in manganese, the level of HDL (the "good form" of cholesterol) is decreased.
Anti-Inflammatory Benefits Across Body Systems
Our cardiovascular system is not the only body system that may be
able to benefit from garlic's anti-inflammatory properties. There's
preliminary evidence (mostly from animal studies, and mostly based on
garlic extracts rather than whole food garlic) that our our
musculoskeletal system and respiratory system can also benefit from
anti-inflammatory compounds in garlic. Both the diallyl sulfide (DAS)
and thiacremonone in garlic have been shown to have anti-arthritic
properties. And in the case of allergic airway inflammation, aged garlic
extract has been show to improve inflammatory conditions (once again in
animal studies).
Even more preliminary is research evidence showing that some
inflammatory aspects of obesity may be altered by sulfur-containing
compounds in garlic. Specifically, there is one stage in development of
the body's fat cells (adipocytes) that appears to be closely related to
status of our inflammatory system. Fat cells cannot become fully
themselves unless they are able to progress from a preliminary stage
called "preadipocytes" to a final stage called "adipocytes." One of the
sulfur compounds in garlic (1,2,-vinyldithiin, or 1,2-DT) appears able
to lessen this conversion of preadipocytes into adipocytes, and the
impact of 1,2-DT appears to be inflammation-related. Even though very
preliminary, this research on 1,2-DT is exciting because obesity is
increasingly being understood as a disease characterized by chronic, low
level inflammation and our inflammatory status is precisely where
garlic's 1,2-DT has its apparent impact.
Antibacterial and Antiviral Benefits
From a medical history standpoint, the antibacterial and antiviral
properties of garlic are perhaps its most legendary feature. This allium
vegetable and its constituents have been studied not only for their
benefits in controlling infection by bacteria and viruses, but also
infection from other microbes including yeasts/fungi and worms. (One
particular disulfide in garlic, called ajoene, has been successfully
used to help prevent infections with the yeast Candida albicans.) Very
recent research has shown the ability of crushed fresh garlic to help
prevent infection by the bacterium Pseudomonas aeruginosa in burn
patients. Also of special interest has been the ability of garlic to
help in the treatment of bacterial infections that are difficult to
treat due to the presence of bacteria that have become resistant to
prescription antibiotics. However, most of the research on garlic as an
antibiotic has involved fresh garlic extracts or powdered garlic
products rather than fresh garlic in whole food form.
Overgrowth of the bacterium Helicobacter pylori in the
stomach—a key risk factor for stomach ulcer—has been another key area of
interest for researchers wanting to explore garlic's antibacterial
benefits. Results in this area, however, have been mixed and
inconclusive. While garlic may not be able to alter the course of
infection itself, there may still be health benefits from garlic in
helping to regulate the body's response to that infection.
Garlic and Iron Metabolism
Recent research has shown that garlic may be able to improve our
metabolism of iron. When iron is stored up in our cells, one of the key
passageways for it to be moved out of the cell and returned into
circulation involves a protein called ferroportin. Ferroportin is
protein that runs across the cell membrane, and it provides a bridge for
iron to cross over and leave the cell. Garlic may be able to increase
our body's production of ferroportin, and in this way, help keep iron in
circulation as it is needed.
