by Bea Heller, DC, MS, QME

Garlic is a member of the lily family, closely related to onions and leeks, that originally came from central Asia and is now cultivated throughout the world. Garlic is a perennial that can grow two feet high or more. The most important part of this plant for medicinal purposes is the compound bulb.

Not all garlic products contain the same amount of active ingredients. As with many plant-based products, there is a fairly wide variation in the amount of allicin and other important ingredients in both fresh garlic and commercial products. The amount present depends on where the garlic is grown, as well as how the product is prepared. The wide variation in the quantity of active ingredients in garlic preparations may explain why there is some variability in how well the substances lower cholesterol, improve blood pressure, and fight infection in different people.

Fermentation may reduce the amount of active ingredients in garlic. Cooking garlic at very high temperatures may also destroy its active components. It is best to use standardized garlic products to ensure you are getting a specified concentration of allicin and other active substances.

Properties

Alliin is nonvolatile, odorless, sulfur-containing chemical derived from the amino acid cysteine. When garlic bulbs are crushed, alliin is converted by action of the enzyme alliinase into another compound called allicin. Under normal conditions, alliinase and alliin are separated from each other inside the garlic bulb. However, when the bulb is cut or crushed, the two compounds are brought together and allinase converts alliin to allicin. This takes about 10-15 minutes. Chop garlic and let it rest for maximum conversion. Allicin appears to be at least one of the primary active compounds that gives garlic its characteristic odor and many of its healing benefits. Allicin appears to have infection-fighting action as well as potential cardiovascular effects, including, possibly, the ability to lower blood pressure and cholesterol. Test-tube studies have shown that allicin has anti-cancer activities. Allicin is further broken down to a compound called ajoene, which may be the substance that inhibits blockage in blood vessels from clots and atherosclerosis.

Garlic also contains bioflavonoids, iron, zinc, copper, manganese, and calcium, as well as vitamins, essential oil, sulphur compounds and sulphur-related compounds, plus citral, geraniol, etc.

History

The ancient Egyptians, Greeks, Romans, Indians and Chinese used garlic as both food and medicine for thousands of years. The primary use of garlic was as a treatment for tumors, headaches, weakness and fatigue, wounds, sores and infections. It was regarded as a physically enhancing tonic, and was used by the first Olympic athletes as an energizer. Old inscriptions note that pyramid builders were allotted garlic rations to ward off evil spirits and disease. Gravediggers in early 18^th-century France drank a concoction of crushed garlic in wine; they believed it would protect them from getting the plague that killed many people in Europe. During both World War I and World War II, soldiers were given garlic to prevent gangrene.

Louis Pasteur first demonstrated the anti-bacterial properties of garlic in 1858 and later, Albert Schweitzer used garlic to treat amoebic dysentery. More recently, researchers have demonstrated that garlic helps protect against heart disease and cancer, and that it possesses remarkable antibiotic effects. Garlic juice and its constituents can slow or kill more than 60 fungi and 20 types of bacteria, including some of the most virulent known to man.

Uses

Garlic also has antioxidant properties. Antioxidants help scavenge free radicals ø particles that can damage cell membranes, interact with genetic material, and possibly contribute to the aging process and the development of a number of conditions, including heart disease and cancer. Free radicals occur naturally in the body, but environmental toxins (including ultraviolet light, radiation, cigarette smoking and air pollution) also can increase the number of these damaging particles. Antioxidants can neutralize free radicals and may reduce or even help prevent some of the damage they cause over time. In one study, garlic-treated animals got 75-percent fewer tumors than control animals not given garlic. In a similar experiment, garlic completely protected mice against esophageal cancer. In other animal research, sulfur compounds of garlic inhibited stomach and skin cancers.

Studies suggest fresh garlic and garlic supplements may prevent blood clots and destroy plaque. Blood clots and plaque block blood flow and contribute to the development of atherosclerosis. Garlic also may be beneficial for risk factors for heart disease, including high blood pressure, high cholesterol, and diabetes. An animal study suggests garlic may help lower homocysteine levels as well. Homocysteine, similar to cholesterol, may contribute to increasing amounts of blood clots and plaque in blood vessels.

Long hailed for its beneficial effects, a number of studies have found that garlic reduces elevated total cholesterol levels more effectively than placebo. However, the extent to which garlic lowered cholesterol in these studies was small, and study limitations make it somewhat difficult to draw any firm conclusions. More research with better-designed studies is needed in order to fully assess the safety and effectiveness of garlic, and to determine the most appropriate dose and form.

Studies suggest raw garlic may lower blood pressure. Similar to cholesterol, however, the drop in blood pressure caused by garlic is fairly small. For this reason, further research is necessary before it can be recommended routinely for people with high blood pressure. Although garlic is considered relatively safe and has a number of other potentially healthful benefits for the heart, monitor your patientsÕ blood pressure closely while they are taking garlic in supplement form.

A study of nearly 150 people supports the value of garlic for preventing and treating the common cold. In this study, people received either garlic supplements or placebo for 12 weeks during Òcold seasonÓ (between November and February). Those who received the garlic had significantly fewer colds than those who received placebo, and cold symptoms lasted a much shorter time in those receiving garlic compared to those receiving placebo.

Test-tube and animal studies suggest garlic may have some anti-cancer activity. Studies suggest people who have more raw or cooked garlic in their diet are less likely to develop certain types of cancer, particularly colon and stomach cancers. Dietary garlic also may offer some protection against the development of breast, prostate, and laryngeal cancers; however, these types of cancer have not been studied as extensively.

More research is needed to best understand whether dietary intake of garlic and other substances in the same family (such as onions, leeks, scallions, chives, and shallots) truly help prevent cancer. In addition, studies looking at garlic supplements (as opposed to dietary garlic) and cancer have been limited. Thus far, however, use of garlic supplements does not appear to reduce the risk of developing prostate, colon, stomach, lung, or breast cancer.

Numerous test-tube studies have demonstrated that garlic extract inhibits the growth of different species of bacteria, including Mycobacterium tuberculosis. However, very high concentrations of garlic extract were needed to slow down the growth of M. tuberculosis in these studies, so some experts are concerned that these levels may be toxic to people. While further research in people is needed, one animal study found that garlic oil (which is a higher concentration than the extract) also inhibited M. tuberculosis and reduced the tuberculosis lesions in the lungs of these animals. Some scientists speculate that a combination of garlic extract or garlic oil with anti-tuberculosis drugs eventually may prove effective against the disease.

Laboratory studies suggest large quantities of fresh, raw garlic may have antiparasitic properties against the roundworm, Ascaris lumbricoides, the most common type of intestinal parasite. This has not yet been tested in people

Most children with an ear infection known as otitis media experience pain. Often, eardrops with painkillers are prescribed to relieve this discomfort. A recent study compared this standard treatment to a combination herbal extract (also used as eardrops) containing garlic, as well as calendula, St. JohnÕs wort, and mullein flower. The herbal combination worked as well as the prescription eardrops. The number of children included in the study, however, was small.

Side-effects from garlic 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 also may cause the appearance of skin lesions. Other side-effects that have been reported by those taking garlic supplements include headache, fatigue, loss of appetite, muscle aches, dizziness described as vertigo (namely, the room spinning), and allergies such as an asthmatic reaction or contact dermatitis (skin rash).

Cautions

Garlic has blood-thinning properties, so people with bleeding disorders, such as hemophilia or platelet disorders, should not use garlic supplements or medicinal doses of garlic. This also is important to know if you are going to have surgery or deliver a baby. Too much garlic can increase your risk for bleeding during or after those procedures.

Garlic may exaggerate the activity of medications that inhibit the action of platelets in the body. Examples of such medications include indomethacin, dipyridamole, and aspirin. There also have been reports of a possible interaction between garlic and warfarin that could increase the risk of bleeding in people taking this blood-thinning medication. Therefore, when taking medications that may thin the blood, such as aspirin and warfarin, you should refrain from consuming large quantities of garlic, either fresh or commercially prepared.

When used with a class of medications for diabetes called sulfonylureas, garlic may lower blood sugar considerably. Medications from this class include chlorpropamide, glimepiride, and glyburide. When using garlic with these medications, blood sugars must be followed closely. Garlic also may reduce blood levels of protease inhibitors, a medication used to treat people with the human immunodeficiency virus (HIV), including indinavir, ritinavir, and saquinavir.

It is thought that garlic may behave similarly to a class of cholesterol-lowering medications called statins (such as atorvastatin, pravastatin, and lovastatin) and to a class of blood-pressure- lowering medications called ACE inhibitors (including enalapril, captopril, and lisinopril). It is not known, therefore, whether it is safe to take this supplement in large quantities with these medications. This possible interaction has never been tested in scientific studies.