Garlic: Stinking Rose or Magic Bullet?

 Author: Winston Craig, MPH, PhD, RD.


Garlic (Allium sativum), a member of the lily family, is possibly the most popular herb in world cuisines. It has been cultivated for millennia. While it originated in central Asia it is now cultivated worldwide. Garlic has been used throughout the centuries both for food and medicine. Garlic owes much of its popularity in Europe to the Benedictine monks who grew garlic in their monastery gardens. Garlic was thought to be a valuable remedy to prevent communicable diseases.

The Greek historian Herodotus reported that large amounts of garlic, radishes, and onions were consumed by construction workers of the Egyptian pyramids. He claimed that the large amounts of garlic were necessary to protect the builders from febrile illnesses. In the ancient Codex Ebers, an Egyptian medical papyrus, no less than 22 of the drug formulations contained garlic.

Garlic belongs to the genus Allium along with the leeks, onions, shallots, and chives. Allium plants are perennials and usually form underground bulbs. The garlic bulb contains a cluster of 5 or more secondary bulbs called cloves. The cloves are harvested and used either fresh, dried, or powdered. The cut cloves have a pungent odor and strong flavor, due to the presence of many sulfur compounds.

Much of the garlic eaten in the United States is grown in Gilroy, Northern California. About 80% of the garlic crop is used for various dehydrated garlic products, while the rest is sold as fresh garlic. Garlic can be used in an endless variety of soups, dips, salad dressings, sauces, entrees, and vegetable dishes.

Antimicrobial Action

Garlic has been the subject of hundreds of scientific studies. Garlic has a broad spectrum antibiotic activity inhibiting the growth of a variety of microorganisms, including bacteria such as Staphylococcus, Streptococcus, Salmonella, E. coli; molds and yeasts such as Candida albicans; influenza and herpes viruses; and parasites. Garlic can also kill Helicobacter pylori, the bacteria associated with peptic ulcers. Garlic was used in Africa by Albert Schweitzer for the treatment of amebic dysentery. Garlic has been used to treat a variety of respiratory conditions such as colds and flu symptoms, coughs, bronchitis, and sinus congestion.

Protection Against Heart Disease

Studies have shown that garlic effectively reduces the risk of a heart attacks and stroke. A regular use of garlic can lower blood cholesterol levels and possibly raise HDL cholesterol levels. An analysis of 40 clinical studies revealed that, on average, one-half to one clove of garlic per day can reduce elevated blood cholesterol levels by about 10 percent and blood triglyceride levels by about 13% of the initial value. Garlic also lowers blood pressure levels due to its vasodilator properties and may be useful for patients with mild hypertension. In addition, garlic inhibits the formation of blood clots. In a well-controlled clinical study in the elderly, high-dose garlic powder significantly reduced the growth of atherosclerotic plaque by almost 20 percent and even achieved a slight regression over a 4 year period. Garlic also has some ability to lower blood glucose levels, especially in patients with diabetes.

Each clove of garlic contains about 1 percent of alliin, which converts to allicin when the clove is crushed, cut, or chewed. Garlic contains a large number of health-promoting substances, but it is allicin which is essential for the antimicrobial, lipid-lowering, and anti-clotting properties of garlic. Allicin is transformed into a variety of sulfur compounds dependent upon the method of food preparation.

Different garlic preparations have various effects. The most important factor is the content of alliin. Various formulations may differ in terms of standardized alliin content by as much as 20-fold. Enteric-coated pills, which dissolve in the intestinal tract, cut down on odor problems and improve the absorption of allicin, the key ingredient. Garlic powders best represent the composition of fresh garlic cloves than any other processed garlic.

Aged garlic extract (Kyolic), which is prepared by storing sliced garlic in 15-20 percent alcohol for 20 months, has lower amounts of sulfur and lacks the active sulfur compound alliin. Clinical studies using aged garlic extract have been less conclusive than those with fresh garlic or garlic powder products. In some studies with aged garlic extract it took about 6 months to lower blood lipids while garlic cloves and standardized garlic powder showed significant decreases after 1-2 months.

Protection Against Cancer

Various studies show that garlic can reduce the development of a number of cancers including stomach, prostate and colon cancer. Risk of prostate cancer was found to be 44 percent lower in those using garlic two or more times per week. In China, persons with the highest intake of garlic, onions and other allium vegetables had a risk of stomach cancer that was 40 percent lower than those with the lowest intake. In the Iowa Woman’s Health Study, the highest consumption of garlic was associated with a 32 percent reduced risk of colon cancer.

Garlic is also reported to stimulate the immune system, even in AIDS patients. It can enhance the activity of the lymphocytes and macrophages that destroy cancer cells, and disrupt the metabolism of tumor cells. Garlic inhibits the formation of nitrosamines in the stomach and thereby reduces the risk of gastrointestinal cancer. More research is needed to actually determine the quantity of garlic needed to minimize cancer risk. Garlic contains other health promoting compounds such as fructans, flavonoids, phenolic acids, phytosterols, and saponins that protect against chronic diseases.


Garlic has a strong antimicrobial action. It can lower lipid levels, inhibit blood clots, and enhance the immune system. To maintain good health it is recommended that a person consume about one clove (4 grams of fresh garlic) a day. Some people are allergic to garlic and suffer gastrointestinal distress. Large amounts should be avoided since it may cause heartburn and stomach complaints.

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