Garlic (Allium sativum ) reigns as a powerful -- and pungent -- leader among herbal remedies. A close cousin of onions, leeks, and shallots, garlic has traditionally been used to fight off everything from colds and infections to vampires and evil spirits. It's also one of the most intensely studied herbs; over the last 20 years, more than a thousand papers have been written about the "stinking rose" and its relatives.
What is it good for?
Garlic is currently under scrutiny for its potential to reduce the risk of heart disease, cancer, and even food poisoning. Several human studies have found that a daily dose of fresh garlic or some garlic supplements can modestly reduce cholesterol levels, a major risk factor for heart disease.
Although a 6-month study of various forms of garlic, published in the Archives of Internal Medicine, found no beneficial effect among adults with moderately high cholesterol levels, an 8-week study of people who consumed 20 grams of raw garlic plus a tablespoon of lemon juice daily found a significant decrease in total cholesterol, LDL cholesterol, and fibrogen. The three control groups who consumed either 20 grams of raw garlic, a tablespoon of lemon juice, or neither lemon juice nor garlic did not see a significant decrease in those areas, according to the International Journal of Preventive Medicine.
Population studies have found people who regularly ate garlic had lower rates of colon, prostate, esophageal, pancreatic, breast and stomach cancers. A 5-year clinical trial with 5,000 Chinese men found that garlic and selenium supplements reduced the incidence of stomach cancer by 52 percent. Another trial in Japan found that garlic supplements reduced the incidence of non-cancerous colorectal tumors. Finally, some research suggests that adding a clove of fresh garlic to your burger may help protect you against unfriendly bacteria such as E. coli.
How does it work?
The sulfur compounds that give garlic its trademark odor are probably also responsible for its benefits. Crush a garlic clove and you start a chemical reaction that produces allicin, an antibacterial compound that has killed nasty stomach bugs in laboratory tests. Allicin and its byproducts might help protect the heart by lowering cholesterol levels and thinning the blood.
As for how garlic might help to fight cancer, the National Cancer Institute notes that its protective effects could come from its antibacterial properties or its ability to block the formation of cancer-causing substances, enhance DNA repair, or reduce the proliferation of cancerous cells.
How safe is it?
Garlic has an excellent safety record, but don't overdo it. Eating more than five cloves of garlic daily can cause upset stomach, flatulence, nausea, and heartburn, and some people are allergic to the herb. Also, because garlic extract may keep blood from clotting, you shouldn't use it if you're already taking drugs to thin your blood, such as Coumadin (Warfarin). People being treated for HIV disease should talk with their doctor before using garlic. It has been found to reduce the effectiveness of an anti-HIV drug called Fortovase/Invirase (Saquinavir). Be careful about using fresh garlic on your skin -- it can cause serious burns.
What's the best way to take it?
The best form of garlic is raw cloves. Since cooking partly destroys the ability of garlic to produce allicin, you have to eat garlic raw to get most of its benefits. But by cutting open a garlic clove and letting it sit for several minutes before cooking it, you can still get many of its benefits. In addition, many of the studies that showed a beneficial effect used garlic supplements that you'll find in pharmacies and health food stores. Some researchers recommend taking tablets that are enteric-coated; the coating allows the pills to pass through the stomach to the small intestine, where the allicin can be released in a useful form. Keep in mind that the government does not regulate herbal supplements, so quality and potency may vary from product to product. Also, if garlic does help fight cancer, scientists do not yet know how much is needed to lower cancer risk.
References
Jellin JM, Gregory P, Batz F, Hitchens K, et al. Pharmacist's Letter/Prescriber's Letter Natural Medicines Comprehensive Database. Stockton, CA: Therapeutic Research Faculty.
Aslani N. Effect of Garlic and Lemon Juice Mexture on Lipid Profile and Some Cardiovascular Risk Factors in People 30-60 Years Old with Moderate Hyperlipidaemia: A Randomized Clinical Trial. International Journal of Preventive Medicine.
Sunter WH. Warfarin and garlic. Pharm J;246:722.
Piscitelli SC, Burstein AH, Welden N, et al. Garlic supplements decrease saquinavir plasma concentrations. 8th Conference on Retroviruses and Opportunistic Infections, Chicago, IL; Abstract 743.
Rafaat M, Leung AK. Garlic burns. Pediatr Dermatol;17(6):475-476.
Hviid K, Alsbjorn B. "Burns" caused by local application of garlic. [Article in Danish] Ugeskr Laeger;;162(50):6583-4.
Eating Right: Getting Garlic's Goodness, Health, Time Health Media Inc.
National Center for Complementary and Alternative Medicine. Garlic.
National Cancer Institute. Garlic and cancer prevention: Questions and answers.
Gardner, CD, et al. Effect of raw garlic vs. commercial garlic supplements on plasma lipid concentrations in adults with moderate hypercholesterolemia: A randomized clinical trial. Archives of Internal Medicine; 167(4): 346-53.
Randomized double-blind factorial trial of three treatments to reduce the prevalence of precancerous gastric lesions. Journal of the National Cancer Institute; 98(14): 974-83.
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