VITAMINS AND DIETARY SUPPLEMENTS: GARLIC

This article provides basic information about garlic — uses, potential side effects and resources for more information. Garlic is the edible bulb from a plant in the lily family. It has been used as both a medicine and a spice for thousands of years.

Common Names — garlic

Latin Name — Allium sativum

· Garlic's most common uses as a dietary supplement are for high cholesterol, heart disease and high blood pressure.

· Garlic also is used to prevent certain types of cancer, including stomach and colon cancers.

How It Is Used

· Garlic cloves can be eaten raw or cooked. They also may be dried or powdered and used in tablets and capsules. Raw garlic cloves can be used to make oils and liquid extracts.

What the Science Says

· Some evidence indicates that taking garlic can slightly lower blood cholesterol levels; studies have shown positive effects for short-term (one to three months) use. However, a study funded by the National Center for Complementary and Alternative Medicine, a part of the National Institutes of Health, on the safety and effectiveness of three garlic preparations (fresh garlic, dried powdered garlic tablets and aged garlic extract tablets) for lowering blood cholesterol levels found no effect.

· Preliminary research suggests that taking garlic may slow the development of atherosclerosis (hardening of the arteries), a condition that can lead to heart disease or stroke.

· Evidence is mixed on whether taking garlic can slightly lower blood pressure.

· Some studies suggest consuming garlic as a regular part of the diet may lower the risk of certain cancers. However, no clinical trials have examined this.

· NCCAM is supporting studies looking at how garlic interacts with certain drugs and how it can thin blood.

Side Effects and Cautions

· Garlic appears to be safe for most adults.

· Side effects include breath and body odor, heartburn, upset stomach and allergic reactions. These side effects are more common with raw garlic.

· Garlic can thin the blood (reduce the ability of blood to clot) in a manner similar to aspirin. This effect may be a problem during or after surgery. Use garlic with caution if you are planning to have surgery or dental work, or if you have a bleeding disorder. A cautious approach is to avoid garlic in your diet or as a supplement for at least one week before surgery.

· Garlic has been found to interfere with the effectiveness of saquinavir, a drug used to treat HIV infection. Its effect on other drugs has not been well studied.

· Tell your health care providers about any complementary and alternative practices you use. Give them a full picture of what you do to manage your health. This will help ensure coordinated and safe care.

Sources

1. Gardner CD, Lawson LD, Block E, 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. 2007;167(4):346-353.

2. National Cancer Institute. Garlic and Cancer Prevention: Questions and Answers. National Cancer Institute Web site. Accessed at cancer.gov/newscenter/pressreleases/garlic on April 28, 2006.

3. Agency for Healthcare Research and Quality. Garlic: Effects on Cardiovascular Risks and Disease, Protective Effects Against Cancer, and Clinical Adverse Effects. Accessed at ahrq.gov/clinic/epcsums/garlicsum.htm on April 28, 2006.

4. Garlic. Natural Medicines Comprehensive Database Web site. Accessed April 28, 2006.

5. Garlic (Allium sativum L.). Natural Standard Database Web site. Accessed April 28, 2006.

6. Garlic. In: Blumenthal M, Goldberg A, Brinckman J, eds. Herbal Medicine: Expanded Commission E Monographs. Newton, MA: Lippincott Williams & Wilkins; 2000:139-148.

7. Milner JA. Garlic (Allium sativum). In: Coates P, Blackman M, Cragg G, et al., eds. Encyclopedia of Dietary Supplements. New York: NY: Marcel Dekker; 2005:229-240.