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Heart Disease Prevention, The Science of Garlic


Today, garlic is one of the most researched plant medicines. By 1996, more than 1,800 scientific studies had investigated garlic’s medicinal properties.2 Through these studies, garlic has been verified as an important natural supplement in the treatment of many health problems.

Why is garlic so beneficial?

Garlic chemistry is very complex. It’s rich in many active components, including 75 different sulfur compounds. Allicin, the substance that gives garlic its characteristic odor (and to those who partake of its goodness —garlic breath) is the compound that’s most prized. Most garlic producers strive to grow garlic plants with a high allicin yield.3 Without allicin, garlic might not have any benefit at all.

However, as important as allicin is to garlic growers and harvesters alike, the concentration of allicin in an intact clove of garlic is astonishingly small. This is because allicin is protected in the clove by cell walls. It is only after the cell walls are crushed or cut that garlic cloves release their allicin.3

While allicin itself has beneficial health effects, its greatest strength is in what it yields. Once allicin is released, many compounds are formed. These compounds are responsible for most of garlic’s health benefits. 4 Allicin itself is highly unstable. In fact, allicin cannot be detected in the bloodstream or urine at any time after eating garlic.5

Allicin is also destroyed by stomach acid. Many commercial garlic products are enteric-coated. The tablets go through the stomach intact without dissolving. This delivers the garlic tablet to the small intestine, where the tablet dissolves and releases its allicin. From the small intestine, allicin’s many compounds are formed and then enter the bloodstream. This form of supplementation also avoids the development of garlic breath.5

Is it true that garlic is good for the heart?

Garlic has many beneficial properties that improve the health of the heart and circulation. These include:

Recently, there have been some reports in the news that discount garlic’s ability to lower cholesterol. Why is there such a difference in garlic research results?

Prior to 1995, studies consistently concluded garlic lowered cholesterol levels. However, since 1995, many clinical trials have concluded garlic has no effect in lowering cholesterol levels in the blood. Researchers, concerned about these findings decided to determine why this occurred.5

The researchers, under the direction of Dr. Larry D. Lawson, examined the garlic supplements used in the studies that found no beneficial effect. One such study published in The Journal of the American Medical Association in 1998, concluded that garlic had no effect on serum cholesterol.14

While allicin cannot be detected in blood or urine, it can be detected in the breath. Using the exact products previously studied (same lot numbers and year of manufacture), Dr. Lawson measured the JAMA study’s test product, a garlic oil. When Dr. Lawson tested study subject’s breath after taking the garlic oil, minimal allicin was detected.

However, when Dr. Lawson encapsulated the same oil in gelatin capsules and had study subjects swallow the capsules, the same oil produced three times as much allicin.5

A recent meta-analysis (a large review study of several other studies with statistical analysis) of clinical trials concluded the use of garlic to lower cholesterol was, at best, of questionable value. Most of the studies published after 1995 that concluded garlic had no effect on serum cholesterol used non-enteric-coated tablets.15

Dr. Lawson studied the tablets used in these trials and determined the tablets dissolved in the stomach. The allicin was released too early, was destroyed by stomach acid, and never reached the bloodstream. 5

Dr. Lawson concluded the trials used poor-quality products. He further concluded that when enteric coated tablets are manufactured using garlic containing high allicin potential, serum cholesterol lowering effect should be noted. He urged new clinical trials with such supplements.5

Controversy comparing the effectiveness of supplements made with fresh garlic and those made from aged garlic extract. Is there any way to determine which type of garlic supplement is the most effective?

Some manufacturers of garlic supplements believe allicin is not the effective compound in garlic. These companies manufacture aged-garlic extract (AGE) products. They have initiated, funded, and conducted many studies regarding the safety of garlic juice, garlic powder, and enteric-coated garlic tablets. The studies have compared these products to their AGE products. The studies frequently conclude fresh garlic and enteric-coated garlic are harmful to stomach lining and can cause ulcers.16,17 However, recently at the American Herbal Products Association’s International Garlic Symposium, several noted garlic researchers and experts disagreed with these findings. During a roundtable discussion, the consensus determined there have been no successful independent replications of the AGE studies. Furthermore, the roundtable concluded that several ethnic groups consume large amounts of raw garlic every day without any associated ill effects. There has never been a clinically noted association of garlic consumption and ulcer formation. And, finally, the scientists questioned the validity of the study results due to sponsor-associated bias.18

What evidence is there for the anticancer benefits of garlic?

Much research has examined garlic’s role in the inhibition and prevention of various types of cancer. Some of these studies have evolved from the observations that certain ethnic groups who eat a lot of garlic in their diet have a low incidence of certain types of cancers.19

In a recent meta-analysis, the authors concluded garlic was especially effective in preventing stomach and colon cancers.20-22

Are there any other scientifically documented health benefits to garlic?

Garlic is a powerful detoxifying agent that can protect against various liver toxins. In an experimental study, garlic protected against acetaminophen (Tylenol®)-induced liver toxicity.23 This means that individuals who are taking Tylenol® may find garlic is beneficial. Garlic can also kill harmful bacteria, fungi, and viruses.24-26

Is there a recommended daily dosage for allicin?

Based on a great deal of clinical research, a medically validated commercial garlic product should provide a daily dose of a total allicin potential of 4,000 micrograms (mcg). This dosage equates to roughly one to four cloves of fresh garlic.19 Be sure to read labels; demand products that deliver a guaranteed yield of allicin and are enteric-coated to prevent premature release in the stomach.


Garlic is indeed a unique plant. It has a long and colorful history as both food and medicine, and is highly valued as both. Scientific study has provided understanding of the many benefits of garlic as a supplement. And, most importantly, many loyal enthusiasts worldwide attest to healthier hearts and improved lives simply from using garlic supplements.


1. Riddle JM. Garlic’s history as a medicine. Presentation at the American Herbal Products Association International Garlic Symposium. July 31, 2001.

2. Garlic. In: Blumenthal M, ed. Herbal Medicine: Expanded Commission E Monographs. Austin, Tex: American Botanical Council; 2000:139-148.

3. Ellmore GS, Milano E, Feldberg RS. Navigating the clove: mapping bioactive compounds in garlic (Allium sativum). Presentation at the American Herbal Products Association International Garlic Symposium. July 31, 2001.

4. Robbers JE, Tyler VE. Garlic. In: Tyler’s Herbs of Choice. New York, NY: The Haworth Herbal Press; 1999:132-137

5. Lawson LD, Wang ZJ, Papadimitrou D. Allicin release under simulated gastrointestinal condition for garlic powder tablets employed in clinical trials on serum cholesterol. Planta Medicine. 2001;67:13-18.

6. Ho SE, Ide N, Lau BH. S-allyl cysteine reduces oxidant load in cells involved in the atherogenic process. Phytomedicine. 2001;8:39-46.

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8. Gadkari JV, Joshi VD. Effect of ingestion of raw garlic on serum cholesterol level, clotting time and fibrinolytic activity in normal subjects. Journal of Postgrad Medicine. 1991;37:128-131.

9. Orekhov AN, Grunwald J. Effects of garlic on atherosclerosis. Nutrition. 1997;13:656-663.

10. Silagy C, Neil garlic as a lipid lowering agent—a meta-analysis. Journal of R College Physicians Lond. 1994;28:39-45.

11. Morcos NC. Modulation of lipid profile by fish oil and garlic combination. Journal of National Medical Association. 1997;89:673-678.

12. Al-Qattan KK, Khan I, Alnaqeeg MA, Ali M. Thromboxane-B2, prostaglandin-E2 and hypertension in the rat 2-kidney 1-clip model: a possible mechanism of the garlic induced hypotension. Prostaglandins Leukot Essent Fatty Acids. 2001;64:5-10.

13. Qidwai W, Qureshi R, Hasan SN, Azam SL. Effect of dietary garlic (Allium Sativum) on the blood pressure in humans-a pilot study. Journal of Pakistan Medical Association. 2000;50:204-207.

14. Berthold HK, Sudhop T, von Bergmann K. Effect of a garlic oil preparation on serum lipoproteins and cholesterol metabolism: a randomized controlled trial. JAM 1998;279:1900-1902.

15. Stevinson C, Pittler MH, Ernst E. Garlic for treating hypercholesteremia: a meta-analysis of randomized clinical trials. Annual Intern Medicine. 2000;133:420-429.

16. Sumiyoshi H. New pharmacological activities of garlic and its constituents. Nippon Yakurigaku Zasshi. 1997;1:93-97.

17. Kasuga S, Uda N, Kyo E, Ushijima M, Morihara N, Itakura Y. Pharmacologic activities of aged garlic extract in comparison with other garlic preparations. Journal of Nutrition. 2001;131:1080-1084.

18. Amagase H, Block E, Bordia A, Lawson LD. The controversial issues surrounding allicin versus non-allicin containing products. Presentation at the American Herbal Products Association International Garlic Symposium. Aug. 1, 2001.

19. Reuter HD, Koch HP, Lawson LD. Anticancer effects. In: Koch HP, Lawson LD. Garlic: The Science and Therapeutic Application of Allium sativum and Related Species. Baltimore, Md: Williams & Wilkins; 1998:176-187.

20. Fleischauer AT, Arab L. Garlic and cancer: a critical review of the epidemiologic literature. Journal of Nutrition. 2001; 131:1032S-1041S.

21. Knowles LM, Milner J. Possible mechanism by which allyl sulfides suppress neoplastic cell proliferation. Journal of Nutrition. 2001;131:1061S-1066S.

22. Lamm DL, Riggs DR. Enhanced immunocompetence by garlic: role in bladder cancer and other malignancies. Journal of Nutrition. 2001;131:1067S-1070S.

23. Hu JJ, Yoo JS, Lin M, Wang EJ, Yang CS. Protective effects of diallyl sulfide on acetaminophen-induced toxicities. Food Chemistry Toxicology. 1996;34:963-969.

24. Guo NL, Lu DP, Woods GL, et al. Demonstration of the anti-viral activity of garlic extract against human cytomegalovirus in vitro. Chinese Medical Journal of (Engl). 1993;106:93-96.

25. O’Gara EA, Hill DJ, Maslin DJ. Activities of garlic oil, garlic powder, and their diallyl constituents against Helicobacter pylori. Applied Environmental Microbiology. 2000;66:2269-2273.

26. Ledezma E, Marcano K, Jorquera A, et al. Efficacy of ajone in the treatment of tinea pedis: a double blind and comparative study with terbinafine. Journal of American Acad Dermatology. 2000;43:829-832.

Decker Weiss

Author Decker Weiss is a licensed naturopathic medical doctor in the state of Arizona.

Red Heart


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Updated: Dec 21 2013