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Sports Health | Garlic Reduces Free Radical Damage

Garlic Reduces Free Radical Damage

Smoking and nonsmoking adults who take a supplement containing aged garlic may reduce free radical damage in the body, according to a new report in the Journal of Nutrition.1 Free radicals are highly reactive molecules, usually derived from oxygen, which can cause damage to many different tissues and organs. Elevated levels of free radicals have been associated with the development of several chronic diseases, including hardening of the arteries (atherosclerosis), heart disease, diabetes, liver disease, and cancer. Compounds that inhibit the formation of oxygen-derived free radicals are known as antioxidants. Like vitamin C and vitamin E, garlic appears to be a potent antioxidant that protects against free radical damage.

This preliminary study examined the effects of an aged garlic extract in ten smoking and ten nonsmoking adults. Smokers were studied separately, as they tend to have elevated levels of free radicals. All participants consumed 5 ml (one teaspoon) of the extract daily for two weeks. Blood and urine levels of a specific marker of free radical activity (8-iso-prostaglandin F2±) were measured before starting treatment, after two weeks of treatment, and two weeks after discontinuing the garlic extract.

The results of the study showed that following two weeks of supplementation with aged garlic, smokers had a 35% decline in blood levels of the free radical marker, while nonsmokers had a 29% reduction. The decrease in the urinary levels of this marker paralleled the changes in the blood. After discontinuing treatment for two weeks, the marker returned close to the initial levels in both smokers and nonsmokers. This suggests that the benefits of aged garlic probably only occur while one is actively taking it.

Beyond garlic’s antioxidant potential, it has many other known health benefits. Aged garlic has been shown to inhibit the development of atherosclerosis and to lower cholesterol.2 3 4 Additionally, some evidence indicates aged garlic may help stimulate the immune system,5 6 and test tube studies have shown that aged garlic has anticancer properties.7 8 It is unknown whether aged garlic has the same anticancer effects in humans.


1. Dillon SA, Lowe GM, Billington D, Rahman K. Dietary supplementation with aged garlic extract reduces plasma and urine concentrations of 8-isoprostaglandin F2± in smoking and nonsmoking men and women. J Nutr 2002;132:168–71.
2. Effendy JL, Simmons DL, Campbell GR, Cambell JH. The effect of aged garlic extract, ‘Kyolic’ on the development of experimental atherosclerosis. Atherosclerosis 1997;132:37–42.
3. Steiner M, Khan AH, Holbert D, Lin RI. A double-blind crossover study in moderately hypercholesterolemic men that compared the effect of aged garlic extract and placebo administration on blood lipids. Am J Clin Nutr 1996;64:866–70.
4. Lau BHS, Lam F, Wang-Cheng R. Effect of an odor-modified garlic preparation on blood lipids. Nutr Res 1987;7:139–49.
5. Lau BH, Yamasaki T, Gridley DS. Garlic compounds modulate macrophage and T-lymphocyte functions. Mol Biother 1991;3:103–7.
6. Kandil OM, Abdullah TH, Elakdi A. Garlic and the immune system in humans: its effect on natural killer cells. Fed Proc 1987;46:441.
7. Pinto JT, Qiao C, Xing J, et al. Effects of garlic thioallyl derivatives on growth, glutathione concentration and polyamine formation of human prostate carcinoma cells in culture. Am J Clin Nutr 1997;66:398–405.
8. Riggs DR, DeHaven JI, Lamm DL. Allium sativum (Garlic) treatment for murine transitional cell carcinoma. Cancer 1997;79:1987–94.

Darin Ingels, ND, MT (ASCP), received his bachelor’s degree from Purdue University and his Doctorate of Naturopathic Medicine from Bastyr University in Kenmore, WA. Dr. Ingels is the author of Garlic and Cholesterol: Everything You Need to Know (Prima, 1999) and Natural Treatments for High Cholesterol (Prima, 2000). He currently is in private practice in Westport, CT, where he specializes in environmental medicine and allergies. Dr. Ingels is a regular contributor to Healthnotes and Healthnotes Newswire.

Copyright © 2002 Healthnotes, Inc. All rights reserved. This material may not be published, broadcast, rewritten, or redistributed.

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The health information contained in this site is not intended as medical advice and should not be considered a substitute for appropriate medical care. Any products mentioned in studies cited in Healthnotes articles are not necessarily endorsed by Bastyr. As with any product, consult with a natural health practitioner to discuss what may be best for you.


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