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Vampires Beware: Does garlic boost the immune system?

By Meredith Garber

October 24, 2008


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Background: Garlic

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Garlic is not only a delicious vegetable used in cooking to flavor food, it also has claims that it can be good for you. Garlic is a part of the onion family Alliaceae, which also includes shallots, chives and leeks. Garlic has been used for a very long time for both medicinal and cooking purposes. One day, maybe garlic will replace apples when people think about what keeps the doctor away.  What are the claims made about the effectiveness of garlic? What are the mechanisms, rationale, and purposes of the active components of garlic? What is the evidence of these claims and who is presenting this information? All of these questions and more will be answered in the sections below as to whether or not garlic helps the immune system.


                      Garlic, raw

                      Garlic, raw

Nutritional value per 100 g (3.5 oz)

Energy 150 kcal   620 kJ

Carbohydrates                                33.06 g

- Sugars  1.00g

- Dietary fiber  2.1 g 

Fat                                                   0.5 g

Protein                                             6.36 g

- β-carotene  5 μg                            0%

Thiamin (Vit. B1)  0.2 mg                 15%

Riboflavin (Vit. B2)  0.11 mg           7%

Niacin (Vit. B3)  0.7 mg                   5%

Pantothenic acid (B5)  0.596 mg     12%

Vitamin B6  1.235 mg                      95%

Folate (Vit. B9)  3 μg                       1%

Vitamin C  31.2 mg                          52%

Calcium  181 mg                             18%

Iron  1.7 mg                                     14%

Magnesium  25 mg                          7%

Phosphorus  153 mg                       22%

Potassium  401 mg                         9%

Sodium  17 mg                                           1%

Zinc  1.16 mg                                  12%

Manganese 1.672 mg   

selenium 14.2 mcg       

(Percentages are relative to US

recommendations for adults.)

Source: USDA Nutrient database (Search raw garlic)




Garlic and the Immune System


What are the claims?


According to Disabled World, a website that helps those of the aging population cope with being disabled, garlic is claimed to be a beneficial supplement that helps the heart and immune systems with its antioxidant properties, and helps maintain healthy blood circulation (lower blood pressure and cholesterol) ( It contains many healthy vitamins and minerals, such as vitamins A and C, potassium, phosphorous, 75 different sulfur compounds, and a number of amino acids. The primary active ingredients in garlic are thought to be the sulfur containing compounds, one being allicin, which is produced when the garlic clove is crushed, bruised, or chopped. One of garlic’s most potent health benefits includes the ability to enhance the body’s immune cell activity. It is said to stimulate T-lymphocyte and macrophage cells, promote interleukin-1 levels, and support natural killer cells, which are all part of a healthy immune system. The consumption of 1–3 cloves per day is useful for immune support and as a preventive against diseases and infection ( However, the University of Maryland Medical center points out in their Alternative Medicine Herbal Medicine section that there are some studies that report no effect of allicin for killing bacteria (



What is the rationale of garlic helping the immune system?


Allicin is said to have antibiotic properties, meaning it can help to break down a bacterial cell wall and is a potent agent that helps the body to inhibit the ability of germs to grow and reproduce by promoting phagocytosis by white blood cells. Supposedly, 1 milligram of allicin from garlic has a potency of 15 standard units of penicillin ( Garlic also has antioxidant properties and vitamins, which help to destroy free radicals from the environment that damage cell walls and contribute to many disorders and decreased immune system response.


Diagram of a Macrophage engulfing bacteria (part of the immune system). Image from



What evidence is out there on the web?


Not many websites offered definitive evidence for their claims, and many listed benefits of garlic without citing research or studies. The University of Maryland Medical Center says that, “Garlic may help the immune system function more effectively during times of need such as in cancer. In a study of 50 patients with inoperable colorectal, liver, or pancreatic cancer, immune activity was improved after they were given aged garlic extract for 6 months” A website called the Analyst, which is a site where people can fill out a questionnaire to get a possible diagnosis based on their symptoms, mentions evidence for the benefits of garlic, such as a study that showed enhancement of natural killer cells against the AIDS virus. does point out that the garlic use should be used daily and over a long period of time for effects to take place






Literature and Studies in Favor of Garlic Helping the Immune System


Many compounds in garlic have been investigated to demonstrate their antiviral, anticancer, antibacterial and antifungal properties. Several studies have shown certain derivatives from garlic are a wide spectrum and can cause stimulation of cellular immunity, thereby improving the immune system.

A recent study done in 2005 by Ghazanfari, Hassan, and Khamesipour at Shahed University in Tehran, Iran, tested whether the active ingredients in garlic helped to enhance parasite engulfment and destruction by macrophages in mice. Eight to ten week old female mice were infected with Leishmania major, which causes Leishmaniasis. This is an infectious disease caused by intracellular protozoa and the disease ranges from a self-healing cutaneous leishmaniasis to a lethal visceral form with high mortality, depending on the immune response. Peeled garlic was mixed in a ratio of 1 g of garlic to 1 ml of distilled water, and then used as a stock solution. There were two groups of mice selected, with 20 mice per group. One group was injected once with 20 mg garlic/kg weight. Another group was injected with a smaller fraction of garlic extract. The other group was injected with an equal volume of PBS i.p. and used as a control. Afterward, the mice were injected with Leishmania. Peritoneal cells of five mice from each group were harvested after 3, 5, 7 and 14 days of treatment. At the end of the experiment, the mice were then killed and the macrophage numbers were counted.

        The results showed that the number macrophages isolated from the garlic-treated mice were significantly (P < 0.001) higher than those of control group on days 3, 5, 7 and 14 after treatment. Results also showed an increased number of parasites present inside macrophages of mice that were treated with garlic than those mice in control groups. This reduction of the infection demonstrated macrophage activation and parasite destruction in garlic extract groups. It may be suggested that mannose-binding lectin of garlic probably facilitates the attachment of parasite to macrophage (Ghazanfar et al. 2005). Parasite ingestion by garlic may be enhanced by protein alteration and probably increases in receptor expression in the macrophage cell membrane. Based on this data, it seems that garlic acts as significant help in boosting the immune system against Leishmania major through several possible mechanisms.

(Ghazanfari et al. 2005)



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        Another study to test the effectiveness of garlic in humans for helping the immune system was done in an impressive study by Peter Josling in 2001 to test the effectiveness of garlic in preventing colds and showed the beneficial effects of garlic in cold prevention and immune system improvement. This was a twelve-week, double-blind placebo controlled study. One hundred forty-six volunteers received one capsule daily of either an allicin-containing garlic supplement or a placebo. Using a diary with a five-point scale, (five being the healthiest to one showing full cold symptoms), the volunteers recorded any of their symptoms and infections. The final results showed that sixty-three percent of the placebo group developed longer lasting cold symptoms and infections than the active-treatment garlic group. The placebo group had sixty-five colds during the study while the active-treatment garlic group just had twenty-four colds. Of those in the active-treatment garlic group that did catch a cold, they recovered faster and their symptoms lasted an average of only 1.52 days, in contrast to the placebo groups 5.01 days. The active-treatment garlic group required only 4.63 days to recover in contrast to the placebo group’s 5.63 days. In addition, only two of the active-treatment garlic group participants had more than one cold, compared to sixteen placebo members that became re-infected. The results demonstrated the effectiveness of an allicin-containing supplement as a preventative measure from the common cold virus. The study clearly indicates garlic supplements improve the immune system with excellent antiviral activity (Joslin 2001).


An antioxidant research study was done by Pal et al. in 2006 on thirty-six Wistar rats to determine the hepatoprotective effects of garlic on isoniazed (INH) and rifampicin (RIF)-induced liver injury. The research was supported by the Indian Council of Medical Research because pulmonary tuberculosis is one of the most common and fatal infectious diseases in India. The first drugs used in tuberculosis chemotherapy, and also associated with hepatotoxicity, are INH and RIF. During this twenty-eight day study, the thirty-six Wistar rats were divided into four groups. The control group was (8 saline treated), INH + RIF group (8), garlic group (8), and INH + RIF + garlic group (12). A hepatotoxicity study was successfully produced in those Wistar rats who orally received 50mg/kg of INH + RIF daily. The hepatoprotective portion of the study was done by simultaneously administering 0.25g/kg daily of freshly prepared garlic homogenate to the twelve rats with INH + RIF induced liver injury. At the end of the twenty-eight day experiment, a biopsy of each rats liver tissue was sectioned, examined and analyzed twelve hours after their last oral treatments. This experimental animal model study concluded that freshly prepared garlic homogenate could prevent the oxidative injury induced by INH + RIF.


In a 2005 article by Stephen R. Davis, a Senior Hospital Scientist, he reported that in China, a safe and successful garlic derivative called allitridium was effectively used in treating invasive fungal and bacterial infections. Patients with invasive fungal diseases are reported to have poor immune functions. The allitridium caused a release of interferon-gamma and also enhanced natural killer cell activity, promoting cellular immunity. Adding this garlic derivative to existing antifungal intravenous treatment therapies demonstrated that it was immunostimulatory.


Numerous studies, employing various models, examining aged garlic extract 

(AGE) and its immunomodularity effects, were discussed in the 2001 article, by 

Kyo et al. In the immunoglobulin (IG)E-mediated allergic mouse model, the data suggested that AGE played a leading role in allergies, evidenced by reducing rat ear inflammation. AGE was also shown to be effective in the transplanted carcinoma rodent model. The study revealed the tumor bearing rats receiving AGE had increased natural killer and killer cell activities in their spleens. The results indicated that AGE has anti-carcinogenic properties, being able to suppress tumor cell growth by stimulating immunoresponder cells. The final study discussed was a psychological stress model. This model contained three groups of rats: a normal group, stress control group and an AGE group. The study measured spleen weight, number of spleen cells, and the number of   hemolytic plaque-forming cells (PFC) in all groups. The experiment utilized a   communication box, to administer to the rats either electrical shock or psychological stress, over a four day period. At the end of the four days spleen weight, the number of spleen cells, and the number of PFC were measured. Results showed AGE restored the anti-SRBC plaque-forming cells (PFC), and notably improved the decreases in the spleen weight, and the number of spleen cells.  These studies suggest garlic has the ability to stimulate immune functions.


Critiques of the Studies


        Overall, the studies showed a positive effect of garlic in helping to boost the immune system. Probably the best evidence is through the Josling experiment, since it was a well-conducted, double-blind, placebo controlled study done on humans. With these factors and the large amount of subjects used in the test, this would allow for statistical significance and helps to eliminate possible confounding variables. The Ghazanfari et al. experiment also showed statistical significance that garlic helped to increase the number of macrophage cells. All of the articles and studies proved their hypothesis to be correct. However, there may need to be more research done to rule out other factors that may have caused the boost to the immune system. Although, considering how recently the literature and studies were published, this also supports that the more current research is still showing the effectiveness of garlic in helping the immune system.


Side Effects of too much Garlic


Consuming too much garlic can result in halitosis, and the smell of garlic can be present in sweat, mucus, vaginal discharge and even earwax. If too much raw garlic is consumed, a stomachache can ensue. Also, if garlic is applied externally, a burning sensation of the skin may occur If someone consumes more than three raw cloves of garlic a day, it may cause gas, bloating, diarrhea, and sometimes fever in some people



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Conclusions and Recommendations


        Overall, it does seem that garlic offers a great deal of benefit to helping the immune system against colds, fungus, cancer and other diseases. There are various garlic products on the market, such as fresh garlic in your local grocery store or supplements that are available for purchase at drug stores or health food stores. These can be used to help you enjoy the proven and undiscovered benefits that garlic can provide. However, if you choose to take a garlic supplement, you must make sure that the manufacturer has standardized the product and that the compounds in the supplements are active. As was mentioned previously, it is recommended that any form of garlic should be consumed daily and over a long period of time for the effects to be substantial.









Davis, S. (2005). An overview of the antifungal properties of allicin and its breakdown products – the possibility of a safe and effective antifungal prophylactic. Mycoses, 48(2), 95-100.


Ghazanfari, T., Hassan, Z. M., Khamesipour, A., (2005). Enhancement of peritoneal macrophage phagocytic activity against Leishmania major by garlic (Allium Sativum) treatment. Journal of Ethnopharmacology, 103 (2006), 333–337.


Josling, P. (2001). Preventing the common cold with a garlic supplement: a double-blind, placebo-controlled study. Advances in Natural Therapy, 18(4), 189-193.


Kyo, E., Uda, N., Kasuga, S., Itakura, Y. (2001). Immunomodulatory effects of aged garlic extract. Journal of Nutrition, 131(3),1075S-9S.


Pal, R., Vaiphei, K., Sikander, A., et al. (2006). Effect of garlic on isoniazid and rifampicin-induced hepatic injury in rats. World Journal of Gastroenterology, 12(4), 636-639.




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