Medical Attributes of Allium sativum - Garlic

by Jarrod Buzalewski, Andrew Julian, and Konstantina Papathomas
Wilkes University, Wilkes-Barre, PA

May, 2009
Allium sativum, commonly known as garlic, is member of the Alliaceae, or onion family (Coppi et. al., 2006). The garlic plant can grow to three feet tall and has leaves that extend approximately to the middle of the stem (Foster & Duke, 2000). Thin and narrow green spathes, or leaf-like bracts, surround its white flowers, and are usually two to four inches long (Foster & Duke, 2000). In addition, garlic reproduces by forming bulbs (Foster & Duke, 2000).

Garlic originally evolved in the flat, unforested grasslands of Asia (Foster & Duke, 2000), but its evolution and survival has been greatly affected by humans.  A. sativum is not found in the wild, except when it escapes cultivation, after which it can be seen in fields and along roadsides (Foster & Duke, 2000). Although not native to the US, garlic can be found primarily in the northeast from Tennessee and Missouri northward to New York (Foster & Duke, 2000).  The USDA Plants Database reports that garlic is present throughout the eastern United States and Canada, while several sightings have also occurred in Nebraska, Kansas, Oklahoma, and California in recent years (NRCS, 2009).

The earliest use of garlic was noted in Ancient Egypt, where garlic was a main component of the daily diet, and taken similar to a daily vitamin. The assumed purpose of garlic supplementation for the working class was to enable increased strength and productivity. The Codex Ebers also prescribed A. sativum for ailments such as abnormal growths and circulatory problems (Rivlin, 2001).

The trend of using garlic as a source of productivity and strength continued with the Jewish slaves in Egypt during the second millennium B.C., who were constantly fed garlic in hopes of optimizing efficiency. Little evidence suggests religious significance in Jewish culture, but historic texts document garlic use to treat infections and parasites (Rivlin, 2001).

The ancient Greeks were similarly among the first users of garlic. The Greek army diet consisted of high levels of garlic to aid productivity and work capacity. Garlic was often used during the Greek Olympics. Hippocrates and Dioscorides also advocated garlic to treat pulmonary ailments and abdominal growths, for “cleaning out arteries,” and as a purgative agent (Rivlin, 2001).

Similar uses for garlic were seen in India and China, especially in treating diarrhea and worm infections. The Renaissance then created a boom in the use of plants for medicinal treatments by all social classes. Garlic was also used for other purposes, including the treatment of fevers, colds, headaches, ear infections, arthritis, and circulatory problems, and was occasionally used as a diuretic (Rivlin, 2001).  In modern culture, garlic supplements remain a natural means of combating heart disease, bacterial infections, and oxidative damage to somatic tissues (Altman, 2009).

The principal active components found in Allium sativum include allicin, diallyl disulfide (DADS), ajoene, and S-allylcysteine or “SAC” (Bannerjey & Maulik, 2002).  Allicin is a thiosulfinate compound found in the Alliaceae (Coppi et. al., 2006).  The production of allicin is unique to plants of the genus Allium. Upon application of mechanical stress to the bulb, activated enzymes are exuded from cellular vacuoles.  One enzyme is alliinase that acts on the precursor amino acid alliin to generate allicin or 2-propenyl 2-propene thiosulfinate (Axelsson et. al., 2005; Coppi et. al., 2006).

Allicin has been demonstrated to reduce in vivo and in vitro cases of atherosclerosis in clinical studies involving humans. In such studies, regression of LDL-cholesterol levels in subjects were observed, ranging from decreases of 11-26 percent, while elevated HDL-cholesterol was seen in nearly all cases (Bannerjey & Maulik, 2002). Although the exact mechanism is not fully understood, researchers hypothesize that the likely mode of action involves inhibition of several enzymes necessary for cholesterol and fatty acid synthesis in the liver, including fatty acid synthase and HMG CoA reductase (Liu & Yeh, 2001).  A secondary source for reduction in triglyceride and cholesterol levels is the potent ability of garlic supplements to enhance steroidal excretions (Chi et. al., 1982).

According to Axelsson et al. (2005), the thiosulfinate group of allicin interacts with sulfhydryl groups of cysteine residues, present in many biologically significant proteins, thus causing diverse physiological effects.  For example, in addition to the numerous healthful benefits of A. sativum, several studies of garlic extracts cite allicin as a stimulant, which acts similarly to the compound capsaicin (Axelsson et. al., 2005).  Axelsson et. al. (2005) reported a 30 percent average increase in intracellular calcium levels in cultured sensory neurons (in vitro) following exposure to purified allicin or garlic extract, indicative of an in vivo excitatory response.

Aside from the cardiovascular benefits of allicin and other garlic-derived thiosulfinate compounds, modern research points to allicin as an effective anti-inflammatory, anti-clotting, anti-malarial, and anti-hypertensive agent (Liu & Yeh, 2001; Coppi et. al., 2006). In addition, both allicin and another thiosulfinate from garlic, called ajoene, provide “broad-spectrum antimicrobial activity,” useful for antibiotic preparations (Fujino et. al., 1996).

Aggarwal et. al. (2008) point to allicin and a metabolite of allicin, known as diallyl disulfide (DADS), as potent inducers of apoptosis in specific cell lines, including Colo 320 DM colon cancer cells in humans.  Similar effects of DADS have been observed with regard to cell lines implicated in melanomas, glioblastomas, neuroblastomas, and breast cancers in studies of mice and rats (Aggarwal et. al., 2008).  Other chemicals extracted from garlic, such as diallyl trisulfide (DATS), have proven effective against prostrate cancers and other cell malignancies (Xiao & Singh, 2005). 

Garlic extract, prepared by storing slices of bulb in ethanol (15-20%) for more than 20 months, promotes the formation of S-allylcysteine (SAC), allixin, and other thiosulfinate compounds that have been implicated to reverse oxidative damage in lipids, proteins, and DNA (Amagase et. al., 2001).  Oxidative damage to such organic macromolecules has been suggested to play a key role in the development of cardiovascular disease, cancer, and old-age dementias (eg. Alzheimer’s disease), and arise from bouts of inflammation, infection, smoking, drug consumption, and radiation (Xiao & Singh, 2005).  Since thiosulfinate antioxidants remove toxins from the body and stimulate maturation of certain white blood cells (macrophages and lymphocytes), aged garlic preparations also contain hepatoprotective and immune-enhancing properties (Amagase et. al., 2001; Blank, 1990).

Despite the many positive medicinal effects of A. sativum, some adverse interactions may result from garlic ingestion. High concentrations of the oil extracts from the bulb may cause irritation of the stomach (Izzo, 2001). Although garlic supplements are relatively safe, drastic results may occur from interaction(s) with prescription medications.  When mixed with paracetamol, garlic greatly alters pharmacotherapeutic properties and therefore analgesic efficacy of the drug. When combined with warfarin, the warfarin concentration in the blood stream may decrease among other detrimental effects. In addition, when garlic is taken with chlorpropamide, the combination may lead to hypoglycemia. (Izzo, 2001).

As noted, garlic has been cultivated by many cultures for over 7000 years (Foster & Duke, 2000) for its both clinically proven and folk-based medicinal uses. Studies have shown Allium sativum to clearly be an antifungal, an antibacterial, and a diuretic agent, as well as an effective supplement for treating hypertension, arteriosclerosis, gastrointestinal ailments and cancer. Aside from these verified maladies, A. sativum has been traditionally used to combat a variety of other illnesses, including fevers, colds, headaches, and earaches, to name a few (Foster & Duke, 2000). During the past thirty years, this plant has been the focus of over 2500 studies testing its medicinal value, which have provided generally positive results (Foster & Duke, 2000). Thus, when taken with care and proper dosage, garlic has tremendous value in treating a diverse array of health problems.

LITERATURE CITED

Aggarwal, B.B., P. Anand, A.B. Kunnumakara, B.H. Kuzhuvelil, O.S. Lai, C. Sundaram, B. Sung & S.T. Tharakan. 2008. Cancer is a preventable disease that requires major lifestyle changes. Pharm. Res. 25 (9), 2097-2116.

Altman, L. 2009. Three Ancient Herbs with Modern Health Benefits. Retrieved May 5, 2009 from Bright Hub Website: http://www.brighthub.com/health/diet-nutrition/articles/27329.aspx

Amagase, H., Y. Itakura, S. Kasuga, H. Matsuura, & B.L. Petesch. 2001. Intake of Garlic and Its Bioactive Components. The Journal of Nutrition. 131 (3s), 955S-62S.

Axelsson, H.E., D.M. Bautista, A. Hinman, E.D. Hogestatt, P. Movahed, & O. Sterner. 2005. Pungent products from garlic activate the sensory ion channel TRPA1.  Pharmacology 102 (34), 12248-12252.

Bannerjey, S.K. & S.K. Maulik.  2002. Effect of garlic on cardiovascular disorders: a review. Nutrition Journal. 1, 1-14.

Blank, D. 1990.  The word on herbs - garlic. Health Now Magazine.

Block, E.  1985.  The chemistry of garlic and onions. Scientific American. 252, 114-119.

Borek, C.  2001.  Antioxidant health effects of aged garlic extract. The Journal of Nutrition. 131 (3s), 1010S-15S.

Borek, C.  2006.  Garlic reduces dementia and heart-disease risk. The Journal of Nutrition. 136, 810S-12S.

Chi, M.S., E.T. Koh, & T.J. Stewart.  1982. Effects of garlic on lipid metabolism in rats fed cholesterol or lard. The Journal of Nutrition. 112 (2), 241-48.

Coppi, A., M. Cabinian, D. Mirelman, & P. Sinnis. 2006. Antimalarial activity of allicin, a biologically active compound from garlic cloves. Antimicrobial Agents and Chemotherapy. 50 (5), 1731-37.

Foster, S., & J.A. Duke.  2000. A field guide to medicinal plants and herbs of eastern and central North America (2nd ed.). Boston: Houghton Mifflin Company.

Fujino, T., H. Fukuda, K. Ishikawa, N. Iwata, R. Naganawa, & A. Suzuki.  1996. Inhibition of microbial growth by ajoene, a sulfur-containing compound derived from garlic. Appl. Environ. Microbiol. 62 (11), 4238-4242.

Izzo, A.A.  2001.  Interactions between herbal medicines and prescribed drugs: a systematic review. Drugs. 61, 2163-175.

Liu, L. & Y.Y. Yeh.  2001. Cholesterol-lowering effect of garlic extracts and organosulfur compounds: human and animal studies. The Journal of Nutrition. 131 (3s), 989S-93S.

Natural Resources Conservation Service: Plants profile. (2009). Allium sativum L. Cultivated garlic. Retrieved May 5, 2009, from USDA/NRCS Web site: http://plants.usda.gov/java/nameSearch?keywordquery=allium+sativum&mode=sciname&submit.x=0&submit.y=0

Rivlin, R.S. 2001. Historical Perspective on the Use of Garlic. The Journal of Nutrition. 131 (3s), 951-54.

Xiao, D. & S.V. Singh. 2005. Diallyl trisulfide, a constituent of processed garlic, inactivates Akt to trigger mitochondrial translocation of BAD and caspase-mediated apoptosis in human prostate cancer cells. Carcinogenesis. 1-26.

This paper was developed as part of the BIO 368 - Medical Botany course offered at Wilkes University during the spring of 2009. Course instructor was Kenneth M. Klemow, Ph.D. (kenneth.klemow@wilkes.edu). The information contained herein is based on published sources, and is made available for academic purposes only. No warrantees, expressed or implied, are made about the medical usefulness or dangers associated with the plant species in question.

Return to Plant Summaries page

This page posted and maintained by Kenneth M. Klemow, Ph.D., Biology Department, Wilkes University, Wilkes-Barre, PA 18766. (570) 408-4758, kenneth.klemow@wilkes.edu.