Garlic (Allium sativum)

Garlic (Allium sativum) is a species of bulbous flowering plant in the genus Allium. Its close relatives include the onion, shallot, leek, chive, Welsh onion, and Chinese onion. It is native to Central Asia and northeastern Iran and has long been a common seasoning worldwide, with a history of several thousand years of human consumption and use. Numerous cuneiform records show that garlic has been cultivated in Mesopotamia for at least 4,000 years. The use of garlic in China and Egypt also dates back thousands of years. Well-preserved garlic was found in the tomb of Tutankhamun (c. 1325 BC).
It was consumed by ancient Greek and Roman soldiers, sailors, and rural classes (Virgil, Eclogues ii. 11), and, according to Pliny the Elder (Natural History xix. 32), by the African peasantry. Garlic was placed by the ancient Greeks on the piles of stones at crossroads, as a supper for Hecate (Theophrastus, Characters, The Superstitious Man). Currently, China produces over 70% of the world's supply of garlic.

Garlic (Allium sativum)

Uses

Garlic is primarily used as a spice and to treat hyperlipidemia, hypertension, atherosclerosis, cancer, and infections.

Chemistry/Pharmacology

Garlic has a variety of bioactive compounds, including organosulfur compounds, saponins, phenolic compounds, and polysaccharides. The major active components of garlic are its organosulfur compounds, such as diallyl thiosulfonate (allicin), diallyl sulfide (DAS), diallyl disulfide (DADS), diallyl trisulfide (DATS), E/Z-ajoene, S-allyl-cysteine (SAC), and S-allyl-cysteine sulfoxide (alliin). In general, organosulfur compounds in raw garlic have higher digestibility than those in cooked garlic. In addition, saponins were found to be more stable in the cooking process. The total amount of saponin in purple garlic was almost 40 times higher than that in white garlic, and several saponin compounds were only found to exist in purple garlic, such as desgalactotigonin-rhamnose, proto-desgalactotigonin, proto-desgalactotigonin- rhamnose, voghieroside D1, sativoside B1-rhamnose, and sativoside R1. Moreover, garlic contained more than 20 phenolic compounds, with higher contents than many common vegetables. The main phenolic compound was β-resorcylic acid, followed by pyrogallol, gallic acid, rutin, protocatechuic acid, as well as quercetin. Furthermore, garlic polysaccharides were reported to contain 85% fructose, 14% glucose, and 1% galactose.
Processing can have a substantial effect on the chemical content of garlic because the volatile oil components are heat-sensitive and certain enzymes are acid-labile. The best measure of total activity of garlic is its ability to produce allicin, which in turn, results in the formation of other active constituents. Several oral garlic formulations are available, and clinical studies have evaluated a variety of the proposed claims.

Clinical Studies

Epidemiologic studies show an inverse correlation between garlic consumption and progression of cardiovascular disease. Garlic has been shown to inhibit enzymes involved in lipid synthesis, decrease platelet aggregation, prevent lipid peroxidation of oxidized erythrocytes and LDL, increase antioxidant status, and inhibit angiotension-converting enzyme. Probably one of the most profound effects observed is garlic's ability to reduce platelet aggregation.
Data on whether garlic preparations may lower blood pressure are also mixed, but other meta-analyses suggest reductions in cardiovascular risk factors due to antihyperlipidemic effects, reduced inflammatory biomarkers, and improved glucose levels. Garlic extract also improved endothelial biomarkers associated with cardiovascular risk in obese individuals. Data also suggest immunostimulatory effects and benefits in patients with hepatopulmonary syndrome.
Several studies have evaluated whether garlic products can have protective effects against various cancers. In a large, randomized intervention trial, long-term garlic supplementation was associated with reduced risk of gastric cancer mortality but not incidence. Preliminary studies suggest aged garlic extract may reduce number and size of subsequent colorectal adenomas in patients with a history of adenoma and improve natural killer cell number and activity. Garlic supplementation may also be associated with reduced risk of hematologic malignancies.

Biomechanical Mechanism

The intact cells of garlic contain an odorless, sulfur-containing amino acid derivative known as alliin. When the cells are crushed, alliin comes into contact with the enzyme alliinase located in neighboring cells and is converted to allicin. Allicin has antibacterial and antimicrobial activity but is highly odoriferous and unstable. It also has antiplatelet and antihyperlipidemic activities. Most authorities agree that the best measure of the total activity of garlic is its ability to produce allicin, which, in turn, results in the formation of other active constituents.
In patients with hyperlipidemia, garlic might lower cholesterol levels by acting as an HMG-CoA reductase inhibitor. For atherosclerosis, garlic is believed to reduce oxidative stress and low-density lipoprotein oxidation and have antithrombotic effects. It is also thought to reduce blood pressure by causing smooth muscle relaxation and vasodilation by activating the production of endothelium-derived relaxation factor.
Garlic may stimulate both humoral and cellular immunity, causing T-cell proliferation, restoring suppressed antibody responses, and stimulating macrophage cytotoxicity on tumor cells. It may increase selenium absorption with possible protection against tumorigenesis. In addition, garlic may protect against certain cancers by halting cell cycle progression and inducing apoptosis of cancer cells as well as by decreasing angiogenesis and influencing carcinogen metabolism.

Sources/Articles

Ackermann RT, et al. Garlic shows promise for improving some cardiovascular risk factors. Arch Intern Med 2001;161:813-24.
Adak, Manoranjan, and J. A. Teixeira. "Garlic [Allium sativum] and its beneficial effect on cardiovascular disease: a review." Int. J. Biomed. Pharmaceut. Sci 4 (2010): 1-20. http://www.globalsciencebooks.info/Online/GSBOnline/images/2010/IJBPS_4(1&2)/IJBPS_4(1)1-20o.pdf
Agarwal, Kailash C. "Therapeutic actions of garlic constituents." Medicinal research reviews 16, no. 1 (1996): 111-124. https://d1wqtxts1xzle7.cloudfront.net/54880308/THERAPEUTIC_ACTIONS_OF_GARLIC_CONSTITUENTS-with-cover-page-v2.pdf?Expires=1645129233&Signature=ExiHRBec6-zlq2l~HoJhLH9wOCJBok2HsQBu6P7Dpms1HGw52gJAEPmdiGMDxpiyFzxl4B3GkJHvQlmocxZ42DJaYAPUOKFv6sIdpHrxLrzUMaNQP58NE0twW5R135gRQldIRgk27yRqVlQdP~WE77K8aTrQ6iS6axhaX3EPef7CMnraDuwZ48HNZY-rbeHT92cRfXhw0RcM44x-MY-QQv8lRN~7v-JuPmO-ljEotDa7mXq31VIhmKd8QPvimEDp6MTPSCnrBtql7F-MSm4Pc1gv5ddiYEOMrYyXkWEZufiy98yCo09R3cSCJY16XDRk26kypKtx84GwjWK0pveeEQ__&Key-Pair-Id=APKAJLOHF5GGSLRBV4ZA
Amagase H, et al. Intake of garlic and its bioactive components. J Nutr 2001;131:955S-62S.
Atkin M, Laight D, Cummings MH. The effects of garlic extract upon endothelial function, vascular inflammation, oxidative stress and insulin resistance in adults with type 2 diabetes at high cardiovascular risk. A pilot double blind randomized placebo controlled trial. J Diabetes Complications. May-Jun 2016;30(4):723-727.
Banerjee, Sanjay K., and Subir K. Maulik. "Effect of garlic on cardiovascular disorders: a review." Nutrition journal 1, no. 1 (2002): 1-14. https://nutritionj.biomedcentral.com/articles/10.1186/1475-2891-1-4?crsi=662497082&cicada_org_src=healthwebmagazine.com&cicada_org_mdm=direct
Berthold HK, et al. Effect of a garlic oil preparation on serum lipoproteins and cholesterol metabolism: a randomized controlled trial. JAMA 1998;279:1900-2.
Block, Eric. "The chemistry of garlic and onions." Scientific american 252, no. 3 (1985): 114-121. https://www.researchgate.net/profile/Eric-Block-3/publication/19185535_The_Chemistry_of_Garlic_and_Onions/links/53d7f53f0cf2a19eee7fe7d3/The-Chemistry-of-Garlic-and-Onions.pdf
Chiavarini M, Minelli L, Fabiani R. Garlic consumption and colorectal cancer risk in man: a systematic review and meta-analysis. Public Health Nutr. Feb 2016;19(2):308-317.
Darooghegi Mofrad M, Milajerdi A, Koohdani F, et al. Garlic Supplementation Reduces Circulating C-reactive Protein, Tumor Necrosis Factor, and Interleukin-6 in Adults: A Systematic Review and Meta-analysis of Randomized Controlled Trials. J Nutr. Apr 1 2019;149(4):605-618.
De BK, Dutta D, Pal SK, Gangopadhyay S, Das Baksi S, Pani A. The role of garlic in hepatopulmonary syndrome: a randomized controlled trial. Can J Gastroenterol. 2010 Mar;24(3):183-8.
Dirsch VM, et al. Effect of allicin and ajoene, two compounds of garlic, on inducible nitric oxide synthase. Atherosclerosis 1998;139:333-9.
Galeone C, Pelucchi C, Levi F, et al. Onion and garlic use and human cancer. Am J Clin Nutr 2006;84: 1027-32.
Galeone C, Pelucchi C, Dal Maso L, et al. Allium vegetables intake and endometrial cancer risk. Public Health Nutr. Nov 6 2008:1-4.
Gardner CD, et al. Effect of Raw Garlic vs Commercial Garlic Supplements on Plasma Lipid Concentrations in Adults With Moderate Hypercholesterolemia: A Randomized Clinical Trial. Arch Intern Med. 2007 Feb 26;167(4):346-53.
Guercio V, Galeone C, Turati F, et al. Gastric cancer and allium vegetable intake: a critical review of the experimental and epidemiologic evidence. Nutr Cancer. 2014;66(5):757-73.
Herman-Antosiewicz A, Powolny AA, Singh SV. Molecular targets of cancer chemoprevention by garlic-derived organosulfides.Acta Pharmacol Sin. Sep 2007;28(9):1355-1364.
Hodge G, et al. Allium sativum (garlic) suppresses leukocyte inflammatory cytokine production in vitro: potential therapeutic use in the treatment of inflammatory bowel disease. Cytometry 2002;48:209-15.
Hirsch K, et al. Effect of purified allicin, the major ingredient in freshly crushed garlic, on cancer cell proliferation. Nutr Cancer 2000;38:245-54.
Hsing AW, Chokkalingam AP, Gao YT, et al. Allium vegetables and risk of prostate cancer: a population-based study. J Natl Cancer Inst. Nov 6 2002;94(21):1648-1651.
Iciek, Małgorzata, Inga Kwiecień, and Lidia Włodek. "Biological properties of garlic and garlic‐derived organosulfur compounds." Environmental and molecular mutagenesis 50, no. 3 (2009): 247-265.
https://d1wqtxts1xzle7.cloudfront.net/43372292/Biological_properties_of_garlic_and_garl20160304-7421-1lswom0-with-cover-page-v2.pdf?Expires=1645197124&Signature=U20aLzGwzAni3qQv0~4NyTpd4mw~a62VYEFyKacyHzA4BeLXlxulnoRPX-szxn4cDKHHRsiS8SKXjXUkIdnbicZ3G4bYFSEEudN67HkQ8xegKG0IoN0Yiv6kRLXKjD~3m5gzZryx6W4SBxvuvXqhfXC1Y7pDzq8siE9oGGvTILsWFBw8PnEhF02Eadyf5Qm8BoIgU7A40o6~Du2sJ8~nghG5OyTa-xC5A8rIonFXlJdVIVqJGTAS9bTC5IGeeJXxFiNEuskVUgc-0Y3wlhI5hiC2-ShOpQVaGox9w-drztHvfZR9EMRH-Ix7z6pck2KIoDdeh1odU64Lags5GcoGjg__&Key-Pair-Id=APKAJLOHF5GGSLRBV4ZA
Isaacsohn JL, et al. Garlic powder and plasma lipids and lipoproteins: a multicenter, randomized, placebo-controlled trial. Arch Inter Med 1998;158:1189-94.
Ishikawa H, Saeki T, Otani T, et al. Aged garlic extract prevents a decline of NK cell number and activity in patients with advanced cancer. J Nutr. Mar 2006;136(3 Suppl):816S-820S.
Kannar D, et al. Hypocholesterolemic effect of an enteric coated garlic supplement. J Am Coll Nutr 2001;20:225-31.
Kwak JS, Kim JY, Paek JE, et al. Garlic powder intake and cardiovascular risk factors: a meta-analysis of randomized controlled clinical trials. Nutr Res Pract. 2014 Dec;8(6):644-54.
Lawson, Larry D. "Garlic: a review of its medicinal effects and indicated active compounds." Blood 179 (1998): 62. https://bigcanoe.themountainsvoice.com/wp-content/uploads/2020/01/garlic-Study_lawson1998.pdf
Li WQ, Zhang JY, Ma JL, et al. Effects of Helicobacter pylori treatment and vitamin and garlic supplementation on gastric cancer incidence and mortality: follow-up of a randomized intervention trial. Bmj. Sep 11 2019;366:l5016.
Li Z, Ying X, Shan F, et al. The association of garlic with Helicobacter pylori infection and gastric cancer risk: A systematic review and meta-analysis. Helicobacter. Oct 2018;23(5):e12532.
Lissiman E, Bhasale AL, Cohen M. Garlic for the common cold. Cochrane Database Syst Rev. 2012 Mar 14;3:CD006206.
Matsumoto S, Nakanishi R, Li D, et al. Aged Garlic Extract Reduces Low Attenuation Plaque in Coronary Arteries of Patients with Metabolic Syndrome in a Prospective Randomized Double-Blind Study. J Nutr. Feb 2016;146(2):427s-432s.
Ngo SN, Williams DB, Cobiac L, et al. Does garlic reduce risk of colorectal cancer? A systematic review. J Nutr. Oct 2007;137(10):2264-2269.
Pedraza-Chaverri J, et al. Garlic prevents hypertension induced by chronic inhibition of nitric oxide synthesis. Life Sci 1998;62:71-7.
Powolny AA, Singh SV. Multitargeted prevention and therapy of cancer by diallyl trisulfide and related Allium vegetable-derived organosulfur compounds. Cancer Lett. Oct 8 2008;269(2):305-314.
Qureshi AA, et al. Suppression of avian hepatic lipid metabolism by solvent extracts of garlic: impact on serum lipids. J Nutr 1983;113:1746-55.
Rahman, Khalid, and Gordon M. Lowe. "Garlic and cardiovascular disease: a critical review." The Journal of nutrition 136, no. 3 (2006): 736S-740S. https://academic.oup.com/jn/article/136/3/736S/4664300
Ried K. Garlic Lowers Blood Pressure in Hypertensive Individuals, Regulates Serum Cholesterol, and Stimulates Immunity: An Updated Meta-analysis and Review. J Nutr. 2016 Feb;146(2):389S-96S.
Rohner A, Ried K, Sobenin IA, et al. A systematic review and metaanalysis on the effects of garlic preparations on blood pressure in individuals with hypertension. Am J Hypertens. Mar 2015;28(3):414-423.
Shabani E, Sayemiri K, Mohammadpour M. The effect of garlic on lipid profile and glucose parameters in diabetic patients: A systematic review and meta-analysis. Prim Care Diabetes. Feb 2019;13(1):28-42.
Silagy CA, et al. A meta-analysis of the effect of garlic on blood pressure. J Hypertension 1994;12:463-8.
Song K, Milner JA. The influence of heating on the anticancer properties of garlic. J Nutrition 2001;131:1054S-7S.
Stabler SN, Tejani AM, Huynh F, Fowkes C. Garlic for the prevention of cardiovascular morbidity and mortality in hypertensive patients. Cochrane Database Syst Rev. 2012 Aug 15;8:CD007653
Stevinson C, et al. Garlic for treating hypercholesterolemia: a meta-analysis of randomized clinical trials. Ann Intern Med 2000;133:420-9.
Sun YE, Wang W, Qin J. Anti-hyperlipidemia of garlic by reducing the level of total cholesterol and low-density lipoprotein: A meta-analysis. Medicine (Baltimore). May 2018;97(18):e0255.
Szulinska M, Kregielska-Narozna M, Swiatek J, et al. Garlic extract favorably modifies markers of endothelial function in obese patients -randomized double blind placebo-controlled nutritional intervention. Biomed Pharmacother. Jun 2018;102:792-797.
Taghizadeh M, Hamedifard Z, Jafarnejad S. Effect of garlic supplementation on serum C-reactive protein level: A systematic review and meta-analysis of randomized controlled trials. Phytother Res. Feb 2019;33(2):243-252.
Tanaka S, Haruma K, Yoshihara M, et al. Aged garlic extract has potential suppressive effect on colorectal adenomas in humans. J Nutr. Mar 2006;136(3 Suppl):821S-826S.
Tattelman, Ellen. "Health effects of garlic." American family physician 72, no. 1 (2005): 103-106. https://www.aafp.org/afp/2005/0701/p103.html
Watson CJ, Grando D, Fairley CK, et al. The effects of oral garlic on vaginal candida colony counts: a randomised placebo controlled double-blind trial. BJOG. 2014 Mar;121(4):498-506.
Yeh, Yu-Yan, and Lijuan Liu. "Cholesterol-lowering effect of garlic extracts and organosulfur compounds: human and animal studies." The journal of nutrition 131, no. 3 (2001): 989S-993S. https://academic.oup.com/jn/article/131/3/989S/4687064
Zhou X, Qian H, Zhang D, et al. Garlic intake and the risk of colorectal cancer: A meta-analysis. Medicine (Baltimore). Jan 2020;99(1):e18575.