Garlic and Cancer

In ancient times, garlic was used for the treatment of cancer of the uterus (Hartwell, 1960; Essman, 1984; Doetsch, 1989; Konvicka, 1983). Numerous reports, including several important epidemiological studies, have entered the scientific literature ever since, asserting that garlic has a favourable effect of various forms of cancer. The following provides an overview of the current research and points of view concerning this very interesting special area of medicine.

Six decades ago, several statistical studies indicated that cancer occurs the least in those countries where garlic and onions are eaten regularly - for instance, in the French Provence, Italy, the Netherlands, the Balkans, Egypt, India, and China (Lackhovsky, 1932; Lorand, 1934; Caspari, 1936; Guntzel-Lingner, 1941; Yang et al., 1994b; Wang et al., 1985; Dausch & Nixon, 1990; Seelert, 1989; Harris, 1979; Dorant et al., 1994b). In a review article, Auler (1936) referred to the connection between nutrition and cancer, especially to the cancer growth-inhibiting effect of leek plants (Allium plants). The practising physicians of the time were very good observers, but almost nothing was known about the real background of this phenomenon. It was thought that the inhibitory action of garlic on putrefaction in the intestines, together with the secretion-stimulating effect, brought about detoxification and an increase in resistance.

Stimulation of gastric juice secretion and restoration of the intestinal flora, combined with the resulting prevention of gastrointestinal autointoxication, may help to remove at least one of the possible causes of cancer. Garlic may therefore be useful as a cancer preventative agent, and its application as an anticancer drug is based on this assumption (Stoger, 1967, 1968, 1970, 1976; Caldwell & Danzer, 1988; Anonym, 1980). More recently, this idea has again been pursued, not only in Europe, but also in the Third World countries, where the favourable effects of garlic for cancer are well known (Krishnamurthy & Sreenivasamurthy, 1956; Duris et al., 1981; Schimmer et al., 1994; Abdullah et al., 1988; Sagmeister, 1987). For instance, the consumption of black or green tea, as well as of garlic, is known to be a culinary practice which inhibits tumorigenesis in the lung, forestomach, and esophagus (Yang et al., 1993, 1994b).

The only known study in which garlic has been used to treat patients with advanced stages of cancer was conducted by Spivak (1962). A garlic juice preparation was administered in doses of 0.2-2mL intravenously or 1-5mL intramuscularly daily for 3-7 days. Of 35 patients with cancer at various sites (lung, cervix, stomach, lower lip, mammary gland, larynx, and leukemia), 26 showed positive treatment results of differing degrees, though complete healing was not achieved in any case. There is a single-case report, however, of a man whose pituitary tumour shrank by 50% during the 5 months in which he ate 5-7 grams fresh garlic daily. This was the first case ever reported of reduction of this type of tumour without chemotherapy or surgery. (Rainov & Burkert, 1993).

Epidemiological studies comparing cancer incidence with consumption levels

of individual or grouped foods are currently the most important evidence that garlic may significantly reduce the risk of cancer, especially cancers of the gastrointestinal tract. In nearly all the published epidemiological studies related to garlic clove consumption, the decreased cancer incidence associated with garlic consumption was statistically significant. Most studies did not distinguish between raw and cooked garlic.

Stomach cancer is the cancer most clearly associated with an effect by garlic consumption. This is true for both raw and cooked garlic (Mei et al., 1982; Buiatti et al., 1989). A particularly noteworthy study in China was a comparison between two countries in the same province, which have very different garlic-eating habits (Mei et al., 1982, Han, 1983). The incidence of stomach cancer in Cangshan County, where the average person consumes 20g fresh garlic daily, was only 8% of that in Qixia County, where less than 1g/day is eaten. Furthermore, the concentration of gastric nitrite was found to be only 23% as high in the Cangshan residents as in the Qixia residents, an effect associated with the killing of nitrate-reducing bacteria by thiosulfinates (allicin etc.) (Mei et al., 1982, 1985). The inhibitory effect of garlic on the carcinogenic nitroso compounds was further substantiated when the same investigators fed 5g chopped garlic plus proline and nitrate to volunteers and then measured urinary levels of nitrosoproline. The urinary levels did not increase at all, whereas major increases were found when the same individuals were fed the same diet without garlic (Mei et al., 1989).

Another study in China, involving 564 patients with stomach cancer and 1131 controls in an area of China with a high incidence of gastric cancer, revealed a significant reduction in gastric cancer risk with increased consumption of Allium vegetables (You et al., 1988, 1989). Subjects in the group of the highest quartile of intake (more than 64g/day) experienced only 40% of the cancer incidence of those in the lowest quartile (less than 32g/day).

Protective effects were also found for individual Allium foods: garlic, scallions, and Chinese chive, but not for onions.

A very important epidemiological (prospective cohort) study for Americans has recently been published in which the intake of 127 foods (including 44 vegetables and fruits) was determined in 41,387 women (ages 55-69) followed by a five-year monitoring of colon cancer incidence (Steinmetz et al., 1994). The most striking result of this "Iowa Women’s Health Study" was the finding that garlic was the only food which showed a statistically significant association with decreased colon cancer risk. For cancers anywhere in the colon, the modest consumption of one or more servings of garlic (fresh or powdered) per week resulted in a 35% lower risk, while a 50% lower risk was found for cancer of the distal colon. Although this study of 127 foods did not include onions, several other epidemiological studies have shown that onions and other Allium species are usually associated with decreased gastrointestinal cancer risk. Although the results have been less consistent than with garlic (Steinmetz & Potter, 1991, 1993; Haenszel et al., 1972; You et al., 1989; Cook-Mozaffari et al., 1979; Tajima & Tominaga, 1985; Shu et al., 1993; Tuyns et al., 1992; Graham et al., 1994; Levi et al., 1993a, 1993b).

Furthermore, no effect of onions or leeks has been associated with lung cancer risk (Dorant et al., 1994b). An excellent review of nearly all of the epidemiological cancer studies for the various Allium vegetables has been published recently (Dorant, 1994). Some of the garlic studies have also been reviewed (Dorant et al., 1993).

In a recent series of epidemiological studies from the Netherlands, no association was found between garlic supplement (pills) consumption and risk for stomach, colon, rectum, lung or breast cancers (Dorant, 1994; Dorant et al., 1994a, 1994b, 1995). However, these studies should be viewed with caution, since the composition of garlic supplements varies tremendously with both type and brand.

From the many publications that have just been reviewed, it is apparent that the anti-cancer effects of garlic are likely due, perhaps equally, to both allicin or allicin-derived compounds as well as to unidentified compounds not related to allicin. The following is a summary of the evidence for possible active compounds.

1. Epidemiological studies from six different countries have consistently shown that garlic consumption is associated with decreased risk of gastrointestinal cancer.
2. A major decrease in incidence of gastric cancer in China, particularly where large amounts of allicin-yielding fresh garlic are eaten, is associated with the antibiotic effects of garlic and its thiosulfinates (allicin) toward decreasing the amount of nitrate-reducing bacteria in the stomach and hence the amounts of carcinogenic nitrosamines formed (Mei et al., 1981, 1982,1985). Therefore, allicin does appear to have an important role in prevention of gastric cancer.
3. Animal studies have indicated the importance of allicin, since dietary fresh garlic, but not alliinase-inhibited garlic, greatly decreased breast cancer incidence in C₃H mice (Kroning, 1964). Furthermore, at similar doses of volatile sulfur compounds, both chopped garlic (1.8mg allicin/kg body weight) and steam-distilled garlic oil (2.3mk allicin-derived allyl sulfides/kg) similarly decreased liver tumour incidence in toads (El-Mofty et al., 1994).
4. A large number of animal studies with allicin-derived diallyl disulfide and diallyl sulfide, most using very large doses (100-200mg/kg) (with the exception of Reddy and coworkers (1993) who showed positive effects with 4mg diallyl disulfide/kg), have shown positive effects toward decreasing carcinogen-induced cancer. Although allicin itself has not been tested, these studies indicate that allicin-derived compounds have the ability to affect cancer incidence. Studies with allicin-derived compounds are important to understanding the cancer effects of fresh garlic, since diallyl disulfide and other allicin-derived compounds are known to produce the same metabolite, allyl mercaptan, in blood or liver as does allicin (Lawson & Wang, 1993; Egen-Schwind et al., 1992b). Interestingly, alliin, which would be abundant in cooked garlic, may also be metabolized in the liver to diallyl disulfide and then to allyl mercaptan (Egen-Schwind et al., 1992b; Pentz et al., 1991).
5. Evidence from animal studies that compounds in garlic other than allicin also have an important anticancer role comes from the many studies that have been conducted with commercial aged garlic (contains little allicin, no active alliinase, and only trace levels of allicin-derived compounds) fed to rats at 2-4% of the diet, which have shown a consistent decrease in carinogen-induced tumours and DNA adducts (Liu & Milner, 1990; Amagase & Milner, 1993; Lin et al., 1992, 1994). The effective compounds in this extract are not known. S-allylcysteine has been proposed as the possible active agent, but its activity as a pure compound and its content in the extract are far too small to account for a significant portion of the activity of the aged extract.

Further studies on determining the anti-cancer activity of garlic and its active compounds should ideally include human intervention trials with both fresh and cooked garlic and possible spray-dried (no alliin) garlic. Animal studies on the allyl sulfides or other garlic-derived compounds should be conducted with considerably lower doses than have been typically used. Studies on the allyl sulfides would benefit by the use of steam-distilled garlic oil, which contains a variety of allyl sulfides, including the abundant diallyl tri- and tetrasulfides, which are more reactive than the mono- or disulfides. Furthermore, studies with garlic fractions should use fractions of known composition, particularly with respect to total sulfur, y-glutamyl-S-alkenylcysteines, S-alkenylcysteines, alliin, fructans etc.

Stable allicin is produced by a natural substrate �?enzyme reaction and can be classified under EEC Directive 88/388 and US Federal Register Title 21, Section 101.22. It is a pale yellow to colourless liquid, occasionally turbid. It can also be freeze dried, without significant loss of activity, to produce pale yellow to white 2mm granules.

Recently the medical journal Antimicrobial Agents and Chemotherapy have confirmed the chemotherapeutic Effects of Garlic. In Israel Weizmann Institute of Science have uncovered a molecular mechanism, which may be the basis for some of garlic's therapeutic effects.

The researchers were able to study how garlic works at the molecular level thanks to their unique biotechnological procedure for producing large quantities of pure allicin, garlic's main biologically active component.

One study, appearing in the October issue of the American Society for Microbiology's Antimicrobial Agents and Chemotherapy, explains how allicin fights infection. This research supports the notion that garlic is an excellent, although smelly, natural antimicrobial drug that can disable an unusually wide variety of infectious organisms.

The second study, reported in Biochimica Biophysica Acta, may help clarify the role allicin plays in preventing heart disease and other disorders. In the studies, the scientists revealed and characterized a molecular mechanism by which allicin blocks certain groups of enzymes. Allicin, created when garlic cloves are crushed, protects the plant from soil parasites and fungi and is also responsible for garlic's pungent smell.

A natural weapon against infection, the research reported in Antimicrobial Agents and Chemotherapy revealed allicin disables dysentery-causing amoebas by blocking two groups of enzymes, cysteine proteinases and alcohol dehydrogenases. Cysteine proteinase enzymes are among the main culprits in infection, providing infectious organisms with the means to damage and invade tissues. Alcohol dehydrogenase enzymes play a major role in these harmful organisms' metabolism and survival.

Because these groups of enzymes are found in a wide variety of infectious organisms such as bacteria, fungi and viruses, this research provides a scientific basis for the notion that allicin is a broad-spectrum antimicrobial, capable of warding off different types of infections. "It has long been argued that garlic can fight a wide range of infections and now we have provided biochemical evidence for this claim," the authors write.

The role of allicin in warding off infection may be particularly valuable in light of the growing bacterial resistance to antibiotics. It is unlikely that bacteria would develop resistance to allicin because this would require modifying the very enzymes that make their activity possible.

Institute scientists found that allicin blocks the enzymes by reacting with one of their important components known as sulfhydryl (SH) groups, or thiols. This finding has important implications because sulfhydryl groups are also crucial components of some enzymes that participate in the synthesis of cholesterol. By reacting with and modifying the sulfhydryl groups in those enzymes, allicin may prevent the production of artery clogging cholesterol. "It has been suggested that garlic lowers the levels of harmful cholesterol, and our study provides a possible explanation for how this may occur," the authors write. "However, more research is necessary to establish what role allicin might play in preventing the clogging up of arteries."

Complicating the issue is the concern blocking sulfhydryl groups in proteins may sometimes be harmful because these groups are also present in enzymes involved in some of the body's vital processes.

However, unlike most bacteria, human tissue cells contain detoxifying molecules of a substance called glutathione, which helps maintain appropriate sulfhydryl levels. These glutathione molecules can reverse the anti-sulfhydryl effects of small amounts of allicin. Measuring antioxidant activity while reaction with sulfhydryl groups appears to explain most of allicin's activity, it has also been suggested allicin acts as an antioxidant. The study reported in BBA confirmed this antioxidant effect and for the first time provided its quantitative assessment.

Antioxidants gobble up harmful free radicals believed to contribute to tumor growth, atherosclerosis, ageing and other processes. Producing pure allicin in large quantities in nature, allicin is created when garlic cloves are cut into or crushed. The cutting or crushing causes two components of garlic, alliin and the enzyme alliinase, to interact.

The pure semi-synthetic allicin can be stored for months without losing its effectiveness. In contrast, the natural compound loses its beneficial properties within hours because it begins to react with garlic's other components as soon as the clove is crushed.

Nature identical allicin liquid and powder is only available from The Garlic Centre. Please email for details.