Garlic and its significance for the prevention of cancer in humans: a critical view

Abstract

Summary Recently published results of epidemiologic case-control studies in China and Italy on gastric carcinoma in relation to diet suggest that consuming garlic may reduce the risk of gastric cancer. Chemical constituents of garlic have been tested for their inhibiting effect on carcinogenesis, using in vitro and in vivo models. In most experiments inhibition of tumour growth was established using fresh garlic extract, garlic compounds or synthetically prepared analogs. In this review the strengths and weaknesses of the experiments are discussed and the outcomes are evaluated to assess the possible significance of garlic or garlic compounds for the prevention of cancer in humans. It is concluded that evidence from laboratory experiments and epidemiologic studies is presently not conclusive as to the preventive activity of garlic. However, the available evidence warrants further research into the possible role of garlic in the prevention of cancer in humans.Elimination of carcinogenic substances from the environment is the preferable method to prevent malignant tumour development. However, contact with carcinogenic substances is not always avoidable (Wattenberg, 1985;Weinstein, 1981). Therefore, chemoprevention, in which the occurrence of cancer is prevented by administration of inhibitory compounds, has received increased attention (Malone, 1989; Wattenberg, 1985).The relation between the use of allium vegetables, especially garlic (Allium sativum, a member of the genus Allium to which some 500 species belong), and its constituents, and the occurrence of cancer in humans is of particular interest in this respect. In a number of reviews on the effects of garlic on health, possible preventive effects on the development of cancer in humans have been mentioned. Fenwick and Hanley (1985) reviewed experimental studies designed to demonstrate any anticancer activity of garlic, together with the results of an epidemiological study in China in which death rates between two adjacent provinces were compared. In the latter study the highest gastric death rate had been found in the province with the lowest intake. The possible anticancer activity of garlic was illustrated in an earlier review of two studies reporting the inhibition of transplanted tumours in mice (Bolton et al., 1982). In a publication on new dietary anticarcinogens and the prevention of gastrointestinal cancer, diallylsulfide, a component of garlic, was identified as a suppressing agent in dimethylhydrazine (DMH)-induced colon and nitrosomethylbenzylamine (NMBA)-induced oesophageal cancer development in rats (Wargovich, 1988). Suggested inhibitory mechanisms were evaluated in a review of selected recent publications on the effects of garlic on tumour formation in experimental animals (Sumiyoshi & Wargovich, 1989). In an earlier review free radical scavenging activity, immune system modulation and direct cytotoxic effect on cancer cells were discussed (Abdullah et al., 1988 (Bertram et al., 1987;Malone, 1989; Wattenberg, 1985;1990 (Malone, 1989), in vitro ...

Dietary modifiers of carcinogenesis.

“…Evidence of effects on mixed-function oxidase and P450 enzyme systems has also been reported. In addition to effects on enzymes, it appears that garlic compounds may scavenge radicals and inhibit promotion-mechanisms considered later in this review (18).…”

“…These mechanisms include enzyme induction, mutagen scavenging, and blocking of mutagen activation. As Environmental Health Perspectives Garlic extract and many of its components exhibit activity against a wide range of chemical mutagens and radiation (18).…”

Chemopreventive Effects of Scordinin on Diethylnitrosamine and Phenobarbital‐induced Hepatocarcinogenesis in Male F344 Rats

“…[6][7][8] Garlic (Allium sativum) and related allium foods have been widely used as a popular remedy for various ailments and physiological disorders. [9][10][11] Many organosulfur compounds have been purified from garlic and they have been reported to have antioxidant, antibiotic and detoxifying properties. [9][10][11] In epidemiological studies, protective activity of garlic has been proved in some organs.…”

“…[9][10][11] Many organosulfur compounds have been purified from garlic and they have been reported to have antioxidant, antibiotic and detoxifying properties. [9][10][11] In epidemiological studies, protective activity of garlic has been proved in some organs. [12][13][14][15][16] Animal studies have also provided evidence that garlic and associated organosulfur compounds inhibit the development of neoplasms in skin, lung, stomach, esophagus, colon, mammary gland, liver and oral cavity.…”

“…[12][13][14][15][16] Animal studies have also provided evidence that garlic and associated organosulfur compounds inhibit the development of neoplasms in skin, lung, stomach, esophagus, colon, mammary gland, liver and oral cavity. 17,18) Garlic contains a complex mixture of allyl sulfur compounds that have been shown to afford protection against carcinogenesis. Diallyl sulfide (DAS) and diallyl disulfide (DADS), which are representative lipid-soluble allyl sulfur compounds present in garlic, have been extensively studied from the viewpoint of chemopreventive effects.…”