The meta-analysis conducted by Fleischauer, Poole, and Arab supported the inverse correlation between raw and cooked garlic consumption and colorectal and stomach cancer. On the contrary, the study conducted in the Netherlands suggested no risk of cancer due to garlic supplement consumption in a cohort that included breast cancer patients, colorectal, stomach, and lung cancer patients.1 Thus, further research is needed in order to draw a concise conclusion on the topic of correlation between raw and cooked garlic and garlic supplement consumption and causes of cancer. The study conducted by Turati et al. came to a conclusion that frequent garlic consumption reduces the possibility of colorectal cancer. It is important to note that the evidence of garlic being beneficial for reducing risks of colorectal cancer was predominantly drawn from the case-control studies due to the fact that studies that involved cohort gave no sufficient results.2 Furthermore, the study detected a correlation between increased intake of allium vegetables (onion, garlic, leek, shallot, chives) and the possibility to reduce the instances of colorectal adenomatous polyps emergence.
Epidemiologic studies presented in Nicastro, Ross, and Milner’s article also indicated beneficial properties inherent to allium vegetables when it comes to protection against different types of cancer, especially cancer that affects the gastrointestinal tract. On the other hand, there is a difficulty in assessing the precise amount of allium vegetables required to lower the risk of cancer. Mechanistic studies included in the article suggested an anticancer activity of different allium vegetable extracts that contained compounds of sulfur.3 Such compounds have a potential to provide beneficial effects in order to modify the risk of cancer on various stages of its development.
Antimicrobial properties of garlic were also evidenced by Nicastro, Ross, and Milner. The sulfur compounds like allicin and derivatives of ajoene present in garlic are the main contributors of garlic’s antimicrobial properties. In addition, garlic’s antibacterial properties eliminate the bacteria H. pylori, which causes gastritis and then consequently gastric cancer.3 Since garlic belongs to allicin vegetables, its properties are able to inhibit the movement of neutrophic granulocytes in the epithelia, a process which occurs during the inflammation. Thus, there is evidence of the anti-inflammatory properties of garlic, like, for instance, in the mouse-model of the Morbus Bechterew’s disease which affects the vertebral body.4
Kodali and Eslick also reported positive properties of garlic in its ability to inhibit the mechanisms of cancer initiation. Garlic was evidenced to contain compounds of organosulfur, namely, diallyl trisulfide, which had a positive effect on reducing the possibility of cancer in animals selected for an experiment. The precise mechanism of inhibiting cancer emergence is still not clear; however, a hypothesis has been put forward that the compounds of sulfur are beneficial for encouraging the repair of DNA thus reducing cancer risks through detoxifying the carcinogens and inducing the production of apoptosis. Furthermore, in the process of DNA repair, the anti-bacterial properties of garlic play a crucial role.5
To conclude, the anti-inflammatory and anti-bacterial properties of garlic and other allium vegetables are able to reduce the instances of colorectal and stomach cancer. Despite the fact that the optimal consumption amount for inhibiting the cancerogenesis is unknown, the above-mentioned research did provide evidence that increased consumption of raw and cooked garlic does have an effect on cancer development. However, further research is needed to find out the optimum amount of garlic consumption in order to inhibit the production of cancerous agents.
Fleishauer AT, Poole C, Arab, L. Garlic consumption and cancer prevention: meta-analyses of colorectal and stomach cancers. Am J Clin Nutr. 2000, 72: 1047-1052.
Turati F, Guerico V, Pellucchi, C, Vecchia, C, Galeone, C. Colorectal cancer and adenomatous polyps in relation to allium vegetable intake: A meta-analysis of observational studies. Mol Nutr Food Res. 2014, 58: 1907-1914. Web.
Nicastro HL, Ross, SA, Milner. Garlic and onions: Their cancer prevention properties. Cancer Prev Res 2015; 8: 181-189. Web.
Borlinghaus J, Albrecht F, Gruhlke MCH, Nwachuckwu ID, Slusarenko AJ. Allicin: chemistry and biological properties. Molecules 2014, 19: 12591-12618. Web.
Kodali RT, Eslick GD. Meta-analysis: Does garlick intake reduce the risk of gastric cancer? Nutrition and Cancer. 2015; 67(1): 1-11. Web.