The anti-cancer properties of garlic were first recognized in the 1950's when scientists linked allicin, a principal component of garlic, to tumor inhibition. Since then scientific investigation has consistently demonstrated that regular garlic consumption can slow or prevent certain types of cancer, particularly prostate and stomach cancer. Additional studies show an association between increased intake of garlic and reduced risk of stomach, colon, esophageal, pancreatic, and breast cancer. Though some studies have found otherwise, the inconsistency is thought to be due in part to problems standardizing all of the active compounds within garlic preparations. Why is garlic so good for us and how can we benefit from this knowledge?
Garlic, the vegetable otherwise known as Allium sativum, is the edible bulb produced by a plant in the lily family. Onions, chives, leeks, shallots, and scallions are also in the allium class of bulb-shaped plants, but garlic is unique in this group because of its high sulfur content. Garlic contains health-promoting antioxidants and selenium, but its anti-cancer effects, along with its breath-flavoring properties, come from the bioactive sulfur compounds formed from allicin when garlic is chopped or crushed. Components of garlic being studied for anti-cancer activity include allin (responsible for the typical garlic odor), alline (an odorless compound), ajoene (a naturally occurring disulfide), diallyl sulfide (DAS), diallyl disulfide (DADS), diallyl trisulfide (DAT), S-allylcysteine (SAC), organosulfur compounds, and allyl sulfur compounds.
These sulfur compounds can inhibit the production of cancer-causing agents, halt rapidly dividing cancer cells, and even trigger the death of cancer cells. Both allicin and allyl sulfur have been found to inhibit or slow cancer growth in animals, and populations studies show that cultures consuming an above average amount of garlic have lower incidences of certain types of cancers. But to get these benefits from garlic the vegetable has to be prepared just right.
To benefit from garlic's anticancer properties, the vegetable preparation must allow time for the chemical reactions producing sulfur compounds to occur. Pressing garlic into powder or oil and peeling garlic will release active anti-cancer compounds, though you should wait at least 15 minutes after peeling to cook the garlic to allow adequate time for the necessary chemical reactions to take place. Using these simple techniques to flavor your food is a reasonable way to take advantage of the health properties of garlic. But consuming excessive amounts of garlic can have a negative impact on health, so don't overdo it.
Excessive garlic intake can irritate the stomach, leading to heartburn, nausea, and vomiting, and stimulation of the bowel can cause severe diarrhea. Large amounts of garlic can also lead to bad breath, skin reactions, and worsening of asthma. Garlic may interfere with several medications, including the anti-HIV agent saquinavir (Invirase and Fortovase), and it may raise insulin levels and lower blood sugar, which could be dangerous for a diabetic. Finally, the blood-thinning properties of garlic make excess consumption dangerous for people taking prescription blood-thinners like warfarin (Coumadin) or heparin (Lovenox), as well as pregnant women and people with bleeding disorders.
So while it's reasonable and may be beneficial to add extra garlic seasoning to your meals, be careful not to overdo it and be sure to let your doctor know if you are taking garlic supplements for other health reasons.. Enjoy the extra flavor of garlic in your food, and brush your tongue and gargle for one minute daily with hydrogen peroxide-containing mouthwash to remove sulfur compounds and mitigate the effects of garlic on your breath.