Herbalists have prescribed garlic to treat infections, heart ailments, and other maladies since at least the Middle Ages. In the past few decades, scores of scientific studies have begun identifying solid mechanistic underpinnings for many such age-old claims -- and a few newer ones, such as the pungent bulb's potential for fighting cancer.
"Raw garlic is good as an antimicrobial substance, where it can save people from infections," notes Barbara Levine, director of the Garlic Information Center in New York. She says garlic has also been shown to enhance immunity, protect the nervous system, and foster a whole host of heart-healthy effects -- from thinning the blood and reducing blood pressure to lowering cholesterol concentrations (Fish oil gets a garlic chaser for the heart).
Donning her second hat, director of nutrition research at the Strang-Cornell Cancer Research Laboratory, she points out that this food also appears quite promising as a source of chemical ammunition against many cancers. For instance, she notes, "garlic consumption in humans has been significantly correlated with a decreased risk of stomach cancer."
Consumers today have access to many different types of garlic -- raw cloves for salads, bottled juice and dried powders for cooking, and capsules or pills made from garlic extracts for supplementing the diet.
The important thing to realize, Levine points out, is that different forms of garlic may be enriched in -- or depleted of -- any or many of the biologically active ingredients responsible for garlic's reputed health benefits.
A new study by Mazhar N. Malik at the New York State Institute for Basic Research on Staten Island found that garlic contains a significant amount of vitamin E. Indeed, his team's analyses in last month's Journal of Agricultural and Food Science indicated that there was about 0.015 International Unit (IU) of the vitamin per gram of garlic -- or roughly 100 times more than had been reported previously.
However, the type of vitamin E differed, depending on whether the garlic they studied was fresh, had been safely aged in their refrigerator for about 2 years, or was extracted from commercial garlic supplements. While the fresh, raw garlic's vitamin E consisted almost exclusively of alpha-tocopherol -- the form also found in most vitamin supplements -- there was almost no alpha form in the garlic pills they analyzed and absolutely no detectable alpha in the aged garlic. Instead, the latter two types of garlic contained mostly delta- or gamma-tocopherol, types that the body appears to use differently from the alpha form (SN: 4/5/97, p. 207).
Such data illustrate, Levine says, that there's no reason to expect all forms of garlic to be equally effective at fostering a particular biological benefit. Indeed, she notes, one recent British study showed that cholesterol concentrations in the blood fell when people supplemented their diet with garlic pills but not when they consumed the garlic powder used in cooking.
As they mature, wines undergo a complex series of chemical changes that may not only improve their flavor and aroma but cut some of the acidic bite that can mar the appeal of younger vintages.
Similarly, garlic undergoes a suite of chemical alterations as it ages, notes nutritionist Brenda L. Petesch of Wakunaga of America Co., a maker of garlic supplements. She says that her company ages sliced, organically grown garlic in tanks for up to 20 months to remove some of the objectionable odors associated with the raw bulb and to give it a milder flavor.
Research on these over-the-counter aged-garlic products -- or pure compounds extracted from garlic -- is probing how they may affect the development of cancer. Data from several such studies emerged last week at the Experimental Biology '97 meeting in New Orleans.
John T. Pinto and his colleagues at the Memorial Sloan-Kettering Cancer Center reported on the unusual ability of SAMC (S-allyl mercaptocysteine) to inhibit the development -- and perhaps the spread -- of prostate cancer. While SAMC occurs in fresh garlic, it is concentrated by aging.
In test-tube studies, the compound proved especially effective at retarding the proliferation of prostate cancer cells (Aged garlic could slow prostate cancer). Moreover, these and related anticancer effects that the group described occurred even at relatively low doses -- and at concentrations comparable to those that could be found in the blood of people taking aged-garlic pills. It is unlikely that one could eat enough fresh garlic to attain these concentrations, the researchers note.
Fresh garlic also has its benefits
Scientists from Pennsylvania State University in State College reported a trio of promising cancer studies using garlic constituents, many derived from fresh garlic, at the New Orleans meeting.
Working with colon cancer cells grown in the lab, Lynn M. Knowles and John A. Milner compared DADS (diallyl disulfide), a constituent of garlic oil capsules, against two water-soluble compounds in aged garlic: SAMC and SAC (S-allyl cysteine).
While no amount of SAC cut the cells' proliferation, SAMC was effective. However, it took 12 times as much SAMC to achieve the same effect on tumor cell proliferation as they got with DADS.
"We knew that DADS at almost any concentration would slow cancer cell growth, but we didn't know how," explains Knowles.
What her study demonstrated was that during the 24-hour period after exposure, the treated cancer cells initiated a process that readies them to divide. First, the cells evaluated whether to synthesize new genetic material. Then, they copied the new DNA, making a duplicate of the original. During the next stage, the cells determined whether they had made that copy accurately. Normally, the next step would be for the cell to divide in two. It was at this point, Knowles says, "that garlic halted them."
However, this inhibition of the cell cycle proved "transitory," she notes, in that "the cells do recover" -- unless exposure to garlic continues.
Last year, Milner and Mark E. Dion presented data at the Experimental Biology meeting on garlic's role in a different area: the body's ability to produce nitrosamines, a type of potent carcinogen. They showed that fresh garlic (Allium sativum), fresh elephant garlic (A. ampeloprasum), and Kyolic (a Wakunaga aged-garlic product) "were all very effective in suppressing the spontaneous formation of nitrosamines," Milner recalls.
Onions (A. cepa), which belong to the same family as garlic, also suppressed nitrosamine formation, but, Milner observes, "onions didn't do it nearly as well as garlic. And leeks [A. tricoccum] didn't do anything -- so you can't assume that all allium foods are the same [in this respect]."
This year, Dion and Milner decided to investigate one of the enzyme systems in the body responsible for activating certain nitrosamines into compounds capable of damaging DNA.
They fed either Kyolic garlic extracts or DADS to young rats for a period of 2 weeks. Each animal was then given a muscle relaxant that the body processes via the same enzyme system believed to be responsible for transforming most dietary nitrosamines into carcinogens. In this sense, the drug they used served as a nontoxic surrogate to study one of the mechanisms by which cancers may form.
Both types of garlic compounds reduced the amount of the activated compound present in urine -- a gauge of what the body had produced. However, DADS was almost twice as potent as the aged-garlic extract in limiting activation of this carcinogen model.
A garlicky link between heart and cancer protection
Finally, Milner and Eric M. Schaffer showed that DADS can depress the activity of cyclooxygenase, an enzyme. Because this enzyme plays a role in elevating blood pressure, raising concentrations of cholesterol in the blood, and fostering a number of cancer processes, "this finding could have profound implications," Milner told Science News Online. Indeed, he said, DADS seems to work through this enzyme in modifying heart risks, "just like ibuprofen and aspirin do."
Cyclooxygenase can also transform some chemicals into carcinogensand that's what the researchers probed in mice eating a high-fat diet.
Eating lots of fat is one way to turn on the enzyme, Milner notes, and in so doing risk damaging DNA in a way that could foster cancer. In their rats, however, DADS suppressed the activity of the enzyme. When the animals were exposed to a precarcinogen, they proved less able to fashion a carcinogen out of it.
Can people get enough DADS from garlic in the diet or in aged-garlic supplements to ratchet down cyclooxygenase's carcinogen production? "I don't know," Milner says, "but we hope so." In any case, he adds, "It's really kind of a fun story."
While the details of how garlic functions are only now coming to light, Levine says they have "enough evidence from human studies showing that it lowers blood pressure, lowers cholesterol, and enhances the immune system to warrant the use of garlic." Clearly, she says, "we really should eat more of it."
As a nutraceutical -- that is, a food with health benefits -- it represents a good adjunct to medicine, she says. "What we're saying is that if it works, it may possibly enhance one's degree of protection [from disease]." However, she emphasizes, "it's not an alternative to medicine." So if you're taking medicine now, "don't go off it. We're not touting any of this as a cure."
Interestingly, she points out, about 75 percent or more of prescription medications have been derived from plants. "Now we're finally coming back to it" -- those natural sources, often in their natural form.
Toward that end, she shares three low-fat recipes that the Garlic Information Center has developed to help incorporate more garlic into the diet.
4 heads of garlic
10 oz. can white beans
Preheat oven to 350°F. Remove outer, papery skin from garlic, leaving the whole head intact. Arrange garlic heads in a small baking dish. Pour chicken stock over the garlic, cover tightly with foil, and bake -- basting frequently -- for 1 hour (add more stock or water, if needed).
Uncover and bake 15 minutes more. Remove from oven and cool.
While garlic is baking, place beans, oil, rosemary, thyme, and water into a food processor and puree into a smooth, thick consistency.
Squeeze cooled garlic from the individual cloves into the bean mix. Puree again until smooth. Season with salt and serve instead of butter with crusty bread or crostini.
NUTRIENTS (per serving):
Protein: 4 grams
Carbohydrates: 11 grams
3 large stalks of broccoli, ends trimmed
1/2 cup red wine
Sauté garlic in olive oil until lightly browned. Add chopped pepper and sauté for another minute. Pour wine into sauté pan (can substitute 1 Tbs. balsamic vinegar and 1/2 cup water) and boil for 1 to 2 minutes to reduce liquid. Add broccoli, cover, and simmer until the broccoli is tender. If the liquid evaporates before broccoli is cooked, add a small amount more.
NUTRIENTS (per serving):
Protein: 3 grams
Carbohydrates: 7 grams
3 heads roasted garlic
1 tsp. pepper
Puree mustard, salt, anchovies, lemon juice, water, vinegar, and roasted garlic heads (see roasting instructions under recipe for bean spread) in food processor. Slowly drizzle olive oil in until the mix is well emulsified. Season with salt and add parmesan cheese.
NUTRIENTS (per serving):
Protein: 1 gram
Carbohydrates: 4 grams
Dion, M.E., M. Agler, and J.A. Milner. In press. S-allyl-cysteine inhibits nitrosomorpholine formation and bioactivation. Nutrition and Cancer 28:1.
Dion, M.E., and J.A. Milner. 1997. Garlic inhibits cytochrome P450 2E1 -mediated chlorzoxazone metabolism (Abstract #2144). FASEB Journal 11(Feb. 28):A370.
Knowles, L.M., and J.A. Milner. 1997. Garlic constituents alter cell cycle progression and proliferation (Abstract #2445). FASEB Journal 11(Feb. 28):A422.
Malik, M.N., et al. 1997. Isolation of alpha-tocopherol (vitamin E) from garlic. Journal of Agricultural and Food Chemistry 45(March):817
Pinto, J., et al. 1997. Garlic constituents modify expression of biomarkers for human prostatic carcinoma cells (Abstract #2541). FASEB Journal 11(Feb. 28):A439.
Schaffer, E.M., and J.A. Milner. 1997. Cyclooxygenase-mediated formation of 7,12-dimethylbenz(a)anthracene (DMBA)-induced mammary DNA adducts (Abstract #2548). FASEB Journal 11(Feb. 28):A440.
Pinto, J.T., and R.S. Rivlin. In press. Garlic and prevention of prostate cancer. In Designer Foods III, P. Lachance and H. Pierson, ed. Westport, Conn.: Food and Nutrition Press.
Raloff, J. 1997. Aged garlic may slow prostate cancer. Science News 151(Apr. 19): 239.
Raloff, J. 1997. Health benefits of another vitamin E. Science News 151(April 5):207/.
Raloff, J. 1997. The rise of nutraceuticals. Science News Online(Feb. 15).
Garlic Information Center
New York Hospital-Cornell University Medical Center
515 E. 71st St., S 904
New York, NY 10021
Toll-free Phone: 800-330-5922
Kyolic Aged Garlic Extract
Wakunaga of America Co., Ltd.
Mission Viejo, CA 92691
Mazhar N. Malik
Departments of Pharmacology and Pathological Neurobiology
New York State Institute for Basic Research
1050 Forest Hill Rd.
Staten Island, NY 10314
John A. Milner
Department of Nutrition
126 Henderson Bldg. South
Pennsylvania State University
University Park, PA 16802
Memorial Sloan-Kettering Cancer Center
1275 York Ave., Box 140
New York, NY 10021
This week's Food for Thought is prepared by Janet Raloff, senior editor of Science News.