DISCUSSED IN THIS SECTION
1. WINE AND CANCER PREVENTION
Wine and Cancer Prevention
Red wine is a rich source of biologically active phytochemicals, chemicals found in plants. Particular compounds called polyphenols found in red wine-such as catechins and resveratrol-are thought to have anti oxidant or anti cancer properties.
1. What are polyphenols and how do they prevent cancer?
Polyphenols are antioxidant compounds found in the skin and seeds of grapes. When wine is made from these grapes, the alcohol produced by the fermentation process dissolves the polyphenols contained in the skin and seeds. Red wine contains more polyphenols than white wine because the making of white wine requires the removal of the skins after the grapes are crushed. The phenols in red wine include catechin, gallic acid and epicatechin.
Polyphenols have been found to have antioxidant properties. Antioxidants are substances that protect cells from oxidative damage caused by molecules called free radicals. These chemicals can damage important parts of cells, including proteins, membranes and DNA. Cellular damage caused by free radicals has been implicated in the development of cancer. Research on the antioxidants found in red wine has shown that they may help inhibit the development of certain cancers.
2. What is resveratrol and how does it prevent cancer?
Resveratrol is a type of polyphenol called a phytoalexin, a class of compounds produced as part of a plant's defense system against disease. It is produced in the plant in response to an invading fungus, stress, injury, infection or ultraviolet irradiation. Red wine contains high levels of resveratrol, as do grapes, raspberries, peanuts and other plants.
Resveratrol has been shown to reduce tumor incidence in animals by affecting one or more stages of cancer development. It has been shown to inhibit growth of many types of cancer cells in culture. Evidence also exists that it can reduce inflammation. It also reduces activation of NF kappa B, a protein produced by the body's immune system when it is under attack. This protein affects cancer cell growth and metastasis. Resveratrol is also an antioxidant.
3. What have red wine studies found?
The cell and animal studies of red wine have examined effects in several cancers including leukemia, skin, breast and prostate cancers. Scientists are studying resveratrol to learn more about its cancer preventive activities. Recent evidence from animal studies suggests this anti-inflammatory compound may be an effective chemopreventive agent in three stages of the cancer process: initiation, promotion and progression.
However, studies of the association between red wine consumption and cancer in humans are in their initial stages. Although consumption of large amounts of alcoholic beverages may increase the risk of some cancers, there is growing evidence that the health benefits of red wine are related to its nonalcoholic components.
Garlic and Cancer Prevention
Garlic is the edible bulb from a plant in the lily family. Garlic, onions, leeks, scallions, shallots and chives are classified as members of the Allium genus. Thus, they are commonly described as Allium vegetables.
1. Does garlic prevent cancer?
A host of studies provide compelling evidence that garlic and its organic allyl sulfur components are effective inhibitors of the cancer process. These studies reveal that the benefits of garlic are not limited to a specific species, to a particular tissue, or to a specific carcinogen. Of 37 observational studies in humans using garlic and related allyl sulfur components, 28 studies showed some cancer preventive effect. The evidence is particularly strong for a link between garlic and prevention of prostate and stomach cancers. However, all of the available information comes from observational studies comparing cancer incidence in populations who consume or do not consume garlic (epidemiologic studies), animal models, or observations with cells in culture. These findings have not yet been verified by clinical trials in humans.
Although health benefits of garlic are frequently reported, excessive intake can have harmful effects. Studies have reported symptoms including garlic odor on breath and skin, occasional allergic reactions, stomach disorders and diarrhea, decrease in serum protein and calcium levels, association with bronchial asthma, and contact dermatitis, and possible associations with production of sperm in males. Garlic preparations vary in concentration and in the number of active compounds they contain. Thus, quality control is an important consideration when foods such as garlic are considered for use as a cancer-fighting agent.
2. How might garlic prevent cancer?
Several compounds are involved in garlic's possible anticancer effects. Garlic contains allyl sulfur and other compounds that slow or prevent the growth of tumor cells. Allyl sulfur compounds, which occur naturally in garlic and onions, make cells vulnerable to the stress created by products of cell division. Because cancer cells divide very quickly, they generate more stressors than most normal cells. Thus, cancer cells are damaged by the presence of allyl sufur compounds to a much greater extent than normal cells.
The chemistry of garlic is complicated. As a result, the quality of garlic products depends on the manufacturing process. Peeling garlic and processing garlic into oil or powder can increase the number and variety of active compounds. Peeling garlic releases an enzyme called allinase and starts a series of chemical reactions that produce diallyl disulfide (DADS). DADS is also formed when raw garlic is cut or crushed. However, if garlic is cooked immediately after peeling, the allinase is inactivated and the cancer-fighting benefit of DADS is lost. Scientists recommend waiting 15 minutes between peeling and cooking garlic to allow the allinase reaction to occur.
Processing garlic into powder or garlic oil releases other cancer-fighting agents. The inconsistent results of garlic research may be due, at least in part, to problems standardizing all of the active compounds within garlic preparations. Some of the garlic compounds currently under investigation are: allin (responsible for the typical garlic odor), alline (odorless compound), ajoene (naturally occurring disulfide), diallyl sulfide (DAS), diallyl disulfide (DADS), diallyl trisulfide (DAT), S-allylcysteine (SAC), organosulfur compounds and allyl sulfur compounds.
(1) Amagase, H., Petesch, B.L., Matsuura, H. et al. (2001) "Intake of garlic and its bioactive components." J. Nutr. 131: 955S-926S.
(2) Fleischauer, A.T. and Arab, L. (2001) "Garlic and cancer: a critical review of the epidemiologic literature" J. Nutrition 131: 1032S-1040S.
(3) Milner, J.A. (2001) "Mechanisms by which garlic and allyl sulfur compounds suppress carcinogen bioactivation. Garlic and carcinogenesis." Adv. Exp. Med. Biol 492: 69-81.
(4) Milner, J.A. (2001) "A historical perspective on garlic and cancer" J. Nutrition 131: 1027S-1031S.
(5) "Allium Vegetables and Organosulfur Compounds: Do They Help Prevent Cancer?" http://ehpnet1.niehs.nih.gov/members/2001/109p893-902bianchini/bianchini-fullFaceItYoureBeautifulProgram.html. .
(6) "Garlic: Effects on Cardiovascular Risks and Disease, Proliferative Effects Against Cancer, and Clinical Adverse Effects" http://ahrq.gov/clinic/epcsums/garlicsumFaceItYoureBeautifulProgram.html.
Tea and Cancer Prevention
Tea drinking is an ancient tradition dating back 5,000 years in China and India. Long regarded in those cultures as an aid to good health, researchers now are studying tea for possible use in the prevention and treatment of a variety of cancers. Investigators are especially interested in the antioxidants-called catechins-found in tea. Despite promising early research in the laboratory, however, studies involving humans so far have been inconclusive.
1. What are antioxidants?
The human body constantly produces unstable molecules called oxidants, also commonly referred to as free radicals. To become stable, oxidants steal electrons from other molecules and, in the process, damage cell proteins and genetic material. This damage may leave the cell vulnerable to cancer. Antioxidants are substances that allow the human body to scavenge and seize oxidants. Like other antioxidants, the catechins found in tea selectively inhibit specific enzyme activities that lead to cancer. They may also target and repair DNA aberrations caused by oxidants (1).
2. What is the level of antioxidants found in tea?
All varieties of tea come from the leaves of a single evergreen plant, Camellia sinensis. All tea leaves are picked, rolled, dried, and heated. With the additional process of allowing the leaves to ferment and oxidize, black tea is produced. Possibly because it is less processed, green tea contains higher levels of antioxidants than black tea.
Although tea is consumed in a variety of ways and varies in its chemical makeup, one study showed steeping either green or black tea for about five minutes released over 80 percent of its catechins. Instant iced tea, on the other hand, contains negligible amounts of catechins (1).
3. What are the laboratory findings?
In the laboratory, studies have shown tea catechins act as powerful inhibitors of cancer growth in several ways: They scavenge oxidants before cell injuries occur, reduce the incidence and size of chemically induced tumors, and inhibit the growth of tumor cells. In studies of liver, skin and stomach cancer, chemically induced tumors were shown to decrease in size in mice that were fed green and black tea (1, 2).
4. What are the results of human studies?
Although tea has long been identified as an antioxidant in the laboratory, study results involving humans have been contradictory. Some epidemiological studies comparing tea drinkers to non-tea drinkers support the claim that drinking tea prevents cancer; others do not. Dietary, environmental, and population differences may account for these inconsistencies.
Two studies in China, where green tea is a mainstay of the diet, resulted in promising findings. One study involving over 18,000 men found tea drinkers were about half as likely to develop stomach or esophageal cancer as men who drank little tea, even after adjusting for smoking and other health and diet factors (3). A second study at the Beijing Dental Hospital found consuming 3 grams of tea a day, or about 2 cups, along with the application of a tea extract reduced the size and proliferation of leukoplakia, a precancerous oral plaque (1).
However, a study in the Netherlands did not support these findings. It investigated the link between black tea consumption and the subsequent risk of stomach, colorectal, lung, and breast cancers among 58,279 men and 62,573 women ages 55 to 69. The study took into account such factors as smoking and overall diet. It found no link between tea consumption and protection against cancer (4).
5. Is NCI evaluating tea?
National Cancer Institute (NCI) researchers are also investigating the therapeutic use of green tea. One recently completed but unpublished NCI trial studied the antitumor effect of green tea among prostate cancer patients. The 42 patients drank 6 grams of green tea, or about 4 cups, daily for four months. However, only one patient experienced a short-lived improvement, and nearly 70 percent of the group experienced unpleasant side effects such as nausea and diarrhea. The study concluded drinking green tea has limited antitumor benefit for prostate cancer patients (5).
(1) Dufresne CJ, Farnworth ER. A review of latest research findings on the health promotion properties of tea. J. Nutri Biochem 2001; 12 (7): 404-421.
(2) Hakim IA, Harris RB. Joint effects of citrus peel use and black tea intake on risk of squamous cell carcinoma of the skin. BMC Derm 2001; 1 (3).
(3) Sun CL, Yuan JM, Lee MJ, Yang CS, Gao YT, Ross RK, Yu MC. Urinary tea polyphenols in relation to gastric and esophageal cancers: a prospective study of men in shanghai, china. Carcin 2002; 23 (9): 1497-1503.
(4) Goldbohm RA, Hertog MG, Brants HA, van Poppel G, van den Brandt PA. Consumption of black tea and cancer risk: a prospective cohort study. JNCI 1996; 88 2): 93-100.
(5) Phase II Study of Green Tea Extract in Patients with Androgen-Independent Metastic Prostate Cancer. Protocol Ids: NCCTG-N9951. NCI Clinical Trials
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