VEGETABLES PREVENT CANCER

VEGETABLES PREVENT CANCER

Vegetables may be one of the single most important weapons in your fight against cancer. Vegetables prevent cancer.
Most people react to such a statement by saying "Sure, we all know vegetables are good for you." But do you know how good, or why? It may seem incredible to you that simple, everyday items, like cabbage, broccoli, and carrots are more powerful weapons against cancer than all the high-tech drugs and chemotherapy.

Flavonoids

Recent studies have identified many new phytochemicals that occur in fruits and vegetables that can inhibit cell proliferation. These are the flavonoids. The classification of these flavonoids is daily becoming more complicated. We are going to look at a few of the hundreds studied to demonstrate how important it is to eat your fruits and vegetables each day. In this issue we look at two of the major classes of flavonoids -- phenols and indoles. Next issue we will look at other major flavonoids including isoflavones, coumarins and aromatic isothiocyantes.( 1)

Phenols

Various kinds of phenols occur in edible plants including one that is often sold as a sports supplement. It is 4-hydroxy-3-methoxy cinnamic acid. The popular name is ferulic acid, and it is the major active substance in gamma oryzanol, a compound extracted from rice bran oil.

Ferulic acid and at least two other plant phenols have been shown to inhibit stomach cancer deliberately induced in mice.( 2) In in-vivo and in-vitro experiments, the polyphenols ellagic acid, tannic acid, caffeic acid and ferulic acid were investigated to see if they would inhibit the growth of tumors in their initial phase of growth.( 3) Tannic acid, caffeic acid and ferulic acid were found to be the strongest tumor growth inhibitors.

Another class of phenols are those found in green and black tea. Tea is the most popular beverage, consumed by over two-thirds of the world's population. Tea is processed differently in different parts of the world to give green (20%), black (78%) or oolong tea (2%). The anti-mutagenic and anti-carcinogenic activities of green tea have been extensively examined.( 4)

The activity of tea against various mutagens has been demonstrated in microbial systems (salmonella and E. coli), in mammalian cell systems and in-vivo animal tests. The anti-carcinogenic activity of tea phenols has been shown in experimental animals such as rats and mice, in transplantable tumors, carcinogen-induced tumors in digestive organs, mammary glands, hepatocarcinomas, lung cancers, skin tumors, leukemia, tumor promotion and metastasis. Tea phenols work both inside and outside the cell environment. Let's look at some specific study examples.
The inhibitory effects of green tea on carcinogenesis have been investigated in numerous laboratory studies. One of the active ingredients, epigallocatechin gallate (EGCG) has been reported to inhibit the growth of cancer cells in animals. One recent study with 472 patients found that consumption of green tea was closely associated with decreased numbers of lymph node metastases among pre-menopausal women with stage I and II breast cancer.( 5)
They also found that increased consumption of green tea was correlated with decreased recurrence of stage I and II breast cancer.

Tea consumption also helps inhibit tumors of the digestive tract. In a study using rats with artificially induced esophagus tumors, both the incidence and the multiplicity of the tumors were decreased by green or black tea.( 6)
The group that was given green and black tea during the initial treatment with the carcinogen, had a 70% reduction in tumor growth over controls. The group given the tea after tumor growth had occurred had a tumor reduction of 55% over controls.

Green tea is good news for men also. The enzyme ornithine decarboxylase, is high in men with prostate cancer and in prostatic fluid.( 7) This enzyme is an androgen-responsive gene and the androgenic stimulation regulates the development and growth of both normal and tumorigenic prostate cells. Research using both in-vitro (test-tube) and in-vivo models (mice) has shown that green tea inhibits tumor formation by controlling the amount of ornithine decarboxylase uptake.( 8)

It may also help with inhibition of skin cancer. An in-vivo study using mice evaluated the protective effect of green tea against the change of normal cells to papillomas and consequently to squamous cell carcinomas.( 9) The researchers concluded that green tea phenols are highly useful in protecting against skin cancer risk.

Another major class of phenols is the proanthocyanidins found in pine bark, grape seeds and bilberry leaves. These have received a lot of press and are important antioxidants and anti-inflammatories. Recent research has shown them to be promising anti-tumor substances also.( 10) Other promising polyphenols are resveratrol and quercetin found in vegetables, citrus fruits and red grapes.( 11)

Indoles

Indoles occur naturally in cruciferous vegetables such as cabbage, cauliflower, broccoli and brussel sprouts. The most well known of the indoles is indole-3-carbinol. Let's look at some recent studies.

In one study, sixty women at increased risk for breast cancer were enrolled in a placebo-controlled, double-blind dose-ranging chemoprevention study of indole-3-carbinol. The results suggested that indole-3-carbinol at a minimum effective dose schedule of 300 mg per day is promising as a preventive agent for breast cancer.( 12)

A more recent study found that a combination of indole-3-carbinol and the anti-estrogen drug tamoxifen, cooperate to inhibit the growth of estrogen-dependent breast cancer more effectively than either substance alone.( 13)

Another study on rats examined indole-3-carbinol's ability to inhibit development of liver cancer when given either before or after exposure to a carcinogen.( 14) Animals that were pretreated with indole-3-carbinol for two weeks prior to administration of the carcinogen and continued to receive it during exposure to the carcinogen, were protected from development of neoplastic lesions. The animals who did not receive it prior to exposure to the carcinogen did not experience any protective effect. This study shows it is important to maintain these substances in your body all the time for them to have a protective effect.

In another issue we will look at other major classes of flavonoids -- more weapons in the war against cancer. And remember, eat your vegetables!

REFERENCES

(1.) Wattenberg LW. In Arnott MS, et al (eds). Molecular Interactions of Nutrition and Cancer. New York: Raven Press, 1982:43.

(2.) National Academy of Sciences. Diet, Nutrition and Cancer. Washington DC: National Academy Press, 1982:5-20.
(3.) Kaul A, Khanduja KL. Polyphenols inhibit promotional phase of tumorigenesis: relevance of superoxide radicals. Nutr Cancer, 1998;32: 81-5.

(4.) Kuroda Y, Hara Y. Anti-mutagenic and anti-carcinogenic activity of tea polyphenols. Mutat Res, 1999;436: 69-97.
(5.) Nakachi K, et al. Influence of drinking green tea on breast cancer malignancy among Japanese patients. Jpn J Cancer Res, 1998, 89:254-261.

(6.) Wang ZY, et al. Inhibition of N-nitrosomethylbenzylamine-induced esophageal turmoigenesis in rats by green and black tea. Carcinogenesis, 1995;16:2143-2148.

(7.) Mohan RR, et al. Over expression of ornithine decarboxylase in prostate cancer and prostatic fluid in humans. Clin Cancer Res, 1999;5:143-147.

(8.) Gupta S, et al. Prostate cancer chemoprevention by green tea: in vitro and in viva inhibition of testosterone-mediated induction of ornithine decarboxylase. Cancer Res, 1999;59:2115-2120.

(9.) Katiyar SK, et al. Protection against induction of mouse skin papillomas with low and high risk of conversion to malignancy by green tea polyphenols. Carcinogenesis, 1997;18:497-502.

(10.) Bomser JA, et al. Inhibition of induced tumor promotion in CD-1 mouse epidermis by a polyphenolic fraction from grape seeds. Cancer Lett, 1999;135:151-157.

(11.) Elattar TM, Virji AS. Modulating effect of resveratrol and quercetin on oral cancer cell growth and proliferation. Anticancer Drugs, 1999;10: 187-193.

(12.) Wang GY, et al. Dose-ranging study of indole-3-carbinol for breast cancer prevention. J Cell Biochem Suppl, 1997;28-29:111-116.

(13.) Cover CM, et al. Indole-3-carbinol and tamoxifen cooperate to arrest the cell cycle of MCF-7 human breast cancer cells. Cancer Res, 1999, 59:1244-1251.
(14.) Manson MM, et al. Chemoprevention of aflatoxin B1-induced carcinogenesis by indole-3-carbinol in rat liver - predicting the outcome using early biomarkers. Carcinogenesis, 1998;19:1829-1836.

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