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Research sheds light on possible tumor-taming properties of vegetables and herbs

MONDAY, Oct. 31, 2005 (HealthDay News) -- Broccoli sprouts, cabbage, ginkgo biloba and garlic appear to have a role in preventing a variety of cancers, researchers report.

The research, which focuses on chemical interactions between compounds found in foods and the body's cells and DNA, suggests the addition of these foods to the diet can confer health benefits, the researchers said.

The findings were to be presented Monday at the American Association for Cancer Research's meeting, in Baltimore.

In the first study, Akinori Yanaka and colleagues from the University of Tsukuba in Japan found that in 20 people, a diet rich in broccoli sprouts significantly reduced Helicobacter pylori (H. pylori) infection. H. pylori, a bacterium, is a cause of gastritis -- inflammation of the stomach lining -- and is a major factor in peptic ulcer and stomach cancer, the researchers said.

"Even though we were unable to eradicate H. pylori, to be able suppress it and relieve the accompanying gastritis by means as simple as eating more broccoli sprouts is good news for the many people who are infected," Yanaka said in a prepared statement.

Sulforaphane, a chemical found in broccoli sprouts, appears to be the active cancer-fighting agent. Sulforaphane apparently helps cells defend against oxidants, the highly reactive and toxic molecules that damage DNA and kill cells and potentially lead to cancer, the researchers noted.

Another study with broccoli sprouts found that when an extract from the sprouts was applied to the skin of hairless mice, it counteracted carcinogenic responses to ultraviolet light exposure, a cause of skin cancer.

"Just when we stopped exposing the mice to UV light, we started applying broccoli sprout extract," said Albena T. Dinkova-Kostova, a postgraduate fellow at Johns Hopkins University. "We found that only 50 percent of mice treated with the extract developed tumors, compared with 100 percent of the mice not treated with the extract," she said.

"The topical application of this extract could be developed to be a potential agent against UV light-induced skin cancer," she added.

Dinkova-Kostova's team is studying whether ingesting broccoli sprouts for the sulforaphane might also work in protecting mice from getting skin cancer. Her hope is to see if either ingested or topical sulforaphane can protect people from skin cancer. "This strategy is probably worthwhile to be developed for protection in humans," she said.

In the third study, researchers suggest that cabbage and sauerkraut may protect women from breast cancer.

Data collected from the U.S. component of the Polish Women's Health Study showed an association between eating cabbage and sauerkraut and a lower risk of breast cancer. The effect seemed to be highest among women who eat high amounts starting in adolescence and continue to do so throughout adulthood. The most protective effect appeared to come from raw or briefly cooked cabbage, the researchers said.

"The observed pattern of risk reduction indicates that the breakdown products of glucosinolates in cabbage may affect both the initiation phase of carcinogenesis -- by decreasing the amount of DNA damage and cell mutation -- and the promotion phase -- by blocking the processes that inhibit programmed cell death and stimulate unregulated cell growth," lead researcher Dorothy Rybaczyk-Pathak, a professor of epidemiology at the University of New Mexico, said in a prepared statement.

In the fourth study, researchers from Brigham and Woman's Hospital in Boston found that ginkgo biloba appears to lower the risk of developing ovarian cancer.

"There are herbal supplements used in the treatment of cancer, although there is not much scientific evidence to support their use," said lead researcher Bin Ye. "Our study looked at ginkgo use in women with and without cancer.

"We found in a population-based study that 4.2 percent of cancer-free women reported taking ginkgo biloba regularly," Ye said. "However, only 1.6 percent of women with ovarian cancer reported taking ginkgo regularly."

In laboratory studies, the researchers found that compounds in ginkgo biloba -- ginkgolide A and B -- were the most active components contributing to this protective effect. "We found that the proliferation rates in certain types of cancer cells was inhibited by 80 percent," Ye said.

"This combination of population and laboratory studies suggests that ginkgo biloba may have value for the prevention of cancer," Ye said.

In the final study, researchers found that garlic may help ward off carcinogens produced by meat cooked at high temperatures. Cooking meats and eggs at high temperatures releases a chemical called PhIP, which may be a carcinogen.

Studies have shown that breast cancer is higher among women who eat large amounts of meat, although fat and caloric intake and hormone exposure may contribute to this increased risk, the researchers reported.

However, diallyl sulfide (DAS), a flavor component of garlic, appears to inhibit the effects of PhIP that can cause DNA damage or transform substances in the body into carcinogens.

"We treated human breast epithelial cells with equal amounts of PhIP and DAS separately, and the two together, for periods ranging from three to 24 hours," Ronald D. Thomas, associate professor of basic sciences at Florida A&M University, said in a statement. "PhIP induced expression of the cancer-causing enzyme at every stage, up to 40-fold, while DAS completely inhibited the PhIP enzyme from becoming carcinogenic," he said.

"The finding demonstrates for the first time that DAS triggers a gene alteration in PhIP that may play a significant role in preventing cancer, notably breast cancer, induced by PhIP in well-done meats," the researchers reported.

All of these findings come on the heels of a sixth study, reported in last week's issue of The Lancet, that found that people with a genetic susceptibility to lung cancer could cut their risk for the disease by eating vegetables from the cabbage family.

"We found protective effects with at least weekly consumption of cruciferous vegetables," said lead researcher Paul Brennan of the International Agency for Research on Cancer in Lyon, France.

One expert said the results of the six studies are interesting. And while it may be some time before they have any practical applications for people, that should not stop us from adding more vegetables and fruits to our diet.

"An extensive body of epidemiologic evidence suggests consistently, if not decisively, that generous consumption of fruits and vegetables is associated with reduced cancer risk," said Dr. David L. Katz, an associate professor of public health and director of the Prevention Research Center at Yale University School of Medicine.

Further study should provide "a clearer picture both of what foods reduce cancer risk, and how," Katz said. "Understanding in each of these areas will lead to new insights in the other. A refined ability to use diet in the prevention of cancer will ensue."

"That is an exciting prospect," he added. "But excitement about what may come should not distract from what is already in hand. Even with gaps in our knowledge, the case for increasing fruit and vegetable consumption to promote health and prevent disease -- cancer included -- is compelling and strong."

More information

To learn more about diet and cancer, visit the American Cancer Society.

SOURCES: Albena T. Dinkova-Kostova, Ph.D., postgraduate fellow, Johns Hopkins University, Baltimore; Bin Ye, Ph.D., researcher, Brigham and Women's Hospital, Boston; David L. Katz, M.D., M.P.H., associate professor, public health, and director, Prevention Research Center, Yale University School of Medicine, New Haven, Conn.; Oct. 31, 2005, presentations, American Association for Cancer Research meeting, Baltimore
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