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Flavonoids May Fight Ovarian, Breast Cancers

Laino, Charlene

doi: 10.1097/01.COT.0000295052.28145.65
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WASHINGTON, DC—Potent phytochemicals found in tea can help ward off ovarian and breast cancers, new research presented here at the American Association for Cancer Research suggests.

Broccoli and kale are also rich sources of cancer-fighting flavonoids, said Margaret A. Gates, a doctoral candidate at Harvard School of Public Health who has been studying their link to ovarian cancer.

Her research suggests that women who increase their consumption of kaempferol, a type of flavonoid, can lower their risk of ovarian cancer by about one third.

A second study shows that women who consume a diet rich in other types of flavonoids—specifically, flavones, flavan-3-ols, and lignans—can reduce their chance of developing breast cancer by 26% to 39%.

If patients can't keep all those scientific names straight, no worries: It basically comes down to the same foods, the researchers told OT.

For lowering ovarian cancer risk, “tea in particular may be important,” Ms. Gates said.

For breast cancer protection, “tea again is the predominant contributor,” said Brian Fink, MPH, a doctoral candidate at the University of North Carolina at Chapel Hill.

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Kaempferol Fights Ovarian Cancer

Dr. Gates analyzed data on 66,384 participants of the Nurses' Health Study, none of whom had ovarian cancer at the start of the study. Every few years, beginning in 1984, the women filled out detailed questionnaires that asked about their consumption of some 120 foods.

Using the data, the researchers calculated each participant's intake of five different flavonoids—myricetin, kaempferol, quercetin, luteolin, apigenin—and total flavonoids. Between 1984 and 2002, a total of 344 of the women were diagnosed with ovarian cancer.

Dr. Gates said there was no link between total flavonoid consumption and ovarian cancer. Nor did luteolin or apigenin significantly affect risk. There was a suggestion that myricetin and quercetin might be protective, but the association did not reach statistical significance.

But the greater the consumption of kaempferol—which the nurses got mostly from tea, broccoli, and kale—the lower the chance they developed ovarian cancer. Specifically, those in the highest quintile of kaempferol intake were 34% less likely to develop the cancer than those in the lowest quintile were.

So just how much kaempferol is enough? Dr. Gates said that 10 to 12 milligrams a day, the amount found in four cups of tea or two cups of broccoli daily, appears to be protective.

Both green tea and black tea will do the trick, she added.

Dr. Gates said she'd like to see further research in this area.

“If confirmed, flavonoid consumption would provide an important target for ovarian cancer protection,” she said.

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Flavonoid-Breast Cancer Link

To look at the flavonoid-breast cancer link, Dr. Fink studied data from a large study of breast cancer rates and risk factors conducted among women aged 20 to 98 living in Long Island, NY, in the mid-1990s.

In 1996 and 1997, nearly 3,000 participants were interviewed at home about their lifestyle habits and given questionnaires that asked what they ate and how much they ate.

Among those respondents for whom menopausal status was known, 457 premenopausal women and 977 postmenopausal women developed breast cancer. Anther 487 premenopausal women and 953 postmenopausal women did not develop cancer and served as controls.

The study showed that postmenopausal women who consumed the most flavonoids were 46% less likely to develop breast cancer, compared with those who consumed the least. But the potent chemicals had no effect on risk in premenopausal women.

When the researchers looked at specific flavonoids in the postmenopausal women, they found that flavones reduced breast-cancer risk by 39%; flavan-3-ols reduced it by 26%, and lignans, by 31%.

In addition to tea, green salad, tomatoes, and apples are all good sources of the breast cancer-fighting flavonoids, Dr. Fink said. Other flavonoids, including flavanones, isoflavones, and anthocyanidins, showed no relationship to cancer risk.

“Tiny differences in chemical structure could determine why one flavonoid is protective and another is not,” he added. “More study is needed.”

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Promising Area of Research

Cedric Garland, DrPH, Professor in Family and Preventive Medicine at the University of California, San Diego, agreed that flavonoids are a promising area of research for cancer prevention.

He noted that flavonoids are available in supplement form. The problem: “The research is only beginning to be done so we don't yet know how much to recommend,” he said.

The moderator of a news conference at which the studies were highlighted, William G. Nelson, MD, PhD, Professor of Oncology, Urology, Pharmacology, Medicine, Pathology, and Radiation Oncology at Johns Hopkins University, noted that cruciferous vegetables are potent sources of flavonoids as well as other cancer-fighting substances such as sulforaphanes.

“You can't go wrong recommending that your patients consume more of these foods,” Dr. Nelson said.

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Noninvasive Imaging Technique Developed

Researchers have devised a way to non-invasively image subjects—nuclear spin noise imaging. While this method has the advantage over MRI of not using radiofrequency radiation, it is inherently less sensitive, according to a study published in Proceedings of the National Academy of Sciences (2006;103:6790).

“At this point of course it's not a replacement for conventional MRI, but it is a very intriguing way of doing things that are minimally invasive,” study coauthor Alexej Jerschow, PhD, Assistant Professor in the Department of Chemistry at New York University, said in an interview.

While Dr. Jerschow and his coresearcher, Professor Norbert Müller of the Institute of Organic Chemistry at Johannes Kepler University in Linz, Austria, have not yet defined specific applications for this technique in the medical field, they note that it could be useful for cases in which x-ray and radiofrequency radiation are contraindicated for technical or safety reasons, such as when a very portable device is necessary or when the sample being imaged has a lengthy longitudinal relaxation time—the time it takes for the excited sample to return to equilibrium.

The technique has potential applicability in cases in which x-ray and radiofrequency radiation are contraindicated for technical or safety reasons, such as when a portable device is necessary or when the sample being imaged has a lengthy longitudinal relaxation time.

Outside the medical field, nuclear spin imaging could be valuable for analyzing explosives, since energy isn't added to the sample during imaging.

While MRI detects a signal by flipping magnetization from the equilibrium position and inducing current in the coil, nuclear spin noise imaging examines the sample at equilibrium and measures statistical fluctuations of the magnetic moments, Dr. Jerschow said.

There are also ways to refine the technique, he added. “One of the things that will make this method very powerful is to work on designing better and more sensitive detection schemes, detection apparatus—radiofrequency coils with very highly tuned circuits—that would make the signal much stronger and much more easily detectable.”

© 2006 Lippincott Williams & Wilkins, Inc.
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