The large study reviewed here found that higher blood levels of the compound genistein (pronounced jenn-is-stine) seems to be linked to a lower risk of breast cancer. Genistein is a plant isoflavone. Isoflavones are found in soybeans and chick peas.
More than 24,000 Japanese women were followed for about 10 years. The women with the highest blood levels of genistein were 65% less likely to develop breast cancer compared to the women with the lowest blood levels of genistein.
It's hard to interpret research on diet and breast cancer risk. This is because the research usually asks people to recall what they ate for a certain period of time. People often don't remember what they've eaten or may be uncomfortable reporting that they ate an entire bag of cookies or a pint of ice cream. The study reviewed here is unique -- instead of asking women what they ate, the researchers simply measured genistein levels.
The researchers aren't sure how genistein might lower breast cancer risk. Genistein and estrogen have similar chemical makeups. So the researchers think that genistein might sit in the estrogen receptors on breast cells and block the cancer-promoting effects of estrogen made by your body. This is how tamoxifen works to lower breast cancer risk and the risk of breast cancer coming back.
The researchers aren't sure if these results will apply to women in Western countries, such as the United States. Japanese women usually eat soybeans and chick peas throughout their lives, starting as young children. Most women in Western countries don't eat soybeans or chickpeas until they're adults. A 2006 research study found that eating soy regularly as a young girl may help protect against the development of breast cancer later on in life.
No food or diet can prevent you from getting breast cancer. But some foods can make your body the healthiest it can be, boost your immune system, and help keep your risk for breast cancer as low as possible. If you think you'd like to change your diet to include more fruits and vegetables, you may want to talk to a registered dietitian about how to create a healthy diet plan that is right for you. Visit the breastcancer.org Nutrition section to learn more about healthy eating and balancing your diet.
NEW YORK (Reuters Health) - Women with high blood levels of an estrogen-like compound found in soy seem to have a lower risk of developing breast cancer, a new study suggests.
Researchers found that among more than 24,000 middle-aged and older Japanese women, those with the highest levels of the compound, called genistein, were only one-third as likely as other women to develop breast cancer over 10 years.
Genistein is one of the major isoflavones, plant compounds found in soybeans, chick peas and other legumes that are structurally similar to the hormone estrogen, and are believed to bind to estrogen receptors on body cells.
While some studies have linked soy consumption with a lower risk of breast cancer, others have found no protective effect. Some animal research, in fact, has suggested that genistein might spur tumor development and growth. The new findings, reported in the Journal of Clinical Oncology, suggest that this is not the case in women, at least when genistein is consumed through food alone.
"This finding suggests a risk-reducing rather than a risk-enhancing effect of isoflavones on breast cancer, even at relatively high concentrations within the range achievable from dietary intake alone," write the researchers, led by Dr. Motoki Iwasaki of the National Cancer Center in Tokyo.
The study included 24,226 women ages 40 to 69 who gave blood samples and completed a dietary assessment, then were followed for an average of 10 years. During that time, 144 women were diagnosed with breast cancer.
When Iwasaki's team separated the women based on their blood levels of genistein at the study's start, they found that the one-quarter with highest levels were 65 percent less likely to develop breast cancer than the quarter of women with the lowest genistein levels.
There was no risk reduction seen among women with moderate levels of the isoflavone, however.
Most past studies on soy isoflavones and breast cancer have used dietary questionnaires, Iwasaki noted. "In contrast, our study used a direct measurement of plasma isoflavone levels, which provides not only an index of intake but also of the absorption and metabolism of isoflavone," the researcher told Reuters Health.
Together with past studies, Iwasaki said, the findings suggest that a high isoflavone intake from food may help lower breast cancer risk.
Whether the findings necessarily extend to women in Western countries is not clear, however. Japanese women, Iwasaki noted, typically consume soy isoflavones on a regular basis starting from a young age, which may influence the compounds' effects on breast cancer development.
SOURCE: Journal of Clinical Oncology, April 1, 2008.
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