The Isoflavone Genistein From Soybean May Prevent Breast Cancer

Women with high blood levels of an anti-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.

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.