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estrogens and breast cancer: Researcher offers overview
Diana Yates, Life
photo to enlarge
by L. Brian Stauffer
Helferich, a professor of food science and human
nutrition, has spent a decade evaluating the health
effects of isoflavones, a class of plant estrogens
present in high concentrations in soy.
CHAMPAIGN, Ill. —
Are soy products healthy additions to a person’s diet, safe alternatives
to hormone-replacement therapy or cancer-causing agents? The answer,
according to University of Illinois food
science and human nutrition professor William Helferich, is, “It
He reviews the science linking breast cancer, soy and dietary supplements
that contain soy phytoestrogens this month at a conference on “Diet
and Optimum Health” sponsored by the Linus Pauling Institute at
Oregon State University.
Helferich has spent a decade evaluating the health effects of isoflavones,
a class of plant estrogens present in high concentrations in soy. Much
of his work has focused on a single isoflavone, genistein, which occurs
in varying concentrations in soy products or ingredients such as tofu,
soy protein isolates, soy flour and some estrogenic dietary supplements.
Genistein is of interest because it is the most active of the soy isoflavones,
and because it activates estrogen receptors in cells, including some
breast tumor cells.
Dozens of studies of the role of human and plant estrogens in breast
cancer have yielded seemingly contradictory findings. Some found that
feeding genistein to female rats prior to puberty reduced the number
of chemically induced mammary tumors. Other studies showed that estradiol,
a primary human estrogen, spurs the growth of existing estrogen-dependent
Helferich and colleagues demonstrated that – like estradiol –
dietary genistein stimulates the growth of estrogen-responsive tumors.
They also found that dietary genistein interferes with treatments, such
as tamoxifen, that target estrogen receptors in breast tumors. (About
70 percent of women with breast cancer have estrogen-responsive tumors.)
“The resolution of this paradox may lie in the timing of estrogen
administration,” Helferich said. Exposure to genistein, an estrogen,
before puberty causes mammary gland differentiation. “A differentiated
cell undergoes less proliferation and therefore is less likely to progress
through the cancer process,” he said. “However, if the estrogen
is administered to an animal after the development of an estrogen-responsive
tumor, the growth of this tumor will be stimulated,” he said.
Today Helferich is most concerned about the use of genistein and other
isoflavones in supplements sold as “natural” alternatives
to hormone-replacement therapy. He notes that midlife women who consume
these products perceive them as natural and safe. But women aged 50
and older are also most at risk of developing breast cancer. Helferich
is evaluating the biological activity of some of these products, which
are available in many forms, do not require a prescription, and in most
cases are consumed without the knowledge of their physicians.
Helferich notes that the incidence rate of breast cancer in women aged
50 and over in the U.S. dropped significantly after use of hormone-replacement
therapy (HRT) declined in 2002 and 2003. While purified genistein is
not as potent as HRT, Helferich said, it still poses a risk to midlife
women because the amount consumed is much higher. The labels of many
products that contain this and other isoflavones lack vital information
about what is actually in their products, he said, and because these
are natural products, the consistency from batch to batch is difficult
“Women are participating in an ongoing experiment with an unknown
outcome,” he said. “You can’t identify what dose of
isoflavones you’re getting.”
But genistein is only one component of soy, Helferich said, and studying
its effects in purified form may lead to misleading conclusions about
the health consequences of soy in the diet. In fact, studies have shown
that foods like soy flour have a very different effect.
“The complex mixture found in soy flour doesn’t make the
tumor grow,” Helferich said.
“Whole soy contains a lot of biologically active ingredients,
but together they may have multiple effects that can reduce the negative
outcomes. When the whole food is consumed you get a very different effect
than if you consume the concentrated constituents individually.”
All this research points to a very simple truth, Helferich said: The
whole soybean is healthier than many of its individual chemical parts.
“That raw food can be consumed for less than a dollar a serving
and is likely better for you than that thing you pick up at the health
food store for $30 a pound,” he said.
Editor’s note: To reach William Helferich,
call 217-244-5414; e-mail: firstname.lastname@example.org.