Phytoestrogens
Phytoestrogens:
A woman’s alternative to
estrogen therapy
Pamela Dull, M.D., Mary Jo Welker, M.D., Diane Orlov, R.N., M.S., C.N.P.,
and Danell J. Haines, Ph.D. 2000. Family Practice Recertification, 22(15):58-71.
Reviewer’s Note: The use of phytoestrogens for prevention and potential
treatment of various forms of cancer, reduction of menopausal symptoms,
and as a substitute for hormone replacement therapy may be one of the
most important contributions that botanicals can make to American health,
especially for women. The article described in this review was established
and approved as a continuing education module for health care professionals.
It addresses the current state of knowledge of these compounds.
This article focuses on the potential use of phytoestrogens for menopausal
women. There are approximately 42 million women in America over the
age of 50. By 2010 this number will increase to 52 million. It is estimated
that at least 85% of these women are already experiencing menopausal
symptoms associated with a decline in circulating estrogen. These symptoms
include: hot flashes, night sweats, insomnia, memory loss, and vaginal
dryness.
Conventional treatment of menopausal symptoms focuses on two primary
therapeutic outcomes: management of symptoms and prevention of related
conditions, most notably, heart disease and loss of bone density (estrogen
plays a key role in both). The primary therapy applied is hormone replacement
therapy (HRT). However, it is estimated that only 20% of eligible women
are prescribed HRT and that, in the first year, 50% of those taking
HRT discontinue its use. A large percentage of women who were surveyed
reported they used various other treatments to counter the effects of
menopause, including nutritional and herbal supplements (such as calcium
and multi-vitamins), exercise, weight management, and, most popularly,
soy products.
Postmenopausal
Estrogen Therapy—The Risks
While estrogen replacement
therapy can reduce symptoms associated with menopause, it is also associated
with an increased risk of many conditions, including breast and endometrial
cancer, venous thrombosis (blood clotting that can lead to heart attack
or stroke), gall bladder disease, high blood pressure, intermittent
vaginal bleeding, and depression, to name a few. Approximately 10% of
women have conditions in which HRT is inappropriate, such as a history
of estrogen-dependent cancers (many forms of breast cancer). It is pointed
out that the increased risk of cancer associated with HRT is due to
relatively high levels of unopposed estrogens. The combination of progesterone
and estrogen has gained in popularity to help minimize these risks.
However, in a study of 46,355 postmenopausal women, those who took the
combination therapy were observed to have an increased risk of breast
cancer over those who took estrogen alone.
Phytoestrogens
Many women believe
that phytoestrogens offer a safe, effective, and inexpensive self-help
method for addressing menopausal symptoms. This belief is correlated
with the general increased interest in alternative medicine in recent
years. Phytoestrogens are defined as plant-derived non-steroidal compounds
with a structure that is similar to estrogen. This structural similarity
causes them to bind to estrogen receptor sites that would otherwise
be occupied by true estrogen. It is this “competitive” action
that is partly responsible for the benefits of phytoestrogens. Phytoestrogens
act in a manner that is either similar or exactly the same as true estrogen.
However, they are reportedly 100-1,000 times weaker in activity. In
premenopausal women, the effects of phytoestrogens may be minimal due
to their weak action. However, after normal estrogen levels have fallen,
the effects of increased amounts of weak phytoestrogens may be more
clinically relevant. The most common and widely studied of the phytoestrogens
are genistein and daidzein, two compounds found in soy.
Phytoestrogen
Research
Interest in phytoestrogens,
and specifically in soy, came from reviews of the typical Japanese diet,
which delivers approximately 40-80 mg per day of isoflavones, a particular
group of phytoestrogens. Soy consumption in Japan was reported to be
correlated with much lower rates of breast and other reproductive cancers
than are typical among Americans. Moreover, it was found that the rate
of breast cancer in Japanese women who moved to America and adopted
American eating habits increased to meet the relative national average
typical of Americans. Decreased consumption of soy and increased consumption
of animal fats have been two of the primary dietary habits correlated
with this change. Asian women similarly have a much lower incidence
of menopausal symptoms, osteoporosis, cardiovascular disease, and uterine
cancer. While other factors, such as less fat consumption, greater consumption
of vegetables, and more exercise must be taken into consideration, soy
has been the focus of much of these health benefits.
In one study of 104 post-menopausal women, 60 g per day of soy protein
was significantly more effective than placebo for reducing hot flashes.
In another study of 66 post-menopausal women, increased consumption
of isoflavones (amount not disclosed) was correlated with increased
mineralization of the lumbar spine. Specifically, an isoflavone known
as ipriflavone was found to decrease bone resorption, increase osteoblast
function, reduce bone fractures, and decrease bone pain. Other epidemiological
(population) studies show that increased consumption of soy isoflavones
is correlated with a decreased risk of heart disease in post-menopausal
women, with heart disease 75% less prevalent in Japanese women than
in American women. The cardiovascular protective effects of soy have
been correlated with its potential antioxidant and anti-thrombotic activity.
Soy has also been shown to lower cholesterol.
With regard to cancer, Japanese women’s risk of breast cancer is
4 times lower than that of American women, while the incidence of endometrial
cancer is 10 times lower than in American women. In addition, women
in Japan who do get cancer have fewer nodules and less metastasis (spread)
than women in the U.S. and England. One case-controlled trial in Australia
reported that a high intake of phytoestrogens, in the form of legumes
and fiber, substantially reduced the risk of breast cancer.
Conclusions
Not Definitive
This article points out that the evidence for the health benefits of
soy is not definitive and there is still much to learn about the role
soy should play in medical care. While acknowledging soy’s many
benefits, such as reduced risk of heart disease, lowering of cholesterol,
and reduced risk of cancer, they further comment that some within the
medical establishment have concerns that the “estrogenic”
nature of soy may not be appropriate for some people and that it may
not be effective for treating post-menopausal vaginal dryness. The authors
also point out that there is insufficient information as to whether
soy supplements are equivalent in action to whole soy foods. They conclude
that all women should be able to make educated choices based on accurate
information as to the direction they should take in managing their own
menopausal symptoms.
Primary Food Sources of Phytoestrogens
Soybeans Miso
and Soy Products Soy cheese
Soy flour
Soy meal
Soy milk
Tempeh
Tofu
Lignans Flax seed (oil/meal/flour)
Cereals and brans
Seeds rich in oils (soy, sunflower, peanut)
Legumes (lentils, beans)
Vegetables (asparagus, broccoli, carrots)
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