Is Hormone Therapy Safe for Breast Cancer?
Many
postmenopausal women are looking for alternatives to hormone therapy,
especially in light of the recent Women's Health Initiative research findings
concerning the risks of combined estrogen and progestin therapy. Of particular
interest are phytoestrogens, which have been gaining popularity due to their
"natural" status, alleged health claims, and availability in a wide
range of foods and supplements.
Phytoestrogens?
Phytoestrogens
are naturally occurring plant compounds that have some similarities to
estradiol, the most potent naturally occurring estrogen. However,
phytoestrogens tend to have weaker effects than most estrogens, are not stored
in the body, and can be easily broken down and eliminated.
Observational
studies have found a lower prevalence of breast cancer, heart disease and hip
fracture rates among people living in places like Southeast Asia, where diets
are typically high in phytoestrogens. In North America, knowledge of these
reported health effects has stimulated great interest in the health benefits of
phytoestrogens. According to the Food and Drug Administration, the sale of soy
foods, a major source of phytoestrogens, has increased dramatically in the past
decade.
Sources
of Phytoestrogens
Phytoestrogens
consist of more than 20 compounds and can be found in more than 300 plants,
such as herbs, grains and fruits. The three main classes of dietary
phytoestrogens are isoflavones, lignans and coumestans:
1. Isoflavones
(genistein, daidzein, glycitein and equol) are primarily found in soy beans and
soy products, chickpeas and other legumes.
2. Lignans
(enterolactone and enterodiol) are found in seeds (primarily flaxseed), cereal
bran, legumes, and alcohol (beer and bourbon).
3. Coumestans
(coumestrol) can be found in alfalfa and clover. Most food sources containing
these compounds typically include more than one class of phytoestrogens.
The Skeletal
Effects of Phytoestrogens
Much of the
evidence concerning the potential role of phytoestrogens in bone health is
based on animal studies. In fact, soybean protein, soy isoflavones, genistein,
daidzein and coumestrol have all been shown to have a protective effect on bone
in animals who had their ovaries surgically removed.
In humans,
however, the evidence is conflicting. Compared to Caucasian populations,
documented hip fracture rates are lower in countries such as Hong Kong, China
and Japan where dietary phytoestrogen intakes are high. Yet reports suggest
that Japanese women have a greater risk of sustaining a vertebral fracture than
Caucasian women.
The Risks and
Benefits
Some studies
suggest that, unlike estrogen, phytoestrogens do not appear to target breast or
uterine tissue. This suggests that they may act more like SERMS (selective
estrogen receptor modulators such as raloxifene and tamoxifen) than actual
estrogens. However, in other studies high isoflavone levels have been linked to
an increased risk of breast cancer.
Clearly,
additional research is needed to further evaluate the effects of phytoestrogens
before judgments regarding their safety and usefulness can be made.
Key Points
Based on
information available at this time, it is reasonable to make the following
conclusions concerning phytoestrogens and bone health in postmenopausal women:
1. Moderate
amounts of foods containing phytoestrogens can be safely included in the diet
but do not expect it to help build bone. Keep to the basic rule - eat the least
processed forms.
2. Due to a lack
of evidence and concerns about safety, supplementation with synthetic
isoflavones (ipriflavone) is in question.
3.
Postmenopausal women are encouraged to view evidence concerning phytoestrogens
and bone health as conflicting and incomplete. For women who are estrogen
dominant increasing their phytoestrogen intake may not improve their bone
position.
Several studies have explored the effects of soy isoflavones on bone health, but results have been mixed, ranging from a modest impact to no effect. Most of these studies have serious limitations, including their short duration and small sample size, making it difficult to fully evaluate the impact of these compounds on bone health.
Several studies have explored the effects of soy isoflavones on bone health, but results have been mixed, ranging from a modest impact to no effect. Most of these studies have serious limitations, including their short duration and small sample size, making it difficult to fully evaluate the impact of these compounds on bone health.
