PhytoEstrogens . . . .
are estrogen-like chemicals found in plant foods such as beans, seeds, and grains.
Foods made from soybeans have some of the highest levels of phytoestrogens
and have been studied the most.
Phytoestrogens and Breast Cancer
Fact Sheet #01, revised July 2001
Phytoestrogens are estrogen-like chemicals found in plant foods such as beans, seeds, and grains. Foods made from soybeans have some of the highest levels of phytoestrogens and have been studied the most. In spite of initial optimism, it is not clear whether eating foods rich in phytoestrogens decreases breast cancer risk. This is an active area of research with much work needed to resolve this issue. This fact sheet presents the most current information and indicates where more research would be helpful.
What are phytoestrogens?
Phytoestrogens are a group of chemicals found in plants that can act like the hormoneestrogen. Estrogen is a hormone necessary for childbearing and is involved with bone and heart health in women. However, higher exposure to estrogens over a lifetime is linked with increased breast cancer risk. (See BCERF Fact Sheet #10, What Factors Might Affect a Woman's Exposure to Estrogen).
What foods contain phytoestrogens?
More than 300 foods have been shown to contain phytoestrogens. Most food phytoestrogens are from one of three chemical classes, the isoflavonoids, the lignansor the coumestans. Isoflavonoid phytoestrogens are found in beans from the legume family; soybeans and soy products are the major dietary source of this type of phytoestrogens. Lignan phytoestrogens are found in high fiber foods such as cereal brans and beans; flaxseeds contain large amounts of lignans. The coumestan phytoestrogens are found in various beans such as split peas, pinto beans, and lima beans; alfalfa and clover sprouts are the foods with the highest amounts of coumestans.
Can phytoestrogens from soy foods affect breast cancer risk?
It is currently unclear whether phytoestrogens from soy foods affect breast cancer risk. Studies looking directly at breast cancer risk and soy in the diet are not in agreement. Almost half of the studies have reported no effect of soy on breast cancer risk. In addition, animal and cellular studies of soy phytoestrogens have generated both enthusiasm and concern. Animal studies have shown that soy phytoestrogens can decrease breast cancer formation in rats. However, animal and human studies suggest that soy phytoestrogens can behave like estrogen and potentially increase breast cancer risk. Some scientists have suggested that women should be cautious about eating large amounts of the soy products or soy supplements, because of the possible harmful effects of soy phytoestrogens. These concerns and areas of research are discussed below in more detail.
How do phytoestrogens act in the body?
There are many different ways that phytoestrogens may work in the body. The chemical structure of phytoestrogens is similar to estrogen, and they may act as mimics (copies) of estrogen. On the other hand, phytoestrogens also have effects that are different from those of estrogen.
Working as estrogen mimics, phytoestrogens may either have the same effects as estrogen or block estrogen's effects. Which effect the phytoestrogen produces can depend on the dose of the phytoestrogen. The phytoestrogen can act like estrogen at low doses but block estrogen at high doses. Estrogen activates a family of proteins called estrogen receptors. Recent studies have shown that phytoestrogens interact more with some members of the estrogen receptor family, but more information is needed about how these receptors work, especially in breast cancer. Finally, phytoestrogens acting as estrogen mimics may affect the production and/or the breakdown of estrogen by the body, as well as the levels of estrogen carried in the bloodstream.
Phytoestrogens - acting differently from estrogen - may affect communication pathways between cells, prevent the formation of blood vessels to tumors or alter processes involved in the processing of DNA for cell multiplication. Which of these effects occur is unknown. It is very possible that more than one of them may be working. Also, the effects in various parts of the body may be different.
What have human studies on soy in the diet and breast cancer risk found?
The results of the case-control human studies of the connection between eating soy products and breast cancer risk are conflicting. Some studies have reported no link and others have reported a decrease in the risk of breast cancer among women eating soy compared to women who did not eat soy; no studies have reliably demonstrated an increase in the risk of breast cancer among women eating soy. In addition to the conflicting results, there are four problems with these studies. First, the number of studies is small, only ten studies have examined soy in the diet and breast cancer risk. Second, most of the studies examined small numbers of women, only four of the studies included more than 200 patients. Third, all but two of the studies were limited to women from Asia. The effect of soy in Asian women may not best reflect much of the population of Western countries like the US. Women in Asia differ in important ways. Many of them have eaten soy products all their lives and their usual diets contain large amounts of soy products. Also, Asian women have low rates of breast cancer compared to Western women, which may be related to other factors besides soy in their diet. Fourth, most of these studies are limited by their focus on the general diet of women rather than soy products in detail. More carefully controlled studies are needed that examine the effect of soy products on breast cancer risk in women from cultures outside of Asia and more indepth studies are needed of Asian women.
What is the effect of eating soy on women's hormone levels and growth within the breast?
Soy phytoestrogens could change breast cancer risk by changing the production and/or breakdown of reproductive hormones such as estrogen. The results of studies examining hormone changes among women eating soy have not been consistent, but recent studies suggest there may be a small decrease in the levels of estrogens in the body. Some studies have also shown that eating soy phytoestrogens is associated with a decrease in the formation of forms of estrogens that may directly lead to cancer causing mutations.
One of the ways higher estrogen exposure may be linked to breast cancer risk is through its ability to increase growth of milk ducts in the breast. Most breast cancer arises from these ducts. Several but not all studies examining the effect of soyphytoestrogens on breast growth in women have suggested that phytoestrogens have a weak estrogen-like effect. The longest examination followed 28 women for a year. These women received a soy supplement for six months. While they were taking this supplement the women were found to have more growth of the milk ducts in their breasts. These studies are not conclusive, but such growth could increase breast cancer risk. More study is needed to evaluate the possible effects of soy phytoestrogens on growth within the breast and hormone levels in the body.
What are the results of the animal and cellular studies examining soy phytoestrogens and breast cancer?
Animals that were given soy phytoestrogens developed fewer mammary (breast) tumors in many, but not all, studies. The decrease in tumor formation was dependent on the age at which the animals were given the soy. Animals given a soy phytoestrogen before sexual maturity had about half as many tumors as animals given a soy phytoestrogen as adults. A similar effect of the age of treatment was also seen when animals were given a synthetic estrogen or estrogen together withprogesterone. More studies are needed to understand this effect of phytoestrogens and of estrogen itself.
Studies of breast cells in tissue culture have shown that soy phytoestrogens can either encourage or discourage growth within the breast. This effect depends on the amount of the soy phytoestrogen the cells are exposed to (See "How do phytoestrogens act in the body?" below). It is unclear if these effects on cells in the laboratory are the same or different from breast cells in the body.
Have other classes of phytoestrogens been examined for their effect on breast cancer risk?
Both lignan (from brans, beans, and seeds) and coumestans phytoestrogens (from beans and sprouts) have been studied for a possible effect on breast cancer risk. Two studies have found higher levels of lignan phytoestrogens in the urine of women who may be at lower risk for breast cancer, such as Japanese women and women eating a macrobiotic diet. Other studies compared women without cancer to women with breast cancer; the women with breast cancer had significantly lower levels of lignan phytoestrogens in their urine. Phytoestrogen levels in urine are an accurate measure of phytoestrogens in the body, but it is uncertain how levels in the women with cancer compare to levels in these women during the decades when cancer was developing.
A lignan phytoestrogen found in flaxseed, secoisolariciresinol diglycoside (SDG) has been shown to interfere with mammary (breast) tumor formation in rats. SDG has similar effects on the development of mammary gland as the soy phytoestrogengenistein. (But see the discussion of potential SDG/flaxseed toxicity in the question on pregnancy and nursing below.)
Coumestans are the least studied phytoestrogens. Treatment of rats with a coumestan phytoestrogen had no effect on mammary (breast) tumor formation but this phytoestrogen has been examined in only one study of this type. Some coumestans have strong interactions with estrogen receptors. This makes them like the strongestestrogens made by the body and suggests that they may also have estrogen-like actions.
Is there any harm in taking phytoestrogen supplements or eating large amounts of foods with phytoestrogens?
Care should be taken in the use of phytoestrogen supplements that may contain phytoestrogens at levels far higher than in food. Since phytoestrogens can haveestrogen-like effects in humans, use of these supplements for a long time could increase breast cancer risk.
Moderate consumption of foods high in phytoestrogens is unlikely to have any adverse effects and these foods are generally healthful.
Is there a certain time during a woman's life when eating phytoestrogens can be of the greatest benefit?
One recent study of Chinese women suggests that eating large amounts of soy during adolescence may reduce the risk of breast cancer. Studies in animals have demonstrated that the period of breast development is critical for mammary tumor inhibition by phytoestrogens. It is currently unclear if the results in Chinese women reflect a similar critical period or a lifetime of eating soy products.
Human epidemiological studies suggest that if breast cancer risk reduction is linked to eating soy phytoestrogens, the effect may be greater on premenopausal breast cancer. More studies are needed to determine if soy phytoestrogen and other phytoestrogens act largely on premenopausal breast cancer and whether the effectiveness of phytoestrogens is related to the period of life when they are eaten.
Should breast cancer survivors eat more phytoestrogens?
No studies have examined the health effects of eating phytoestrogens among breast cancer survivors. Drugs or chemicals that cause growth of breast tissue are generally not recommended for breast cancer survivors. Phytoestrogen supplements have been shown to cause growth of breast tissue in animals and healthy women.
No human studies have assessed the effects of combining tamoxifen (an anti-estrogenic drug prescribed for many breast cancer survivors and some women at high risk for breast cancer) and phytoestrogens in breast cancer survivors. Women taking tamoxifen are usually not included in studies where concentrated supplements of phytoestrogens are given. Studies examining the actions of tamoxifen and genistein in the laboratory using isolated breast cancer cells have produced conflicting results. In some studies the two chemicals acted together, and in others their effects were opposing. More studies are needed to understand potential favorable or conflicting actions between these two chemicals.
Should I eat more phytoestrogens if I am taking estrogen for treatments such as birth control or postmenopausal hormone therapy?
The effects of phytoestrogens on women taking birth control pills or being treated withpostmenopausal hormonal therapy have not been examined. Both of these treatments use estrogen, and since phytoestrogens can act like the hormone estrogen, phytoestrogens might disrupt or amplify the effect of the estrogen in individuals with a diet very high in phytoestrogens. However, such effects have not been reported in groups of women who have diets high in phytoestrogens.
Should infants and young children eat phytoestrogens?
The regulatory bodies of several countries, including Great Britain, Switzerland, Australia, and New Zealand, have suggested that soy infant formulas be used only in children who are not breast fed and are definitely intolerant to cow's milk. Soy formulas contain much higher amounts of phytoestrogens than is seen in human breast milk. In addition, infants fed soy formula have blood levels of phytoestrogens that are far greater than normal levels of estrogen in infants. No studies have examined the health effects of children eating phytoestrogen-rich foods. Long-term studies that look at the health benefits and risks of soy-based infant formulas and eating phytoestrogen-rich foods as a child are needed.
Should I eat phytoestrogens if I am pregnant or breast-feeding?
Pregnant or breast-feeding women should not use phytoestrogen supplements or consume substantial amounts of flaxseeds on a regular basis. In animal studies, the phytoestrogens found in high amounts in flaxseeds have been shown to cause developmental abnormalities and some studies of soy phytoestrogens have shown a possible increase in susceptibility to cancer in offspring. Eating moderate amounts of soy or flax products should present no problem. Women in China and Japan regularly eat foods containing soy phytoestrogens during pregnancy and while breast-feeding and no adverse health affects have been reported in these countries.
Do phytoestrogens have other health benefits?
Phytoestrogens are actively being researched for beneficial effects on cardiovascular and bone health. Studies are also examining various phytoestrogens for relieving some of the symptoms associated with menopause.
What can women do now?
It is unclear what role foods containing phytoestrogens play in decreasing breast cancer risk. Women can help themselves stay healthy by eating plenty of fruits, vegetables, whole grains, and beans and by getting plenty of exercise and maintaining a healthy weight.
What scientific studies need to be done?
The following aspects of phytoestrogens especially need further study:
Effects of phytoestrogens, especially from soy, on breast cancer risk in humans
Actions of soy phytoestrogens on breast development in humans
Health effects of soy phytoestrogens on individuals who used soy formula as an infant
Consequences of phytoestrogens on breast cancer survival
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Prepared by Barbour S. Warren, Research Associate, BCERF &
Carol Devine, Ph.D., R.D., Educational Project Leader, BCERF
More Research on Estrogens and their effect on
Breast Cancer and Uterine Imbalances - FYI
Herbs and Supplements with Estrogen Action Q&A
[Dalene Barton, CH, Doula]
Dalene Barton, CH, Doula
Below are some of the most common questions about estrogen action of herbs and supplements we get from our subscribers, visitors, and community. The estrogen-like action of herbs and supplements can be very confusing. The intention of this Q&A is to help dispel any of the confusion, but it may also raise more questions. Please feel free to post your questions and comments below this article! We value healthy discussion and would love your feedback!
Q: My doctor tested my hormone levels, he says I have estrogen dominance. Is Red Clover, Licorice rt. and Royal Jelly okay to take? Will these increase my estrogen? Should I avoid them completely?
A: Through my learning and research I have come to find that herbs and supplements that contain phytoestrogens, or have the propensity to mimic estrogen may protect our bodies from estrogen dominance. Though not all natural health care practitioners may agree, most do. The reason is because of xenoestrogens. Xenoestrogens come from human-made chemicals like plastics, pesticides, paint, body care products, ect. These are ingested, breathed, or slathered onto our skin daily. Xenoestrogens are endocrine disruptors. These chemicals have the ability to interfere with the natural functions and development of our bodies. The main function of the endocrine system is to serve as our body’s message center. Hormones deliver messages, the endocrine system coordinates hormones.
Xenoestrogens have the ability to bind to our estrogen receptor sites; disrupting the function of the endocrine system. Not only can they mimic our natural hormones, but they can block other hormones from binding to receptor sites. Xenoestrogens elicit a very strong estrogenic action. All xenohormones are endocrine disruptors. They can alter how natural hormones are produced, metabolized and eliminated.
A person who consumes a diet rich in phytoestrogens may be more likely to protect their body from xenoestrogens. Phytoestrogens eaten daily may bind to receptor sites first, blocking the xenoestrogens from binding. Plus, phytoestrogens elicit a weaker estrogenic effect than xenoestrogens.
Red Clover, Licorice rt. and Royal Jelly have all been found to have the propensity to mimic estrogen in the body, but they also have superior nutritional benefits as well. The superior health benefits of these 3 outweigh any concern for increasing estrogen in the body. They may actually protect our bodies from xenoestrogens. To actually increase estrogen levels, they would need to be consumed in very large concentrated amounts, over a long period of time, which is not recommended. Herbalists and most natural health care practitioners would not use phytoestrogens in concentrated forms, especially if their patient has an estrogen dominant condition.
Q: I heard that because Red Clover has an estrogenic action it is not safe for pregnancy. Should I avoid it if I think I am pregnant or during my pregnancy?
A: This is going to depend on who you ask. I was recently at an herbal conference and this exact question came up. I was sitting in a room of about 45 female herbalists, when this question was asked, they all agreed they suggest it not be used until the last trimester of pregnancy. Yet all of the herbalists who are mothers admitted they used it for most of their pregnancies, with no adverse reaction. Many clinical herbalists said they have never had a single pregnant mama or baby have any adverse reaction when red clover was suggested.
I have used it for pregnancy preparation, through the last trimester of pregnancy, and during breastfeeding both of my children. I never used concentrated amounts long term. I always use this herb as I would a nourishing food. Red Clover blends well in an infusion with other nourishing herbs like nettles and red raspberry leaf. Because it is detoxifying for the liver and kidneys, I have used it in the childbearing year, and after to aid my body in recovery postpartum. It is extremely hard on the liver, heart and kidneys to develop another human life inside of the female body. Using Red Clover infusion from time-to-time aids the body in proper function of the liver, heart and kidneys, which is essential to a healthy pregnancy.
In all of my research and use I have never seen Red Clover infusion elicit an estrogenic effect on a pregnant mother. You would never want to use a cream made of Red Clover Isoflavone, which is a concentrated form and may increase estrogen in the body.
Q: I consume flax oil daily, but I heard it contains estrogen. Will this cause my body to become estrogen dominant?
A: Flax seeds contain lignans, which are the second strongest group of phyoestrogens, isoflavones being first. It is important to understand that plants that contain phytoestrogens are not the same as our natural endogenous estrogens, which are steroid hormones. Phytoestrogens are chemical constituents in plants. Flax is very high in lignans, as well as fiber. When bacteria in the digestive tract acts on the lignans they are converted into phytoestrogen. Lignans have been found to be anti-estrogenic on estrogen receptor–positive breast cancer.** It is thought that lignans boost production of a substance that fastens on to human estrogen and then it is carried out of our bodies via urination. We do know that the high fiber and lignan content of flax helps to remove excess bad estrogens from the body. Lignans also help prevent healthy cells from free radical attack.
Studies have shown high levels of estrogen in the urine of people that consume flax daily. This shows the ability of flax to remove excess estrogen from the body, while promoting healthy digestion and balanced estrogen levels. Flax oil is also an extremely healthy source of omega 3 fatty acid. Omega 3’s have been shown to aid the body in hormonal balance, production of healthy cervical mucous, and healthy blood flow.
So, to make a long story short, no, there is no evidence that flax oil is going to make your body estrogen dominant. In order for flax seeds to be beneficial they must be ground, or in oil form. The body cannot digest whole flax seeds, they will pass through the digestive system unused, if eaten whole.
Q: I was diagnosed with low estrogen. I have read on other sites that using soy isoflavones in the first half of your cycle will stimulate ovulation and boost my estrogen levels. I am considering using a soy isoflavone supplement to boost my estrogen levels, but is that safe or a good idea?
A: The soy debate may be one of the hottest topics concerning fertility today. Soy contains isoflavones, and has the most concentrated levels of isoflavones of any plant that is consumed by humans. Honestly I feel that soy used in any form that is concentrated may cause estrogen dominance. This is because for one, soy already contains high amounts of isoflavones. Second, soy producuts, including soy isoflavone creams and pills contain even more concentrated levels of isoflavones. This is because of the way these creams and pills are made. Isoflavones from soy beans are chemically isolated in a laboratory, they are then concentrated to make soy isoflavone supplements. These supplements contain more isoflavones than natural soy beans, or whole soy foods.
The goal should not be to manipulate a specific hormone in the body. Supporting and nourishing the systems that produce and control hormones is best. You can do this through good nutrition, herbs, supplements and natural therapies. I have seen time and time again, women really mess up their natural cycles using soy isoflavone supplements. If you choose to use a soy isoflavone supplement, it would be best to do so under the supervision of a health care professional, who can also do regular hormone testing. This would enable you to determine if this product would be right for you.
It is also important to consider why you have low estrogen to begin with. The hormonal system is an intricate system of communication. If something in that system is not functioning properly, a hormone level may drop, or increase to unbalanced levels. The main function of the endocrine system is to serve as our body’s message center. Hormones deliver messages, the endocrine system coordinates hormones. So if a hormone level is out of balance, it may be signaling a problem with a part of the reproductive system; like egg health for example. Healthy follicle (follicles contain eggs) and adequate follicle count is essential for release of the hormone estrogen. Adding estrogen to the body does not solve the problem if a system of the body is malfunctioning, especially in the case of estrogen.
It is important to have clear communication with your doctor about your specific hormone test results. Ask your doctor why he/she thinks your estrogen levels are so low, what may be causing this in your case? Having the answer to that may guide you in the right direction to healing the problem.
Q: I have both endometriosis and uterine fibroids. I take Royal Jelly daily and have felt amazing results from it. My question is, I read the other day that Royal Jelly has the propensity to mimic estrogen, is this true and should I stop using it, since I have estrogen dominant fertility issues?
A: The answer to this may lie in what type ofRoyal Jelly supplement you are taking. If you are using Royal Jelly alone in a capsule form, you may want to consider the research before choosing it.
You would have to consume a lot of Royal Jelly for it to increase your estrogen levels. A study done in Japan on rats, published in 2007, shows that Royal Jelly has the propensity to mimic estrogen. This study also showed the potential for increased size of uterine cells in the rats studied. What I have learned from studies where humans use mice or rats, is that scientists often inject very high, concentrated doses into the rats. This is not how a human would consume a supplement, usually. Because of this, it is hard to determine the true outcome of a study, when considering we are human, not rats. Because endometriosis and uterine fibroids are both disorders with uterine cells, there is a slight concern that Royal Jelly may increase uterine cells, which may not be good for these conditions.
In contrast, Royal Jelly has been found to be extremely nourishing to the endocrine system, aiding in hormonal balance, egg health, decrease in inflammation and boosting of the immune system. These benefits may actually aid the body in healing of endometriosis and uterine fibroids.
Royal Jelly supplements are often sold in a liquid form combined the bee pollen and bee propolis, like the Alive Bee Power Royal Jelly we sell in our Natural Fertility Shop. Bee propolis has been found to be extremely beneficial for women with endometriosis.
A study published in Fertility and Sterility (2003;80:S32) showed that 60% of women with endometriosis related infertility, who took 500mg of bee propolis twice a day for 9 months became pregnant, as opposed to 20% in the placebo group. Endometriosis pain, scar tissue and adhesion formation is thought to be triggered by inflammation response. Bee propolis has been shown to be extremely anti-inflammatory which may reduce endometriosis.
Based on the above information, I would have to say the benefits of Royal Jelly for healing hormonal imbalance, and fertility issues where inflammation is present, gives hope. When we choose to consume super foods like Royal Jelly, we are choosing to nourish and heal the body. I have never had anyone report, nor have I heard of any reports of Royal Jelly exacerbating endometriosis or uterine fibroids.
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