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Phytoestrogens

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Updated July 12, 2013

Written or reviewed by a board-certified physician. See About.com's Medical Review Board.

Phytoestrogens are chemicals found naturally in certain plants, including foods like whole grains, leafy greens, beans, and garlic. Scientific research shows that phytoestrogens can mimic the action of estrogen, a hormone that influences functioning in the female reproductive system. In alternative medicine, dietary supplements containing phytoestrogens are sometimes used to protect against hormone-dependent cancers (including some forms of breast cancer), heart disease, osteoporosis, and menopausal symptoms.

Health Benefits of Phytoestrogens

So far, studies on the health effects of phytoestrogens have yielded mixed results. Here's a look at several key study findings:

1) Breast Cancer

Some research shows that women in countries with a high consumption of phytoestrogens may have a lower risk of breast cancer. In a report published in CA: A Cancer Journal for Clinicians in 2007, scientists note that exposure to phytoestrogens in childhood or early adolescence may help protect against future incidence of breast cancer. However, the report's authors found very little human data on the role of phytoestrogens in preventing breast cancer recurrence.

2) Hormone Replacement Therapy

Some women use phytoestrogens as an alternative to hormone replacement therapy (or HRT, a treatment approach used to reduce menopausal symptoms and decrease risk of osteoporosis and cardiovascular disease). For a 2001 research review published in Archives of Internal Medicine, investigators analyzed 74 studies on phytoestrogens and concluded that there isn't enough evidence to recommend the use of phytoestrogens in place of traditional HRT. However, the review's authors note that "evidence for the potential health benefits of phytoestrogens is increasing."

3) Menopause

Phytoestrogens have some beneficial effect on bone mineral density, insulin resistance, and cholesterol levels among women undergoing menopause, according to a review published in Fertility and Sterility in 2007. The review's authors sized up 21 studies, finding no evidence that phytoestrogens can protect against breast cancer, bone fracture, or cardiovascular disease in postmenopausal women.

Sources of Phytoestrogens

Phytoestrogens are present in a number of substances commonly found in dietary supplements, including:

1) Flaxseed

High in fiber and omega-3 fatty acids, flaxseed is a type of phytoestrogen shown to reduce cholesterol levels (especially in postmenopausal women) and cool hot flashes.

2) Soy

Also found to fight hot flashes and lower cholesterol levels, soy contains phytoestrogen compounds called isoflavones. Preliminary research indicates that soy may also help keep bones strong, as well as slightly decrease risk of breast cancer.

3) Red Clover

Another source of isoflavones, red clover is an herb often used to ease menopausal symptoms. This phytoestrogen has been found to tame hot flashes, as well as inhibit the loss of bone mineral density during menopause. Findings from preliminary research also suggest that red clover may reduce prostate cancer risk.

Other sources of phytoestrogens include alfalfa, hops, and vitex.

Using Phytoestrogens for Health Purposes

Use of phytoestrogens has been shown to produce adverse effects in some individuals. For instance, some research suggests that genistein (a phytoestrogen found in soy) may interfere with the actions of tamoxifen (a drug used to treat breast cancer). What's more, people who have (or are at risk for) any type of hormone-sensitive condition may need to avoid phytoestrogens, due to their estrogen-like activity.

If you're considering the use of phytoestrogens in treatment or prevention of any health problem, it's crucial to consult your physician in weighing the potential benefits and risks.

Sources

Al-Azzawi F, Wahab M. "Effectiveness of phytoestrogens in climacteric medicine." Ann N Y Acad Sci. 2010 Sep;1205:262-7. doi: 10.1111/j.1749-6632.2010.05678.x.

Duffy C, Perez K, Partridge A. "Implications of phytoestrogen intake for breast cancer." CA Cancer J Clin. 2007 Sep-Oct;57(5):260-77.

Glazier MG, Bowman MA. "A review of the evidence for the use of phytoestrogens as a replacement for traditional estrogen replacement therapy." Arch Intern Med. 2001 May 14;161(9):1161-72.

Russell L, Hicks GS, Low AK, Shepherd JM, Brown CA. "Phytoestrogens: a viable option?" Am J Med Sci. 2002 Oct;324(4):185-8.

Tempfer CB, Bentz EK, Leodolter S, Tscherne G, Reuss F, Cross HS, Huber JC. "Phytoestrogens in clinical practice: a review of the literature." Fertil Steril. 2007 Jun;87(6):1243-9.

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