Fact Sheets – The Facts about Estrogen

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What is estrogen?

Estrogen is a natural female hormone produced by the ovaries in women and the testes in men. Estrogen is found in much higher concentrations in women’s bodies. It stimulates puberty, regulates the menstrual cycle and breast development, plays a crucial role in pregnancy, and is also necessary to maintain strong, healthy bones. The level of estrogen present in a woman’s body varies depending on her age and monthly cycle. During certain times of the month, estrogen levels are higher or lower. Estrogen levels decrease dramatically after menopause, which can cause thinning of the bones or osteoporosis. In addition to the estrogen produced by their own ovaries, many women are exposed to synthetic or man-made estrogens through oral contraceptive (birth control) pills (OCs), transdermal patches, hormone replacement therapy (HRT), and vaginal creams and rings. The two most common medical uses for synthetic estrogens are birth control and hormone replacement therapy taken after menopause.

What are estrogen-mimicking compounds?

Some substances contain compounds that are structurally similar to estrogen on a molecular level. One type, phytoestrogens, is naturally occurring and found in plants. Other substances in the environment, including some chemicals, have estrogen-like properties and are considered estrogen mimickers. These compounds can have estrogen-like effects on plants and animals, including humans. Currently, there is a significant research effort to determine the health effects of estrogen-mimicking compounds, especially in terms of reproductive outcomes and cancer risk.

Does estrogen cause cancer?

Research has linked estrogen to cancers of the breast, endometrium (uterus), and cervix. Known risk factors for breast cancer include conditions that cause women to be exposed to higher estrogen levels over their lifetimes, such as early menarche (beginning of the monthly period at a young age), late menopause, having children after age 30 or having no children. Findings from research studies attempting to link oral contraceptives containing estrogen to breast cancer have not yielded clear results. Some studies show an association, while others do not. On the other hand, the Women’s Health Initiative showed a clear increase in breast cancer in women who took combined HRT (estrogen and progestin). It is not clear whether women who take estrogen replacement therapy (estrogen alone without progestin) have a higher risk as well, although it appears they do not. Scientific studies have consistently and clearly shown that prolonged estrogen exposure increases the risk of endometrial (uterine) cancer. According to some studies, long-term use of oral contraceptives containing estrogen may increase the risk of cervical cancer. Oral contraceptives may also increase the risk of certain malignant liver tumors and are known to cause hepatic adenomas, rare but benign liver tumors that do not spread but can cause bleeding. Conversely, studies have revealed that taking oral contraceptives actually reduces the risk of ovarian cancer.

What is the Women’s Health Initiative (WHI)?

The Women’s Health Initiative is a large study of 16,000 women ages 50 through 79, which revealed that women on HRT ran a higher risk of heart disease, stroke, breast cancer, and blood clots. The study was stopped in July 2002 when researchers realized that combined HRT (estrogen and progestin) had significantly more risks than benefits. Based on these findings, doctors no longer recommend HRT as the primary form of prevention and treatment of osteoporosis or post-menopausal symptoms.

Should I stop taking birth control pills or HRT?

If you are concerned about taking products containing estrogen, consult with your physician. The decision should be made based on a thorough review of your personal and family medical histories and what risk factors you have for cancers of the breast, uterus, and cervix. Your personal and family history of heart disease and stroke must also be considered, since recent research clearly shows that HRT increases the risk of cardiovascular disease. Deciding to take OCs or HRT is a personal as well as a medical decision. For many women, the need for birth control or regulation of the menstrual cycle may outweigh the potential risks of taking oral contraceptives. Some women have such severe menopausal symptoms that they may choose to take HRT as a short-term treatment. Long-term administration of HRT, as in the prevention and treatment of osteoporosis, is not recommended primarily due to the increased risk of cardiovascular disease. As always, any medical decision should be made after a thorough discussion with a physician where the risks and benefits based on an individual’s personal situation are fully explained.

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