Estrogen Types and Their Connection to Breast Cancer

Estrogen, a hormone that controls many aspects of female physiology, can be associated with breast cancer. The body naturally makes a few different estrogen compounds, and the production and release of each type of estrogen fluctuate during phases of puberty, menstruation, pregnancy, and menopause.

Women (and men) can be exposed to other types of estrogen as well. Synthetic estrogens are used in medication. Plant-based estrogens are sometimes used in supplements. Xenoestrogens are a byproduct of commercial chemical compounds and can enter the body through contamination.

Each estrogen type may impact breast cancer differently, but often, the effects of estrogen on breast cancer are mild, or not completely known.

Estrogens are a group of hormones that help regulate your menstrual cycle and support pregnancy. These hormones also have a variety of effect on the body, including protecting women's bones from thinning and helping to keep cholesterol at healthy levels.

The ratio and types of estrogen hormones differ in the premenopausal and postmenopausal years.

Pre-Menopausal Estrogens

• Estrone (E1): Estrone is made in the ovaries. E1 production decreases during pregnancy. It also decreases with menopause, but the body still continues to make limited amounts of E1 even after menopause. It has weak effects on the body, including maintenance of bone health.
• Estradiol (E2): Like E1, estradiol is made in the ovaries. It is the most prevalent estrogen in the body during the reproductive years, is responsible for the development of female sexual characteristics, and prepares the body for pregnancy. During pregnancy, E2 declines.
• Estriol (E3): Estriol is present in small amounts in premenopausal women. It is the main estrogen produced during pregnancy and it is made by the placenta. E3 is one of the hormones measured in a quad screen, a blood test used during pregnancy to assess the risk of fetal deformities.
• Estetrol (E4): This hormone is produced by a growing fetus and it is only produced during pregnancy. It may inhibit fertility, preventing you from becoming pregnant when you are already pregnant.

Menopausal Estrogens

As you approach menopause, the ovaries begin to become physically smaller and begin to slow down their production of hormones, including estrogen and progesterone. After menopause, estrone is the only estrogen hormone that the body continues to produce.

It is made in the ovaries and some steroid hormones are converted to estrone as well. After menopause, androgens (male hormones) produced by the adrenal glands are converted into E1 with the help of an enzyme called aromatase. Additionally, E1 is stored in body fat and muscle cells.

Low levels of E1 contribute to hot flashes, irregular periods, night sweats, mood swings, and other menopausal symptoms. Low estrogen levels also contribute to perimenopausal and menopausal vaginal dryness, which is often treated with estrogen creams.

There are three main kinds of estrogen produced outside of your body as well. Some are created by plants, some are made synthetically for treatment of medical conditions, and others are present in non-medical products.

Phytoestrogens—Plant-Based Estrogens

Phytoestrogens are found in plants and botanicals such as soybeans, red clover, legumes, cereal brans, and flaxseeds. They can have estrogen-like effects in your body.

While their actions are generally weaker than estrogens produced by your ovaries, they can have clinically apparent effects. Phytoestrogens may have either estrogen-like or anti-estrogen effects.

Dietary supplements that contain phytoestrogens are used to treat menopausal symptoms and can be obtained without a prescription. It is important to be careful and to discuss these supplements with your doctor if you are considering their use, even though they don't require a prescription.

Some of these herbal treatments should not be used by women who have breast cancer or who are at increased risk of developing the disease. Natural estrogens may protect against breast cancer, but they can also worsen it.

Synthetic Estrogens

Synthetic estrogens are produced for medical use and include estrogens like ethinyl estradiol. These compounds can be more powerful than natural estrogens and are important components of oral contraceptives (birth control pills) and hormone replacement therapy.

Additionally, some drugs have a substantial effect on estrogen, even if they are not estrogen substitutes. In particular, breast cancer drugs may be used to interfere with estrogen production of block its action. Estrogen receptor positive breast cancer is worsened by estrogen and may be treated with these medications.

• Tamoxifen: This drug is used to prevent the recurrence of breast cancer for premenopausal women who have estrogen receptor-positive breast cancer. Tamoxifen binds to estrogen receptors in the breast, blocking estrogen from causing the tumor to worsen. In the bones, however, tamoxifen can strengthen bones similar to the way in which natural estrogen does.
• Aromatase inhibitors, Aromasin, Arimidex, and Femara: These are drugs used by postmenopausal women who have estrogen receptor-positive breast cancer. They interfere with aromatase so that estrogen can no longer be produced.

Xenoestrogens 

Xenoestrogens, which are break down products of compounds in our environment, can be more potent than the estrogens your body makes. While there are still a lot of unknowns about these chemicals, too much exposure may have adverse effects on your health.

Xenoestrogens are among the endocrine disrupting agents, which are chemicals that adversely affect the human body's growth and development, potentially interfering with sexual development and reproduction, and increasing the risk of breast cancer.

Xenoestrogens can be found in some plastics, electronics, medicines, foods, soaps, and pesticides. Experts agree that the environment (water, air, soil, and plants) is being polluted by xenoestrogens from manufacturing runoff and the disposal of products.

Estradiol, and possibly estrone, increase the risk of developing breast cancer. And a lower level of these estrogens throughout a woman's lifetime is associated with a lower risk of developing breast cancer.

Factors such as pregnancy and breastfeeding alter estrogen levels in ways that are believed to play a protective effect. Having a first child before the age of 30, having more children, and breastfeeding are all associated with a lower risk of breast cancer due to the reduced production of estrogens during pregnancy and lactation (milk production).

Because oral contraceptives and hormone replacement therapies contain estrogen, they may increase the risk of breast cancer for some women.

A Word From Verywell

If you have an increased risk of breast cancer, your doctor will be careful about prescribing oral contraceptives or hormone replacement therapy. Be sure to discuss your concerns with your medical team and to have a good understanding of the pros and cons of these medications.

If you are considering taking an herbal preparation taking phytoestrogens, talk to a healthcare professional who has studied these supplements. Many physicians understand how to combine these alternative approaches with conventional medicine and can help you understand the potential risks and benefits.

And if you can avoid exposure to xenoestrogens, it is a good idea to do so. Many of these chemicals are not labeled and are difficult to avoid, but practicing reasonable caution until we know more about them is probably wise. For example, if you work with chemicals, be sure to protect yourself.