Estrogen Types and Their Connection to Breast Cancer

Naturally Occurring, Synthetic, Plant-Based, and Xenoestrogens

Estrogen, a hormone that controls many aspects of female physiology, can be associated with breast cancer. And women (and men) can be exposed to other types of estrogen as well, such as synthetic estrogens (used in medication), plant-based estrogens (sometimes found in supplements), and xenoestrogens (a byproduct of commercial chemical compounds). Each estrogen type may impact breast cancer differently. But often, the effects of estrogen on breast cancer are mild, or not completely known.

types of estrogen
Verywell / Brianna Gilmartin 

The Role of Estrogen

The female 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.

In addition to helping to regulate a woman's menstrual cycle and support pregnancy, these hormones have a variety of other effects 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

Before a woman reaches menopause, her body produces four different types of the hormone:

  • Estrone (E1): Estrone is made in the ovaries. E1 production decreases during pregnancy and with 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, though in limited amounts.

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.

Healthcare providers may treat the symptoms of low estrogen with oral (by mouth) hormone replacement therapy (HRT) for a short period of time, but prolonged use has been associated with an increased risk of breast cancer.

Estrogens Produced Outside the Body

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 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 discuss these supplements with your healthcare provider if you are considering their use.

Some 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.

Estrogen receptor-positive breast cancer is worsened by estrogen and may be treated with these medications:

  • Tamoxifen: This drug, sold under the brand names Nolvadex and Soltamox, 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. Tamoxifen can strengthen bones similar to the way in which natural estrogen does.
  • Aromatase inhibitors: Aromasin (exemestane), Arimidex (anastrozole), and Femara (letrozole) are drugs used by postmenopausal women who have estrogen receptor-positive breast cancer. They interfere with aromatase so that estrogen levels are lowered.


Xenoestrogens, which are breakdown 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.

Estrogen and Breast Cancer Risk

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 have 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, there is a small potential they may increase the risk of breast cancer for some women.

While we know that estrogen receptor-positive breast cancers are worsened by estrogen, other breast cancer types typically are also more common among women who have had a higher lifetime exposure to estrogen.

A Word From Verywell

If you have an increased risk of breast cancer, speak with your healthcare provider about the pros and cons of oral contraceptives and hormone replacement therapy before taking them. Likewise, mention any supplements you're considering. 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 more about them is known is probably wise. For example, if you work with chemicals, be sure to follow all recommended safety protocol.

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