Estrogen Dominance In PCOS

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What Does Estrogen Do?

Estrogen is a major hormone produced by the ovaries and in small quantities by the adrenal glands, and responsible for the development of female sex characteristics. Estrogen is required for proper development of sexual organs, completion of skeletal system, regulation of the menstrual cycle and maintenance of pregnancy.

During the menstrual cycle, estrogen is secreted by the developing egg follicle and aids in thickening of the endometrium for ovulation and possible pregnancy.

Also one of the major hormones of pregnancy, estrogen supports the production of fluid in the reproductive tract which enhance the survival of sperm by slightly neutralizing cervical secretions. Towards the end of pregnancy, estrogen promotes the growth of milk ducts within the breasts and enhances the effect of prolactin (major hormone responsible for lactation in the female).

Synthetic Estrogen

Estrogen is also the main hormone found in birth control pills. Each pill is different, containing varying amounts of estrogen and/or progesterone.

As a woman ages and she enters Menopause, her estrogen levels begin to decline. For that reason, some physicians may prescribe estrogen replacement therapy, to minimize some of the symptoms experienced.

Estrogen Dominance in Women with PCOS

PCOS is the most common cause of ovulatory infertility and it’s believed that estrogen dominance, is part of the reason.

Lack of ovulation results in continuous high levels of estrogen and insufficient progesterone. Unopposed by progesterone, constant estrogen exposure may cause the endometrium to become excessively thickened, which can lead to heavy and/or irregular bleeding (dysfunctional or anovulatory uterine bleeding).

Over many years, endometrial cancer may result due to continuous stimulation by high levels of estrogen unopposed by progesterone, causing the uterine lining to thicken and fail to properly shed.

Heavy Menstrual Bleeding and PCOS

For women with menorrhagia (excessively prolonged or heavy menstruation), the administration of an estrogen may be recommended to temporarily stop the bleeding and stabilize the endometrial lining. Alternatively, progestins may be administered orally to try to achieve a controlled bleeding episode. Low-dose oral contraceptive pills or intrauterine devices (IUD) such as Mirena (a levonorgestrel-releasing intrauterine system) are also options to reduce heavy bleeding. In some cases, an endometrial ablation, a surgical procedure that removes most of the endometrial lining, is recommended.

Environmental Causes of Estrogen Dominance

While high estrogen levels along with a lack of progesterone is a major factor of the estrogen dominance seen in women with PCOS, environmental factors can also play a role.

Chemicals in our environment, known as xenoestrogens, can mimic naturally occurring estrogen in our bodies and act as endocrine disruptors.

Some sources of endocrine disruptors include pesticides, Bisphenol A (BPA) and phthalates (found in plastic containers, water bottles, and paper receipts), and parabens (often found in skin and hair care products). It is thought that BPA disrupts signaling pathways, perhaps by interfering with estrogen receptors. BPA levels have been shown in studies to be higher in women with PCOS.

To minimize your exposure of environmental disruptors, follow these tips:

  • Choose glass containers to heat and store food
  • Drink beverages from glass bottles or those marked “BPA-free”
  • Buy canned goods marked “BPA-free”
  • Eat organic and “hormone-free” foods
  • Wash hands well after handling paper receipts
  • Check ingredients in skin and hair care products, buying “paraben-free” instead
  • In addition, eating a diet rich in antioxidants can also help to protect your estrogen receptors from environmental damage.

Edited by Angela Grassi, MS, RDN


Abnormal Uterine Bleeding: A Guide for Patients. American Society of Reproductive Medicine Fact Sheet accessed June 8, 2015

Barrett ES1, Sobolewski M2. Polycystic ovary syndrome: do endocrine-disrupting chemicals play a role? Semin Reprod Med. 2014 May;32(3):166-76.

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