Estrogen Dominance and Thyroid Issues

Tess Thompson



Estrogen is the term used for female sex hormones secreted by the ovaries. Before understanding estrogen dominance, it is important to know what changes take place in a women’s body during a menstrual cycle.

The menstrual cycle is controlled by hormones. The estrogen level increases to stimulate the ovarian follicles. Under the influence of several hormones, only one follicle, known as the tertiary or Graafian follicle, continues to grow and forms the ovum or egg. As the follicle matures, it releases increased amounts of the most powerful female estrogen, known as estradiol. The matured follicle ruptures, following the release of an egg— leading to the formation of yellow endocrine tissue known as corpus luteum. This endocrinal tissue produces natural progesterone for:

  • Preparing the uterus to receive the fertilized egg
  • Maintaining the uterus for pregnancy
  • Counterbalancing the side effects of too much of estrogen

This is the second half of the menstrual cycle after ovulation, and if the egg is not fertilized, then the menstrual flow begins. Estrogen dominance in a women’s body may occur due to any of the following reasons:

  • Absence of ovulation due to immaturity, post-maturity, pregnancy, oral contraceptive pills or dysfunction of the ovary
  • Menopause
  • Improper diet
  • Counterfeit estrogens prescribed during and after menopause

High estrogen levels lead to excessive production of thyroid-binding globulin (TBG) by the liver. If the TBG levels are high it will bind more thyroid hormones, thus reducing the free thyroid hormones available in the blood. Therefore, thyroid hormones cannot be used by the cells that require them for maintaining the body’s metabolism.

Although there are enough thyroid hormones in the blood, they are not taken up by the body’s cells as they are inactivated by TBG. Estrogen dominance therefore often leads to thyroid problems in women. This is one of the reasons why blood tests reveal ‘normal’ levels of thyroid hormones in such situations, but some women still show classical symptoms of thyroid problems.

Medical practice has over the years started to rely more on laboratory and imaging tests. Relying only of modern diagnostic procedures can sometimes delay diagnosis. The diagnosis also must be read along with visible physical symptoms observed by a physician or as reported by the patient. The effect of estrogen dominance on thyroid conditions is a typical example supporting the importance of physical symptoms.

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