There are four different types of estrogen: estrone, estradiol, estriol, and estetrol. Together, these hormones are responsible for the maturation and growth of a woman’s reproductive system and the development of secondary sex characteristics. Here is a quick overview of each type:
Estrone (E1) is a weak estrogen that plays an important role in the release of estradiol. Most estrone is made in the ovaries from cholesterol. However, some estrone is made in the adrenal glands and secreted into the bloodstream or produced in fatty tissues. Estrone is formulated commercially for the treatment of menopausal symptoms.
Estradiol (E2) is a major sex hormone. Of the four types of estrogen, it plays the biggest role in the development of a woman’s reproductive organs. It is also involved in:
- Breast development.
- The widening of the hips.
- The distribution of fat.
- Maintaining a viable pregnancy.
- Promoting bone strength.
- Breast growth and milk production.
Estradiol is available commercially in many formulations for the treatment of endometriosis and polycystic ovarian disease and for use as a contraceptive. When a female reaches menopause, the levels of estradiol drop gradually.
Estriol (E3) is another weak estrogen and a minor sex hormone. The levels of estriol are usually not detectable in non-pregnant females. However, during pregnancy, high concentrations of estriol are produced by the placenta. Estriol is often used to treat symptoms of menopause.
Estetrol (E4) is found only in pregnant females and is made by the fetal liver, where it plays an important role in the growth of the placenta. It is a relatively weaker type of estrogen. Commercial preparations are usually for the management of menopausal symptoms such as hot flashes, headaches, and vaginal dryness.