Estrogen is one of two major female steroidal sex hormones, the other being progesterone. The main source of estrogen in females prior to menopause is the ovaries, after which the main source becomes the adrenal glands and fat tissue. Oestrogen is also produced by the placenta during pregnancy. Estrogen levels fluctuate throughout life, naturally increasing during puberty and pregnancy, and falling after menopause. During the menstrual cycle, estrogen levels peak during ovulation dropping off if pregnancy doesn’t occur.
The main roles of estrogen in the body are to increase the growth and production of cells, the development and regulation of the female reproductive system, and secondary sex characteristics - breasts, pubic hair etc. Oestrogen is also involved in maintaining bone density, plays a role in blood clotting, and affects skin, hair, mucous membranes, and the pelvic muscles.
The body produces 3 different types of estrogen:
E1 - Etrone: medium strength, predominant after menopause (adrenal glands)
E2 - Estradiol: strongest form, predominant during childbearing age (ovaries & adrenal glands)
E3 - Estriol: weakest form, predominant during pregnancy (placenta & liver)