What is Estrogen?

Estrogens are hormones that are important for sexual and reproductive development, mainly in women. They are also referred to as female sex hormones.

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Estrogen's function

In women, estrogen is produced mainly in the ovaries, but it is also produced by fat cells and the adrenal gland. Estrogen is involved in the onset of puberty, playing a role in development of so-called secondary sex characteristics, such as breasts, and pubic and armpit hair. It also helps regulate the menstrual cycle.

During pregnancy, the placenta produces estrogen. 

Estrogen also plays a role in bone formation, blood clotting and other body functions. The hormone also affects the brain, and studies also show that chronically low estrogen levels are linked with reduced mood.

Men produce estrogen as well, but at lower levels than women. In men, estrogen is thought to affect sperm count.

Changes in estrogen levels

Estrogen levels naturally increase during puberty, and also in pregnancy.

Estrogen levels fall after menopause, or when a woman stops menstruating. This reduction in estrogen production can cause symptoms such as hot flashes, vaginal dryness and loss of sex drive.

Other conditions that can cause estrogen levels to drop include hypogonasim — or diminished function of the ovaries — and polycystic ovarian syndrome. Extreme exercise and anorexia can also cause a decrease in estrogen levels because women with low body fat may not be able to produce adequate amounts of estrogen.

Estrogen levels also decrease after childbirth.


Medications with estrogen

Estrogen in found in most oral birth control pills (along with the hormone progestin.)

Hormone replacement therapy — a treatment to reduce symptoms of menopause — also includes estrogen (which can be given in combination with progestin). Because hormone replacement therapy comes with risks, including an increased risk of breast cancer, it should be given on a case-by-case basis. Women who do start hormone replacement therapy are encouraged to try the smallest dose for the shortest amount of time, according to the Food and Drug Administration.

Estrogen's role in cancer

The majority of breast cancers are sensitive to estrogen, meaning that estrogen promotes tumor growth. These cancers are called hormone receptor positive breast cancers. For people with these cancers, treatments to lower estrogen levels or block estrogen production can be used to help prevent cancer recurrence after surgery, or to slow cancer growth.

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