Estrogens (or oestrogens) are a group of steroid compounds that function as the primary female sex hormone. They are produced primarily by developing follicles in the ovaries, the corpus luteum and the placenta. Some estrogens are also produced in smaller amounts by other tissues such as liver, adrenal glands and the breasts. These secondary sources of estrogen are especially important in post-menopausal women.
The three naturally occurring estrogens are estradiol, estriol and estrone. In the body these are all produced from androgens through enzyme action. Estradiol is produced from testosterone and estrone from androstenedione. Estrone is weaker than estradiol, and in post-menopausal women more estrone is present than estradiol.
While estrogens are present in both men and women, they are found in women in significantly higher quantities. They promote the development of female secondary sexual characteristics, such as breasts, and are also involved in controlling the menstrual cycle, which is why most birth control pills contain estrogens.
The use of estrogen, especially together with progesterone, is a controversial treatment for the symptoms of menopause which may do as much harm as good.
A range of other synthetic and natural substances have been identified that possess estrogenic activity. These include bisphenol-A, phthalate esters and nonylphenol.
References
Fang H, Tong W, Shi LM, Blair R, Perkins R, Branham W, Hass BS, Xie Q, Dial SL, Moland CL, Sheehan DM. 2001. Structure-activity relationships for a large diverse set of natural, synthetic, and environmental estrogens. Chemical Research in Toxicology 14:280-294.
Further reading
Barbara Seaman, "The Greatest Experiment Ever Performed on Women: Exploding the Estrogen Myth", Hyperion Press, 2003, hardcover, ISBN 0786868538
For example, estrogen increases the concentration of an enzyme needed to synthesize acetylcholine, a brain chemical that's critical for memory.
Estrogen also enhances communication between neurons in the hippocampus, an area of the brain that is important for verbal memory.
She argues that many studies that have found no effect of estrogen have used tests of cognitive function that are too blunt to differentiate different aspects of cognitive function.
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