estrogens

Estrogens are a group of steroid hormones that regulate development and function of the female reproductive system and secondary sexual characteristics, while also influencing other tissues. In humans, the principal natural estrogens are estradiol (17β-estradiol), estrone, and estriol. Estradiol is the major circulating form in premenopausal women; estrone predominates after menopause; estriol is more abundant during pregnancy.

Biosynthesis occurs mainly in the ovaries, with contributions from the placenta during pregnancy and adipose tissue. The enzyme aromatase converts androgens such as testosterone and androstenedione into estrogens. Estrogens act through estrogen receptors, ERα and ERβ, which function as transcription factors in the nucleus (genomic actions) and via rapid signaling at the cell membrane (non-genomic actions).

Estrogens coordinate the menstrual cycle, promote growth and maintenance of reproductive tissues, and support bone density, lipid metabolism, and brain function. In males, estrogens are produced in smaller amounts and contribute to bone health and fertility.

Clinically, estrogens are used in contraception (combined oral contraceptives), hormone replacement therapy for menopause, and treatment of hypogonadism. In breast cancer and other estrogen-sensitive diseases, strategies to reduce estrogen activity include aromatase inhibitors and selective estrogen receptor modulators (SERMs) such as tamoxifen. Unopposed estrogen exposure raises risks of endometrial hyperplasia and certain cancers and increases thromboembolic risk.

Environmental estrogens (xenoestrogens) and phytoestrogens from plants can interact with estrogen receptors with weaker effects, influencing health in some contexts. Estrogen levels are commonly assessed by measuring estradiol in clinical settings.