østrogens

Östrogens are a group of steroid hormones essential for the development and regulation of the female reproductive system and the maintenance of secondary sexual characteristics. The principal estrogens in humans are estradiol (E2), estrone (E1), and estriol (E3). In premenopausal women, the ovaries and placenta are the main sources; after menopause, peripheral tissues such as adipose tissue contribute via aromatization. In men, estrogens are present at lower levels and contribute to reproductive and bone health.

Estrogen action is mediated primarily by estrogen receptors, especially ER alpha and ER beta. When bound by estrogens, these receptors can act as transcription factors to regulate gene expression (genomic effects). They can also trigger rapid, non-genomic signaling through membrane-associated receptors, with effects that depend on tissue type, receptor distribution, and local hormone levels.

Estrogens are synthesized from androgens by the enzyme aromatase (CYP19A1). Production varies with age, menstrual cycle, pregnancy, and body fat. After production, estrogens are metabolized in the liver and excreted in urine and bile. Tissue distribution and circulating levels determine diverse functions in different organs.

Biological roles include development of the female reproductive tract and breasts, regulation of the menstrual cycle and ovulation, and the maintenance of bone density and metabolic health. In men, estrogens support spermatogenesis and bone integrity.

Clinically, estrogens are used in hormone replacement therapy, combined birth control formulations, and gender-affirming hormone therapy. Deficiency can cause hot flashes and osteoporosis; excess estrogen or estrogen therapy carries risks such as thromboembolism and certain cancers, influenced by dose, route, and duration. Environmental compounds with estrogen-like activity (xenoestrogens) can also affect physiological processes.