estradiol

Estradiol is the strongest of the natural estrogens and the workhorse of the female reproductive years. If estrogen is a family, estradiol is its most powerful member — the form clinicians measure when they want to know how active a woman's ovaries are. Its abbreviation, E2, reflects the two hydroxyl groups on its steroid skeleton.

Estradiol is produced mainly by the granulosa cells of the growing ovarian follicle. This relies on teamwork between two follicle cell types: theca cells, under the influence of LH, make androgen precursors, and granulosa cells, under FSH, use aromatase to convert those androgens into estradiol — the classic two-cell, two-gonadotropin model. Estradiol blood levels therefore rise and fall in step with follicle growth across the menstrual cycle, peaking just before ovulation.

Functionally, estradiol thickens the uterine lining (the proliferative endometrium), produces fertile cervical mucus, supports bone and cardiovascular health, and provides the feedback signals that govern the pituitary. Because it is rapidly broken down by the liver when taken by mouth, pharmaceutical estradiol is often given through the skin (patches or gels) or as longer-acting esters; this is a practical caveat for hormone therapy, not a flaw in the natural hormone.