Estrone

Estrone (E1) is one of the three main estrogens that the human body makes. The other two are estradiol (E2) and estriol (E3). Estrone is generally regarded as a weaker estrogen than estradiol.

Studies report very different values for the relative binding affinity of estrone. This measure describes how tightly a hormone binds the estrogen receptor. The values change with the lab method and the study design. No single set percentage captures that spread.

In lab tests, estrogens competed for cloned human estrogen receptors (ERα and ERβ). Estrone bound less tightly than estradiol at both receptors. It bound more tightly than estriol.¹

After menopause, estrone is the main estrogen in the blood. Fat and muscle make it from another hormone, androstenedione. This process is peripheral aromatization. The ovarian follicles do not make it.

Before menopause, the ovaries and other tissues make smaller amounts of estrone, along with estradiol.

Some women of childbearing age have high estrone levels. High estrone occurs most often with obesity or polyendocrine metabolic ovarian syndrome (PMOS / PCOS). It raises the ratio of estrone to estradiol. This shift may change how estrogen receptors signal and how the uterine lining responds.

RRM clinicians check estradiol as the main estrogen in hormone testing. They may add estrone as part of a broader hormone workup when metabolic problems are more complex.