Estrone is one of three principal estrogens (E1, E2, E3). After menopause, it becomes the dominant circulating estrogen as ovarian E2 production drops.
Mechanism — Produced primarily in adipose tissue via aromatization of androstenedione. Weaker estrogenic activity than E2 but still bioactive. Can be converted back to E2.
Lab range — Premenopausal women: 17-200 pg/mL. Postmenopausal: 7-40 pg/mL. Men: 10-60 pg/mL.
Caveats — Elevated E1 in men correlates with body fat — weight loss is the lever. In post-menopausal women, E1 dominance favors certain hormone-sensitive risks.