Estradiol is a 17β-hydroxylated steroid, the most potent of the three estrogens.
Mechanism: Binds estrogen receptors α and β. In women, drives menstrual cycle architecture, bone density, vascular health, and cognition. In men, produced via aromatization of testosterone. Essential for libido, bone health, lipid profile, and joint comfort.
Lab range: Women: varies by cycle phase (50–400 pg/mL). Men: 20–55 pg/mL is typical optimal.
Caveats: Too high or too low both produce symptoms. The 'lower is better' myth in men's hormone optimization is wrong. Crashed estradiol from over-aromatase-inhibition causes joint pain, low libido, and vascular problems.