Editing Estrogen (section)

==Types and examples==
{{Chemical structures of major endogenous estrogens|align=right|caption=Note the [[hydroxyl group|hydroxyl]] (–OH) [[functional group|group]]s: estrone (E1) has one, estradiol (E2) has two, estriol (E3) has three, and estetrol (E4) has four.}}
The four major naturally occurring estrogens in women are [[estrone]] (E1), [[estradiol]] (E2), [[estriol]] (E3), and [[estetrol]] (E4). Estradiol (E2) is the predominant estrogen during reproductive years both in terms of absolute serum levels as well as in terms of estrogenic activity. During [[menopause]], estrone is the predominant circulating estrogen and during pregnancy estriol is the predominant circulating estrogen in terms of serum levels. Given by [[subcutaneous injection]] in mice, estradiol is about 10-fold more potent than estrone and about 100-fold more potent than estriol.<ref name="Labhart2012">{{cite book|author=A. Labhart|title=Clinical Endocrinology: Theory and Practice|url=https://books.google.com/books?id=DAgJCAAAQBAJ&pg=PA548|date=6 December 2012|publisher=Springer Science & Business Media|isbn=978-3-642-96158-8|pages=548–}}</ref> Thus, estradiol is the most important estrogen in non-pregnant females who are between the [[menarche]] and menopause stages of life. However, during [[pregnancy]] this role shifts to estriol, and in postmenopausal women estrone becomes the primary form of estrogen in the body. Another type of estrogen called [[estetrol]] (E4) is produced only during pregnancy. All of the different forms of estrogen are synthesized from [[androgen]]s, specifically [[testosterone]] and [[androstenedione]], by the [[enzyme]] [[aromatase]].{{cn|date=January 2025}}

Minor endogenous estrogens, the biosyntheses of which do not involve [[aromatase]], include [[27-hydroxycholesterol]], [[dehydroepiandrosterone]] (DHEA), [[7-oxo-DHEA]], [[7α-hydroxy-DHEA]], [[16α-hydroxy-DHEA]], [[7β-hydroxyepiandrosterone]], [[androstenedione]] (A4), [[androstenediol]] (A5), [[3α-androstanediol]], and [[3β-androstanediol]].<ref name="pmid23313336">{{cite journal | vauthors = Baker ME | title = What are the physiological estrogens? | journal = Steroids | volume = 78 | issue = 3 | pages = 337–340 | date = March 2013 | pmid = 23313336 | doi = 10.1016/j.steroids.2012.12.011 | s2cid = 11803629 }}</ref><ref name="pmid23123738">{{cite journal | vauthors = Miller KK, Al-Rayyan N, Ivanova MM, Mattingly KA, Ripp SL, Klinge CM, Prough RA | title = DHEA metabolites activate estrogen receptors alpha and beta | journal = Steroids | volume = 78 | issue = 1 | pages = 15–25 | date = January 2013 | pmid = 23123738 | pmc = 3529809 | doi = 10.1016/j.steroids.2012.10.002 }}</ref> Some estrogen metabolites, such as the [[catechol estrogen]]s [[2-hydroxyestradiol]], [[2-hydroxyestrone]], [[4-hydroxyestradiol]], and [[4-hydroxyestrone]], as well as [[16α-hydroxyestrone]], are also estrogens with varying degrees of activity.<ref name="pmid10865186">{{cite journal | vauthors = Bhavnani BR, Nisker JA, Martin J, Aletebi F, Watson L, Milne JK | title = Comparison of pharmacokinetics of a conjugated equine estrogen preparation (premarin) and a synthetic mixture of estrogens (C.E.S.) in postmenopausal women | journal = Journal of the Society for Gynecologic Investigation | volume = 7 | issue = 3 | pages = 175–183 | year = 2000 | pmid = 10865186 | doi = 10.1016/s1071-5576(00)00049-6 }}</ref> The biological importance of these minor estrogens is not entirely clear.