Estriol

Estriol (E3), also known as oestriol, is a steroid, a weak estrogen, and a minor female sex hormone[1]. It is one of three major endogenous estrogens, along with estradiol and estrone. Estriol is synthesized in very high quantities by the placenta during pregnancy, making it the most produced estrogen in the body at that time[1]. However, its circulating levels are similar to those of other estrogens due to a relatively high rate of metabolism and excretion[1].

Biological Activity

Estriol is an estrogen, specifically an agonist of the estrogen receptors ERα and ERβ[1]. It is a far less potent estrogen than estradiol, and as such is a relatively weak estrogen[1]. Estriol has mixed agonist–antagonist (partial agonist) activity at the ER; on its own, it is weakly estrogenic, but in the presence of estradiol, it is antiestrogenic[1]. At high concentrations, estriol also acts as an antagonist of the GPER, a membrane estrogen receptor[1].

Medicinal Use

Estriol is used as a medication, particularly in menopausal hormone therapy[2]. It is available as a prescription-only cream to treat symptoms of vaginal dryness caused by a drop in estrogen levels during the perimenopause and menopause[2]. The cream helps to restore elasticity and lubrication to the vagina and surrounding tissues, relieving soreness and irritation[2]. Estriol can also be used to treat recurrent urinary tract infections (UTIs)[2].

Administration and Dosage

Estriol cream comes in a pack with a clear plastic applicator, and each applicator dosage contains 0.5mg of estriol[2]. The recommended usage is one applicator per day for three or four weeks, and then twice per week[2]. It is best applied before going to bed, and the applicator needs to be thoroughly cleaned after each use[2].

Benefits and Side Effects

Estriol can relieve dryness and soreness, and it may also be used to treat recurrent UTIs[2]. Side effects may include vaginal discharge and some itching or irritation after applying the cream[2]. Estriol is considered safer than estradiol, as it is less likely to cause side effects like high blood pressure and blood clots[3].

Pregnancy and Hormone Therapy

During pregnancy, estriol levels rise to help keep the uterus healthy and prepare the body for childbirth and breastfeeding[3]. Estriol levels that are too high or low may indicate a problem with the baby or pregnancy[3]. Providers may also use estriol as a hormone therapy to ease menopause symptoms, as it is the weakest of the three estrogen types and may be safer[3].

Citations:

[1] https://en.wikipedia.org/wiki/Estriol

[2] https://www.balance-menopause.com/menopause-library/vaginal-oestrogens-what-is-estriol-and-how-do-i-use-it/

[3] https://my.clevelandclinic.org/health/articles/22399-estriol

[4] https://pubmed.ncbi.nlm.nih.gov/9577246/

[5] https://www.amazon.com/Micronized-Gluten-Free-Dairy-Free-Cruelty-Free-Phenoxyethanol-Free/dp/B0B9ZF144X