Estrogens actually refers to a group of related hormones, each with a unique profile of activity. Under normal circumstances, a woman’s circulating estrogen levels fluctuate based on her menstrual cycle. For Hormone Replacement Therapy, these hormones are often prescribed in combination to re-establish a normal physiologic balance. The three main estrogens produced in female humans are:
- Estrone -E1- (10-20% of circulating estrogens) is the primary estrogen produced after menopause
- Estradiol -E2- (10-30% of circulating estrogens) is the most potent and major secretory product of the ovary, and the predominant estrogen produced before menopause.
- Estriol -E3- (60-80% of circulating estrogens) causes little or no buildup of the endometrium, and is very effective in alleviating vaginal and urinary symptoms in postmenopausal women. Estriol has been shown to be clinically effective for the treatment of menopausal symptoms as well as postmenopausal problems including vaginal atrophy, dryness, vaginal infections, painful intercourse, and various conditions of the urinary tract. Estriol is produced in very large amounts during pregnancy. High levels of estriol are found in vegetarians and Asian women, who have a much lower incidence of breast cancer.