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.
Bio-identical estrogens have been shown to be clinically effective:
- for the treatment of menopausal symptoms.
- for the the treatment of postmenopausal problems including vaginal atrophy, dryness, or infections, painful intercourse, and various conditions of the urinary tract.
- in decreasing the risk of osteoporosis and colorectal cancer.
In contrast to bio-identical estrogens, NON-bio-identical conjugate equine estrogens (CEE) are commonly prescribed. These conjugated estrogens are derived from pregnant mares' urine; however, most estrogens found in horses are NOT naturally produced by humans. Published research has shown that the risk of breast cancer is increased with the long term use of CEE and the risk is further increased when the synthetic progestin medroxyprogesterone acetate (MPA) is added.