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QUESTION: I am blood type A, 53 years old, and on HRT because I am at risk for osteoporosis (S.D. of -1.0). My mother survived breast cancer when she was 72 yr. I think I would feel safer on estriol and progesterone but does it conserve bone? Thank-you for your dedication and fascinating work.
ANSWER: Estriol (E3) is one of the three major naturally occurring estrogens, the others being estradiol and estrone. Estriol is produced almost exclusively during pregnancy and is the major estrogen produced in the normal human fetus. During pregnancy the production of estriol depends on an intact maternal-placental-fetal unit. Fetal-placental production of estriol leads to a progressive rise in maternal circulating levels reaching a late-gestational peak several orders of magnitude greater than non-pregnant levels. Estriol has been suggested to be less carcinogenic than estradiol and estrone in animal studies. It has been shown that at doses effective for the relief of postmenopausal symptoms, estriol does not induce endometrial proliferation to the extent of the other estrogens. Topical estriol has also been used for the relief of postmenopausal genital atrophic changes and urinary incontinence.
Studies show that estriol can be effective with regard to both maintaining bone density and protecting the endothelial lining of the arteries from pathologic changes. In one study E3 significantly improved bone mineral density in elderly subjects. Other results are somewhat contradictory, but several Japanese studies showed good results with E3 and calcium supplementation.