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ESTROGEN
TYPES OF ESTROGEN
HUMAN ESTROGEN
There are three estrogens produced by the body. Estradiol is the primary hormone produced before menopause; estrone is the primary hormone produced after menopause, and estriol (the primary hormone during pregnancy) is converted from estradiol and estrone.
CONJUGATED EQUINE ESTROGENS
Premarin, whose generic name is conjugated estrogen, is the most prescribed estrogen primarily because it has been the most studied. Because it originates from horse urine, the manufacturer claims on every bottle: "obtained exclusively from natural sources".
Although Premarin contains estrone, almost half of the estrogen is in the form of equine (horse) estrogen, which is not found in the human body. Premarin seems to produce higher estrogen levels and has more of an effect on the liver than the non-equine estrogens. For this reason, for long-term therapy there is more interest in prescribing the 0.3 mg (green tablet) as the standard dose instead of the 0.625 mg (maroon tablet).
Some primary care providers feel that the equine estrogens in Premarin may be responsible for the breast tenderness and other side effects some women experience. Others attribute these effects to Premarin’s higher estrogenic blood levels.
A recently published study suggested that one of the minor ingredients in Premarin may be capable of inducing DNA damage in hormone sensitive cells.
Premarin has been combined with medroxyprogesterone in two products Prempro and Premphase.
LABORATORY ESTROGEN SYNTHESIZED FROM PLANT SOURCES
Estradiol and Estrone are two estrogens produced from substances found in plants. They are chemically identical to those produced by the body and have been shown to have all the benefits of estrogen mentioned previously.
Estradiol is also called 17beta-estradiol or E2 and is considered the most potent of the estrogens. Some evidence indicates that it may be more effective than other estrogens on the cardiovascular system, although the degree of benefit of estrogens for this purpose is a subject of debate.
Estradiol is found in Estrace tablets and cream. It is also the active ingredient in all of the commercial transdermal patches--Alora, Climara, CombiPatch, Estraderm, Fempatch, and Vivelle. The new combo products FemHRT and Ortho-Prefest also contain estradiol as their estrogen. The compounded product Bi-Est contains 20% estradiol and Tri-Est contains 10% estradiol.
Estrone or E1 is the primary estrogen in estropipate (Ogen, Ortho-Est). It is also found in the estrogens Menest and Estratab, although both of these have between 6-15 % equine estrogens. Cenestin is a mixture of both estrone and estradiol, although it too has a small amount of equine estrogens. The compounded product Tri-Est contains 10% estrone.
Estriol or E3 is the weakest estrogen. There are several provocative studies that suggest women with higher natural levels of estriol have a lower incidence of breast cancer. It is thought that estriol may act as an antiestrogen in the breast tissue. However, much more research is needed in this area before any conclusions can be made.
Heart: It is uncertain whether estriol by itself will provide cardiovascular protection. Although it appears to have an effect on blood vessels, it does not seem to have a beneficial effect on cholesterol levels.
Bone: There are contradictory reports about the effects of estriol on osteoporosis prevention. Early studies indicated that high levels (8-12 mg/day) were necessary to exhibit bone density benefits. Several recent studies have shown beneficial effects (comparable to Premarin 0.625 mg) on doses as low as 2 mg /day.
Uterus: It had been thought (and often reported in many books on natural hormones) that oral estriol did not require the addition of a progesterone compound to prevent uterine cancer. This may be true for short-term treatment (6-12 months). However, a recent study has shown that oral estriol taken alone for a 5-year period caused a threefold increase in uterine cancer--which would indicate a need for the addition of progesterone.
Hot Flashes: Estriol has been shown to be effective in treating menopausal symptoms. Although oral doses of 2 mg/day have been shown to be effective in the improvement of symptoms such as hot flashes and insomnia, some women may require doses as high as 8 mg/day. At this higher dosage, nausea may be a limiting factor.
Urinary/Vaginal: Estriol, in the form of a vaginal cream or suppository has clearly been shown to be effective in the treatment of postmenopausal vaginal dryness, chronic vaginitis, and recurrent urinary tract infections.
Availability: Estriol is not commercially available in the U.S. at this time. Compounding pharmacies are able to formulate it in a variety of forms. Estriol is often added to the other human estrogens in an 80% concentration in either a Bi-Est or Tri-Est formulation. These products try to mimic the ratio of hormones that are naturally found in the body and try to take advantage of the relative safety of estriol along with a low dose of the potent estrogens. Bi-Est and Tri-Est are not commercially available, and there are no studies regarding their effectiveness. It is generally thought that the 2.5 mg dose is equivalent to 0.625 mg conjugated estrogens.
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