Bioidentical Hormones for Menopausal Therapy

Cynthia K Sites


Women's Health. 2008;4(2):163-171. 

In This Article

Foundation & Claims of "Bioidentical" Hormones

Bioidentical hormones are typically derived from plant extracts and chemically altered to be identical in structure to endogenous human hormones.[5] Sources for these hormones often include plants (soy or yams), although de novo synthesis of hormones in the laboratory is also possible. Bioidentical is not a medical definition but one that has become popular with the media and public.[52,55] Celebrity self-help books written by Suzanne Somers and Michael Platt, along with many internet websites, promote bioidentical hormones as safer alternatives to conventional hormones prescribed for women to get "the exact dose that they require" to replace the body"s estrogen and progesterone.[8,9] These books state that FDA-approved products are "drug hormones," which only treat symptoms, and that nothing is being replaced. Bioidentical hormones are further described as the "secret elixir" and "fountain of youth", which can reverse the aging process and keep people mentally sharp and fit, although none of these claims have been clinically tested. As a result of these unsupported claims, the FDA recently sent warning letters to seven compounding pharmacies that were making false claims regarding their products for menopausal women.[55]

A characteristic of bioidentical estrogen compounds is the frequent inclusion of estriol in the product. The metabolism of estradiol includes its reversible metabolism to estrone, with further irreversible conversion to estriol.[10] After menopause, estradiol is no longer produced by the ovaries, but estrone is produced in fat through the conversion of androstendione. Estriol is the end product of estrone and estradiol metabolism.[10] The reason for the inclusion of estriol, a weak estrogen, which is an end product of metabolism in bioidentical estrogen formulations, is largely based on animal data suggesting that estriol may be safer with regard to the development of breast cancer. In studies by Lemon, virgin Sprague-Dawley rats premedicated with estriol were exposed to a known carcinogen.[11,12,13,14] In the animals pretreated with estriol, rats had reduced tumor induction. Furthermore, when estriol was implanted after exposure to the carcinogen, tumors tended to regress. However, other experiments suggested that ethinyl estradiol had the same effects in these rats. Unfortunately, when older women with breast cancer were treated with estriol, 25% had increased growth of metastases.[15] Overall, his experiments led him to conclude that continuous estriol was not an effective therapy for breast cancer in women. Thus, the "safer" theory of estriol therapy over estradiol and estrone with regard to breast cancer prevention in postmenopausal women has not been established.


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