Dr. Greer on Natural Hormones

What's all the Buzz About Estriol?

Michael Greer, M.D.

In 1978, Dr. Alvin Follingstad published “Estriol: The Forgotten Estrogen” in the Journal of the American Medical Association. He suggested that estriol (one of three estrogens naturally produced by a woman’s body) would be excellent for patients with breast cancer.

Estriol has been shown to demonstrate significant anti-cancer activity. In clinical studies, it prevented experimentally-induced breast cancer in rats.

High levels of estriol have been associated with a low incidence of breast cancer. In studies comparing patients taking estriol (E3) to those taking the estrogens estradiol (E2) and estrone (E1), the estriol patients had the lowest incidence of breast cancer.

Estriol protection is probably due to its effect and action at the receptor sites of the breast. Estriol can bind to the estrogen receptors in the breast, thus competing with stronger estrogens (estradiol and estrone) that encourage tumor growth. Phytoestrogens (found in foods such as soy) are weak estrogen-like compounds that work in much the same way.

It is helpful to understand how your body produces and processes its own estrogens. Your ovaries secrete mainly estradiol, while estrone is produced in your fat cells. These two estrogens are converted to estriol in the liver and in peripheral tissue.

Biest is a combination of 80% estriol and 20% estradiol. Special compounding pharmacies are able to formulate a custom medication for each patient’s needs as a gel, cream, tablets, or suppositories.

The risk of developing breast cancer also increases with age, rising from one in 217 at age 39, to one in 26 for women ages 40-59, to one in 15 for women 60-79. Breast cancer risk also increases with the duration and strength of estrogen use. Therefore it is advisable to increase estriol and decrease or entirely eliminate estradiol beyond the age of 60 to reduce the risk of breast cancer.

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