Estrogen Dominance and Cancer Risk

Estrogen is a double-edged sword when it comes to cancer. It can either promote tumour growth or protect against it. To understand how estrogen can play these two opposing roles, we must first understand that there are many forms of estrogen that are produced in the body, or that enter the body from the environment.

The estrogens produced in the body have different levels of potency. Estradiol is the most potent, some 80 times more potent than the weakest endogeneous estrogen, estriol. Estrone is the medium-grade estrogen, roughly 12 times more potent than estriol. These three estrogens do roughly the same work, encouraging growth of healthy hearts, bones, skin and uteri at varying levels at various stages of life.

The pre-pubescent girl produces only small amounts of estrogen. When her ovaries activate in her teen years, the amount of estradiol skyrockets to 20 times that of a child and thus begins her lifelong exposure to varying levels of estrogen that could harm or heal her. Women who start menstruating earlier, or stop later, have a longer exposure to stronger forms of estrogen. This increases their likelihood of development estrogen-sensitive cancers like breast cancer or uterine cancer. During her fertile years, overexposure to estrogen through birth control pills, xenoestrogens and her own body’s over-production can promote the development of breast cancer. Removal of excess estradiol via a high fibre diet that includes cruciferous vegetables, natural soy foods and flaxseed can protect a woman from cancer. Indeed, plant estrogens found in soy and flax are an example of good estrogens during this stage in life.

As menopause approaches, estradiol production by the ovaries drops off but fat cells and the adrenal glands continue to produce the less potent estrone for many more years to come. Estrone is so-called “bad” estrogen because it is associated with obesity, being produced by fat cells that have been overfed. Into menopause, in the old day,  many women may have chosen estrogen replacement therapy in an attempt to maintain their youth and vigor. However, after a generation of follow-ups, doctors now know that hormone replacement was hardly a cure-all for the aging woman: Estrogen replacement therapy resulted in a 30 percent increase in breast cancer and a 10-fold increase in uterine cancer. The large majority of breast cancer are estrogen-receptor-positive which means that cutting off estrogen supply will stop tumour growth. Hence, it is particularly important for older woman to avoid being overweight and estrogen dominant at this stage in life.


Estrogen: The Natural Way by Nina Shandler. Villard, New York, 1997. Introduction, pages xviii-xix.

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