About Hormones Women What is Estrogen?
What is Estrogen?
Most women do not understand that 'estrogen' is not actually a hormone, like testosterone or progesterone, but is the word used for a class of molecules doing estrogen-like activities in the body. Many molecules are estrogens. A woman’s principal estrogens are estradiol, estrone, and estriol, described below. It is important to recognize this when you and your doctor are deciding what kind of hormone replacement therapy you’ll be using.
What are estrogens and how do they work?
The “job” of estrogens is to circulate throughout the body and attach themselves to cells that release estrogen receptors (ERs). Estrogens and those receptors function like a key and a lock. When you place a key in a lock the door opens; when estrogen attaches to an ER the body is opened for a series of events. These events mediate activity we see in tissue, such as building up of the lining of the uterus, or preventing bone density loss. Many different estrogens can lock on to an ER and each will have a different degree of effectiveness and diverse effects in the various tissues.
Let’s use estradiol for an example. It is the most potent of the estrogens produced by the ovary. A tiny amount circulating in your blood stream can affix to an ER and cause powerful changes in estrogen responsive tissues. In comparison, two other estrogens are estrone and estriol, created in stages as estradiol metabolizes. As by-products of the metabolic process, these two perform their functions but are both progressively weaker than estradiol.
How do I know if an estrogen is 'natural' or 'synthetic'?
That question is often asked by women looking for more ‘natural' approaches to HRT after hearing that the natural estrogens cause fewer side effects. Unfortunately, they perceive ‘natural’ as herbal or plant-based rather than as derived from chemicals. Because of that, women often choose to use things like yam extract or other herbs rumoured to act like estrogen in the body. Please understand that yams have no molecules with any significant estrogen activity. They do contain a precursor molecule, diosgenin, which can be chemically transformed into many different estrogens. At OptiGenics, we prefer to make a different but very important distinction about effectiveness, rather than to debate natural vs. synthetic estrogens. The difference we think is important is not about natural vs. synthetic, but between hormones that are "naturally" found in the human body. Hormones naturally occurring in the body are called bioidentical hormones. Hormones that might behave similarly in some tissues but are found elsewhere (plants, chemicals) and are not naturally found in the human body are called exogenous or foreign hormones.
Estradiol, estrone, and estriol, and all of their metabolites are bioidentical hormones "naturally" found in the human body. However, Premarin, the most commonly prescribed replacement estrogen formulation, mixes two bioidentical estrogens (estradiol and estrone) with 10 or more horse estrogens that are not found in the human body. The primary difficulty with exogenous (non-human) hormones is that even though we have strong research on their activity in some tissues, we don’t have conclusive studies of their effects on other tissues.
Premarin is a good example of why we prefer to use hormones found in humans rather than worry about if something is "natural" or "synthetic". Premarin is natural because it is derived from the urine of pregnant mares (female horses) and is not synthesized. But it is still not natural for human women. It contains many estrogens that do not naturally occur in a woman's body. Some of those hormones, like equilenin, are very potent estrogens. Equilenin is even more potent than estradiol. Do human women need that much potency? How is that level of hormone processed? The levels of all extra-potent hormones must be monitored closely. Sadly, blood and saliva tests are not readily available to monitor the levels of foreign hormones including the estrogen substitutes known as raloxifene (Evista) and tamoxifen (Novaldex). Why is this particularly important? In the next section you will learn how the methods and circumstances of taking an estrogen (and many other hormones) can dramatically alter a woman’s blood levels.
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