Natural Hormones vs. Synthetic Hormones

By Elizabeth Lee Vliet, MD
Excerpted and condensed from Women, Weight and Hormones, p. 214-216
Evans and Company, 2001

Many women express a desire to take only natural hormones. But the words “natural” and “synthetic” can be very confusing to patients and doctors alike.

Whether a compound is biologically “natural” (to plants, horses, or whatever), is not the issue. The molecule shape, make-up, and structure must be identical to what is made in the human body to provide the perfect “key” to unlock the body’s receptor sites.

A compound that meets these requirements is called “bioidentical.” The bioidentical hormone replacement process is sort of like getting a spare key from the locksmith. The manufacturer (the ovary) stops making your own hormone at menopause, so a “locksmith” (the laboratory) makes an exact duplicate hormone molecule for you to use if you choose to.

In today’s common usage, “synthetic” has come to mean “artificial,” but this is not always correct. Synthetic simply means “produced by synthesis”, or “made.” Synthroid and Estrace are “synthetic” in that they have been made in the laboratory rather than within a biological organism, but they are “natural” in that they’re the exact molecules made by the thyroid and ovary, respectively. Other examples of exact copies of our bodies hormones synthesized in the laboratory are Humulin® (insulin) and cortisone (cortisol).

So “natural” or bioidentical hormones are made in the laboratory, and the process is called “synthesizing.” Usually, the source of these “natural” human forms of ovarian hormones are the building blocks found in wild yams and soybeans. The laboratory converts these plant compounds into chemical molecules identical to those made in the human body for 17-beta estradiol, progesterone, or testosterone, which can then be fashioned into standardized tablets, patches, creams, gels and injectables for our prescriptions. Thus, we’re able to synthesize a natural, bioidentical compound to replace what our body no longer makes.

The flip side of this coin is that something “natural” may be foreign or “supernatural” for the human body. Consider Premarin: a “natural” mixture of estrogens made by a biological organism, the pregnant mare. But Premarin contains types of estrogen that are never found naturally in the human body. These estrogen types are more potent and more persistent than human 17-beta estradiol. In effect, Premarin is a “supernatural” estrogen for women that has some very undesirable consequences.

Another example is the “natural” estrogen-type compounds (genistein and others) found in soy and red clover and many other plants. These are “natural” substances, since they come from biological plant sources. These compounds are unnatural for our bodies, however, since we don’t make these same compounds and don’t have the enzymes to change the genistein or clover isoflavones into 17-beta estradiol.

These molecules act very differently at our body’s estrogen receptors, and don’t have the full protective effects of 17-beta estradiol on the heart, brain and bone. Furthermore, if you try to get enough active hormone from plant/herbal sources alone, it’s hard to determine how much you are taking and whether the amount is right for you, because plant/herbal sources aren’t standardized.

Don’t be misled by clever wording in advertising. While “natural” bears the mystique of being “better for you,” it isn’t always the case. If you aren’t sure about whether you should take natural or synthetic hormones, you might want to read more about it in Women, Weight and Hormones.

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