happy-middle-aged-beautiful-woman1Bioidentical hormone therapy (BHT) is a big part of what we do at Ageology. If a patient is experiencing symptoms that have not been able to be cured with traditional medicine, we evaluate them to see whether a hormone imbalance exists. Then, we start low with bioidentical hormones, building slowly until we achieve symptom relief with ideal levels (which vary from person to person). We continue to meet with the patient over time, because their needs will change as their bodies change.

BHT for women is usually comprised of at least one of three hormones: estrogens (estriol and/or estradiol), progesterone and testosterone. Women who are premenopausal and experiencing symptoms related to lack of progesterone usually get progesterone only. The most common method for delivering progesterone is transdermally, through a cream applied to the skin.

It’s okay to get progesterone on its own, but we always give progesterone to women who receive estrogen. Without the balancing effects of progesterone, estrogen’s proliferative (tissue-growing) effects can raise the risk of cancer—most notably, uterine cancer.

The medical mainstream has a few stock arguments it throws out in opposition to BHT. One such argument usually goes something like this: “Transdermal progesterone isn’t absorbed in amounts high enough to protect the endometrium.” In other words, progesterone doesn’t move through skin and into the body in amounts adequate to protect against uterine cancer caused by estrogens.

In the best-known study to debunk this myth, Dr. Helene Leonetti and her colleagues gave 32 women oral progesterone or transdermal progesterone, plus the standard dose of Premarin (conjugated equine estrogens, the gold-standard estrogen replacement of that time). A placebo group got estrogen only. Testing of the women’s endometrial tissues found that the transdermal progesterone did protect the endometrium—despite the fact that the level of progesterone in the women’s blood serum remained quite low. Concentrations of progesterone of 5 pg/mL or greater are believed to be required for endometrial protection. Serum levels in Dr. Leonetti’s study didn’t even come close.

BHT proponents have long understood that this is because a blood test isn’t an accurate measure of progesterone absorbed through the skin. For reasons not yet understood, progesterone delivered through skin doesn’t move around the body in serum. It does show up in high concentrations in both saliva—which comes from glands with high blood flow, something like 10 times that of normal tissues—and capillary blood in the fingertips.

If one were to try to give enough transdermal progesterone to bring serum levels up to 5 pg/mL or more, an overdose would be the likely result. But if we measure levels in saliva or capillary blood, we see a rapid and adequate rise in progesterone levels within hours after application to the skin—more than adequate to protect the endometrium.

Now, a new study published in the scholarly journal Menopause elegantly addresses this ongoing controversy. One of its authors, David Zava, Ph.D., is the world’s best-known expert on this topic. He and his colleagues used both saliva tests and capillary blood tests to measure how well the hormone was absorbed through skin. They gathered 10 female subjects aged 51 to 61, with median age 58.5, and gave them progesterone cream or gel over a period of 14 days. Transdermal delivery reliably brought levels within the range known to protect the endometrium and balance the effects of estrogen. Capillary and salivary levels were 10-fold and 100-fold greater, respectively, than blood levels measured in these women.

Hopefully, this will help put the transdermal hormone delivery nay-sayers to rest. We also can deliver estradiol and testosterone transdermally, and the same rules apply: their absorption and distribution in the body can’t be reliably measured through a blood test. This is why Ageology recommends primarily salivary and capillary blood testing for the purposes of monitoring and prescribing BHT.


  • Leonetti HB, Wilson KJ, Anasti JN. Topical progesterone cream has an antiproliferative effect on estrogen-stimulated endometrium. Fertil Steril 2003; 79:221-222.
  • Du JY, Sanchez P, Kim L, Azen CG, Zava DT, Stanczyk FZ. Percutaneous progesterone delivery via cream or gel application in postmenopausal women: a randomized, cross-over study of progesterone levels in serum, whole blood, saliva, and capillary blood. Menopause, 20(11).

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