How Science Got It Wrong About Progesterone

Progesterone is important for women's health.

Progesterone has been both ignored and mistakenly blamed for side effects it does not cause. How did that happen?

First, progesterone was discovered after estrogen, so, according to endocrinology professor Jerilynn Prior, missed being part of the tidy hormone dichotomy of “testosterone for men and estrogen for women.”

Next, progesterone could not (at first) be made into a medication because it could not be absorbed orally. Therefore, progesterone missed out on the hormone gold rush that was happening with “the estrogen-discovering scientists, estrogen-treating clinicians and estrogen-making pharmaceutical manufacturers.” By the time progesterone could be made into a medication (with the invention of oral micronized progesterone), it was too late; progesterone was left behind.

Finally, because progesterone could not (at first) be made into a medication, it was replaced by synthetic progestins in research and treatment. Unfortunately, progestins have different (and sometimes opposite) effects than progesterone, and (sadly) many of the side effects and risks of progestins have been mistakenly attributed to progesterone. For example, progestins increase the risk of breast cancer, but progesterone reduces the risk.

Estrogen and progesterone work together to build long-term health

It’s time to bring progesterone back into the conversation because estrogen and progesterone together work as a team. For example, the pre-ovulatory surge of estrogen (estradiol) is necessary for ovulation and the manufacture of progesterone. Estrogen also works in every tissue to promote progesterone receptors.

In turn, progesterone counterbalances estrogen in all parts of the body, including:

  • the uterus, where progesterone thins the lining while estrogen thickens it
  • the brain, where progesterone is calming while estrogen is stimulating
  • the breasts, where progesterone helps to slow cell division, while estrogen increases cell division.

Progesterone can also promote ovulation in a subsequent cycle by providing important hormonal feedback to the brain.

👉🏽 Did you know? On a blood test, a good peak luteal phase progesterone level is 80 nmol/L, 100 times more than an average peak estradiol level of 800 pmol/L (0.8 nmol/L).

Together, estrogen and progesterone promote the long-term health of the brain, bones and cardiovascular system. As Professor Prior explains: “ovulatory cycles across a woman’s long reproductive life span are needed to prevent osteoporosis and fracture, heart attacks, and breast and endometrial cancers during women’s older years.”

In other words, every ovulatory cycle is like a deposit into the bank account of long-term health.

Estrogen and progesterone for long-term health.

Do you make progesterone?

A regular ovulatory menstrual cycle is the only way to make progesterone.

Definition: An ovulatory cycle is a menstrual cycle in which basal body temperatures go up with ovulation and stay up for at least eleven days, indicating a healthy luteal phase.

A cycle without ovulation or progesterone is called an anovulatory cycle and is common. Read Ovulation is the main event of the menstrual cycle.

👉🏽Tip: Knowing if and when you ovulate is called body literacy.

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