Why Progesterone is Just as Important as Oestrogen for Women’s Health

According to Canadian endocrinology professor Jerilynn Prior in her paper titled "Women's reproductive system as balanced estradiol and progesterone actions," it's time to start discussing progesterone in the context of women's health. Professor Prior argues that historically there has been too much emphasis on oestrogen while progesterone has been overlooked or unfairly associated with negative effects. This oversight and misattribution of side effects to progesterone may have been due to the fact that progesterone was discovered after oestrogen and missed out on being part of the ideal hormone dichotomy of "testosterone for men and oestrogen for women."

Initially, oral absorption of early progesterone preparations was poor, rendering the hormone uninteresting to "oestrogen-discovering scientists, oestrogen-treating clinicians, and oestrogen-producing pharmaceutical manufacturers" who operated in tandem. However, modern oral micronised progesterone preparations can be effectively absorbed.

Furthermore, synthetic progestins rapidly superseded progesterone in both research and treatment, despite progestins having differing and occasionally opposing effects compared to progesterone. As a result, side effects and risks associated with progestins were mistakenly attributed to progesterone. For example, progestins have been linked to a higher risk of breast cancer, while progesterone has been shown to reduce the risk.

Oestrogen and progesterone are the two primary ovarian hormones in women, and they work in tandem to foster long-term health. For instance, the pre-ovulatory surge of oestrogen (estradiol) is necessary for ovulation and the production of progesterone. Oestrogen also promotes progesterone receptors in every tissue.

Progesterone plays a balancing role against oestrogen throughout the body, including in the uterus, brain, and breasts. In the uterus, while oestrogen thickens the lining, progesterone thins it out. Conversely, while oestrogen is a stimulant in the brain, progesterone is calming. Additionally, progesterone slows cell division in the breasts, whereas oestrogen increases it. Moreover, progesterone's hormonal feedback to the hypothalamus can promote ovulation.

Fun fact: A good peak luteal phase progesterone level is 80 nmol/L, which is 100 times greater than an average peak estradiol level of 800 pmol/L (0.8 nmol/L) on a blood test.

Oestrogen and progesterone work together to promote the long-term health of the brain, bones, and cardiovascular system. As Professor Prior notes, "normally 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." Each ovulatory cycle contributes to long-term health, much like a deposit into a bank account.

The Role of Oestrogen and Progesterone in Maintaining Long-Term Health and the Importance of Adequate Progesterone Levels.

Did you know that the only way to produce sufficient amounts of progesterone is by having a regular ovulatory menstrual cycle? This means that during your menstrual cycle, your basal body temperatures should rise with ovulation and remain elevated for at least 11 days, indicating a healthy luteal phase.

If you experience ovulatory disturbance (indicated by a short luteal phase), anovulatory cycles (indicated by no luteal phase or temperature rise), or use hormonal birth control (as most types suppress progesterone and contain no progesterone), you may develop progesterone deficiency.

Fortunately, progesterone levels can be tracked and addressed through various methods, including tracking ovulation with temperature readings and/or using an at-home progesterone test. This approach, known as body literacy, is essential to identifying and treating progesterone deficiency.

In her paper, Professor Prior emphasises the importance of recognising and restoring progesterone levels, stating that it is crucial to promote long-term health and prevent a range of health issues, including osteoporosis, fracture, heart attacks, breast and endometrial cancers, particularly in older women.

In cases where progesterone is low, it can be restored along with ovulation by taking measures to reduce stress, ensuring proper nutrition, and promoting overall health. 

According to the American College of Obstetricians and Gynaecologists (ACOG), ovulation is a reflection of general health, or a "monthly report card." If ovulation cannot be restored through lifestyle changes, cyclic progesterone therapy can be used as a viable treatment for conditions such as PCOS, irregular cycles, and heavy bleeding during perimenopause.

In more recent studies women with healthy levels of progesterone are shown to be more resilient in perimenopause.

Progesterone Post Menopause and after Hysterectomy.

Progesterone is no longer just associated with the uterus, as the medical community has started to recognise its value beyond the endometrium. Progesterone plays an important role in many critical central nervous system functions, and the significant drop in progesterone levels that follows bilateral oophorectomy can have a notable impact on mood, cognition, and neurogenesis. Various studies have found convincing evidence of progesterone's neuroprotective effects. One research cohort from the University of Southern California notes that progesterone therapy is an important area of investigation because the non-reproductive functions of progesterone receptors have extensive implications for hormone therapy that maintains neurological health and function throughout menopausal ageing.

Recently, emerging evidence has suggested a possible link between progesterone and emotional health after menopause through the gut-brain axis. A 2019 study on mice led Japanese researchers to conclude that progesterone could reduce depression and anxiety by changing the gut microbiota composition, particularly by increasing the Lactobacillus spp. population. Although more research is necessary to confirm this connection, it provides an interesting argument for using progesterone treatment after hysterectomy with oophorectomy.

The evidence supporting progesterone treatment after surgical menopause is increasing and convincing, and so far, no well-documented risks have been linked to its use. It's essential to remember that while combined oestrogen-progestin therapy has been linked to an increased risk of breast cancer, Oestrogen-progesterone combination therapy has not. However, whether or not progesterone treatment is necessary depends on individual symptoms, goals, and priorities.

DISCLAIMER: This article does not constitute as medical advice, and is for informational purposes only. It is not intended to be a substitute for professional medical advice and should not be relied on as health or personal advice.

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