Progesterone - The Natural Protector

Progesterone - The Natural Protector

This article is about Natural Progesterone and how it protects against hormonally driven oestrogen responsive cancers like breast cancer and prostate cancer; and has effects against a low thyroid hormone levels, stress, osteoporosis, endometriosis and menopausal symptoms.

Its only natural

Natural Progesterone should not be confused (but often is) with synthetic alternatives, which have been linked to an increased risk of breast cancer in women. (Article written by Chris Woollams, M.A. (Oxon), Biochemistry).

In a Nov 2017 review by Allan Lieberman et al (1) They concluded, "Physicians should have no hesitation prescribing natural progesterone. The evidence is clear that it does not cause breast cancer. Indeed, progesterone is protective and preventative of breast cancer."
Progesterone ~ The Natural Protector

Cotton vs Nylon

The confusion between natural progesterone and synthetic arose during the Women's Health Initiative in the USA which ran from 1997 to 2005. Within this, one trial looked at HRT. One group of women took oestrogen-only HRT, while a matched group took oestrogen + progesterone HRT.

The trial was stopped early (2). The mixed HRT suddenly had double the number of cases of breast cancer. 

The oestrogen-only group was allowed to continue, it had 'only' seen a 27 per cent increase.

The only difference between the two groups was the progesterone - it was SYNTHETIC PROGESTERONE.

The media coverage of the study caused widespread fear of HRT in the USA, with many stopping its use. Further media coverage showed this resulted in falling breast cancer rates, for the first time ever. While the subgroups in the WHI study were quite small, the research was confirmed by a much larger study, namely Cancer Research UK's Million Women Study. Here scientists found that women using combination HRT were twice as likely to develop breast cancer as non-users.

Many people (doctors included) get completely confused between synthetic progesterone and natural progesterone. They are as different as two shirts, one made of nylon and the other of cotton. Synthetic progesterone, in fact, should not be even called progesterone by the media. Its name in the UK is progestagen and in the USA, progestin.

For example, Megastrol Acetate (Megace) is a drug - a synthetic progesterone - used to treat a number of conditions including weight loss in people with cancer or HIV, or men with swollen prostates, or women with endometriosis. It is recommended that it should not be used by women who are pregnant and has numerous side-effects such as nausea, unexpected vaginal bleeding, and impotence in men.

None of this applies to Natural Progesterone! The man-made equivalents are widely used.  The important thing to understand is that these synthetic hormones are similar to, but not identical to, natural progesterone. And that's the problem; even slight changes to hormones can, and do, cause considerable differences once in the human body.

Natural progesterone, the menstrual cycle and pregnancy

Progesterone is a steroid hormone produced by the female ovary immediately after ovulation. It prepares the womb to accept the egg and prevents muscle contractions in the womb avoiding rejection of the egg. During pregnancy, levels rise from week 9 to week 32. The placenta will also make progesterone from week 12 to keep baby healthy. So, natural progesterone helps maintain the menstrual cycle, and maintains pregnancy (3).

Within this are more clues as to its function - for example it increases vascularistation (blood supplies to the womb lining, or endometrium) and is an important part of bone production. 

Progesterone and Bone Health

According to American Bone Health website, in healthy bones, Osteoclasts help to break down old bone tissue, while osteoblasts stimulate new bone growth. Oestrogen has a rate limiting effect on Osteoclasts, so it slows the breakdown of old bone, but has little effect or no effect on osteoblasts. So oestrogen gets in the way of bone health! 

To the contrary, Progesterone stimulates osteoblast cells to form new bone tissue and it does this more effectively than any other protocol, including aerobic exercise!

Research has also shown that the contraceptive pill containing synthetic progesterone can damage bone health in adolescents (4).

Progesterone and Stress

Progesterone is also produced in the adrenal cortex and plays an important role in reducing stress (5). 

Progesterone and Endometriosis

Mice given natural progesterone before any lesions developed had far less lesions ultimately (14). Natural Progesterone restricts the formation of new blood supplies, reduces oestrogen levels and inflammation. It has been shown several times to reduce the lining and the spread of endometriosis.

Progesterone and blood pressure

Weill Cornell researchers have shown that your natural progesterone limits high blood pressure (6). According to Dr. Lawrence Resnick, progesterone is a vasoactive hormone that directly affects blood vessels.

Progesterone and your Thyroid

Progesterone actually improves thyroid function; it can improve thyroid levels, improve energy, and helps its uptake by cells in the body (13). When oestrogen levels in the body are high, they prompt the liver to make more thyroid binding globulin, and so free thyroid hormone declines and Hypothyroidism can result. High oestrogen, low thyroid hormone, can result in hot flushes.

Patients may not need that synthetic thyroid hormone, because they are actually making the correct amount. If they reduced their oestrogen, blood levels would return to normal.

And the way to do that? Increase natural progesterone.

Progesterone and Men

It is important to understand, that progesterone is not a feminising hormone. Progesterone is also produced by the testes; in men and has significant benefits. Not least, it keeps oestrogen in check!

     * It inhibits 5-alpha reductase, which converts testosterone into the more aggressive DHT (7)

     * It inhibits noradrenaline in men; this stress hormone can limit libido.

     * Progesterone can improve sperm counts - oestrogen and xenoestrogen, reduce them (8)

     * Progesterone is involved in a good night's sleep

     * Progesterone is involved in bone mass for men, not just women

     * Progesterone can reduce high blood pressure in men too.

Inhibitors of Natural Progesterone

Is it important to have good levels of progesterone? A 30 year retrospective study at John Hopkins University showed conclusively that women who were progesterone deficient had 5.4 times the level of breast cancer and 10 times more deaths from cancers of all types. (9).     

     * Stress and the production of cortisol by the adrenal glands can diminish natural progesterone levels. 

     * Poor diet and lifestyle have made periods far more irregular for women and, although a woman may bleed, she may not have ovulated. She may make far less actual progesterone across the average year than nature intended.

     * One of the major evolutionary functions of natural progesterone is to balance and oppose oestrogen. After ovulation the ovaries produce approximately 20 mg per day of progesterone, stopping any further oestrogen-induced ovuiations. During pregnancy the placenta produces more than 300 mg of progesterone per day for similar reasons. Indeed Cancer Research UK has shown that breast cancer rates fall the more children a woman has. A move to less children, will see less lifetime progesterone production.

     * Progesterone may naturally decline in women who make higher oestrogen, or increase levels of xenoestrogens (herbicides, pesticides. or everyday toiletries such as nail polish - eg. containing toluene - and perfumes). High testosterone may reduce levels too.

Progesterone - other benefits

Progesterone has receptor sites in bone cells, nerve sheaths and in brain cells indicating that it plays a role in all their functions.

There are two or three scientific clinical trials (e.g. Smith, Gung, Hsu - Nature 1998 and Magill P, Br.-J Gen Pract; Nov 1995) that imply it will help in PMS.

Progesterone and menopause

Menopause is not something that happens suddenly. From the age of 35 most women's progesterone levels start to decline as they gradually stop ovulating or "splutter" out of eggs (significant levels of progesterone are only produced from the empty follicle after a women ovulates).

At these times the adrenals are the sole source of the natural hormone, but only producing 3 per cent of the original amount. Indeed less progesterone than is normally produced by a man.

On the other hand, oestrogen levels can remain high right up until menopause when they will decline to approximately 40 - 60 per cent of original levels, just enough to stop ovulation (oestrogen is also the hormone that builds up the womb lining).

Open quotesMenopause symptoms are not because of low oestrogen - but because of extremely low progesteroneClose quotes

Thus oestrogen is still produced in quite large quantities (it is also made in muscles for example) yet progesterone is drastically reduced. Couple this with the effects of certain herbicides, pesticides or toiletry ingredients, which are known to mimic the action of oestrogen in the body, and a woman can suddenly experience severe oestrogen dominance. And excess oestrogen is linked to an increased risk of cancer.

The balance between oestrogen and progesterone poses other questions. For example, if osteoporosis is a condition of the menopause when oestrogen declines, why are so many women with regular cycles reaching menopause with osteoporosis well underway? As we showed above, one counter argument is that the bone building benefits of progesterone have been severely hampered over time by the synthetic versions in the pill, or other synthetic oestrogen providers.

Hot flushes can occur when the oestrogen is declining around the age of menopause when a woman is having anovulatory cycles (not ovulating) and the follicle stimulating hormone is working like fury trying to squeeze any last drop of oestrogen from the ovaries.And the balance of oestrogen to progesterone has dramatically changed.

Is the solution to increase your oestrogen further by taking HRT, or is it to try to maintain the original balance by increasing natural progesterone instead?

Open quotesWhy are so many women with regular cycles reaching menopause with osteoporosis already well underway?Close quotes

That high levels of oestrogen are ever present in women is all too clear to scientists if not to doctors. One study on oestrogen confirmed that overweight post-menopausal women actually have higher oestrogen levels than thin pre-menopausal women, thus exploding the myth that somehow your oestrogen levels have declined dramatically! Moreover, the new aromatase inhibitor drugs have been designed to cut high oestrogen levels in post-menopausal women. Now, I thought doctors had been dishing out HRT because post-menopausal women had so little oestrogen - silly me.

Breast Cancer - progesterone protects

The late Dr Paul Layman wrote to us to clear up errors in an interview with breast cancer Professor Tony Howell made during an interview with CANCERactive. Paul wrote, "An eighteen year study on the protective effect of natural progesterone has recently been confirmed. And another study on the oestrogen receptor status of breast cancer is now thought to be of significance in recurrence rates.

Importantly, an Imperial Cancer Research Fund study seemed to suggest that the timing of breast surgery was more important than receptor status".

At CANCERactive we have covered this in our magazine icon: 'Choosing the correct point in your monthly cycle to have a breast operation can increase your 10-year survival by two thirds!' Every woman and their doctor should know this research.

"Women having breast tumours removed during the follicular phase of their cycle (that is days 3-12 when their oestrogen is high) have a 10-year survival rate of only 45 per cent, compared to a 10-year survival rate of 75 per cent for women having surgery during the luteal phase (when progesterone is high)."

Indeed the research also showed that oestrogen receptor positive and progesterone receptor positive tumours had the highest survival rates if surgery was performed in the second half of a woman's cycle.

This work actually confirmed an earlier study (10) from Guy's Hospital in August 1999 and yet earlier work by Hrushesky et al (Lancet 7989). 

They all found the same thing - surgery for breast cancer, when progesterone levels are highest, is more protective!

A further study (11) shows that natural progesterone actually inhibits growth and induces cell death in breast cancer cells by affecting p53 and Bcl-2 gene expression.

This followed studies (12)  by Pak Chang, and others at Weill Cornell showing that, while oestradiol (the most potent oestrogen hormone) increased the number of circulating epithelial cells, natural progesterone actually decreased them.

This study further states that natural progesterone secretion suppresses oestradiol receptors in both the endometrium and breast tissue, and has an anti-oestrogen effect (just as, for example, the latest aromatase inhibitors aim to do), but that very high concentrations of synthetic progestins can stimulate human breast cancer cells.

Which takes us back to where we started. Cotton is good, nylon certainly isn't.

Obtaining natural Progesterone

Natural progesterone is available as a cream or as pills, tablets and as a pessary, but has to be prescribed. Check out the possible benefits of natural progesterone - and make sure neither you, nor your doctor are confused between cotton and nylon.

For further help and information, you could contact Judy Evans, UK expert on Natural Progesterone at [email protected]

Tel - 01935 474343 

Go to: 10 other ways to reduce oestrogen naturally


1. In Defense of Progesterone: A Review of the Literature - Alt Ther Health Med; 2017 Nov;23(6):24-32; Alan Lieberman, Luke Curtis. -  

2. Second long term HRT trial stopped early; BMJ 2002 Nov 2; 325(7371): 987; Caroline White - 

3. The University of Rochester Medical Center; Health Enclycopedia, Progesterone

4. Hormonal Contraception and Bone Health in Adolescents; Front Endocrin (Lausanne); 2020; 11: 603.

5. Weill Cornell, Progesterone, not just a sex hormone -

6. Histories of abuse predict stronger within-person covariation of ovarian steroids and mood symptoms in women with menstrually related mood disorder; Psychomeuroendocrinology, 2016 May;67:142-52.  doi: 10.1016/j.psyneuen.2016.01.026. Epub 2016 Feb 1.

7. Lee, J. “Prostate disease and hormones.” The John R. Lee, M.D. Medical Letter Feb. 2002. Laura A. Bachrach. 

8. A relationship between sperm count and intracellular progesterone, 17 alpha-hydroxyprogesterone, and cortisol concentrations in human spermatozoa; Fertil Steril, 1994 May;61(5):990-2. -  

9Breast cancer incidence in women with a history of progesterone deficiency; Am J of Epidem; 1981 Aug;114(2):209-17.

10. Survival of Premenopausal Breast Carcinoma Patients in Relation to Menstrual Cycle Timing of Surgery and Estrogen Receptor/Progesterone Receptor Status of the Primary Tumor; Cooper, Gillett, Patel, Barnes and Fentiman;

11. Formby, B. and Wiley, T.S. Progesterone Inhibits Growth and Induces Apoptosis in Breast Cancer Cells: Inverse Effects on Bcl-2 and p53. Ann Clin Lab Science. 1998 Nov-Dec;28(6):360-9.

12. Pak Chang, Lee et al. Fertility and Sterility vol 63; Weill Cornell

13.  Progesterone therapy increases free thyroxine levels--data from a randomized placebo-controlled 12-week hot flush trial; Sathi, P. et al.  Clin Endocrine, 2013 Aug;79(2):282-7.

14. Progesterone Alleviates Endometriosis via Inhibition of Uterine Cell Proliferation, Inflammation and Angiogenesis in an Immunocompetent Mouse Model; PLOS ONE, Oct 24, 2016;

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