What You Need To Know About Estrogen & Progesterone: Is My Cycle Only Important for Fertility?
Updated: Mar 11, 2019
Estrogen and progesterone are the two main sex hormones produced by the ovaries, and both are essential for female health and wellness. For many women, the message they receive surrounding their hormones and monthly cycles is about its importance only in regards to fertility. That conversation is starting to change. As further research is focused on female hormones, and as we begin to understand more and more about the myriad of functions that both estrogen and progesterone play in the body, the importance of menstrual cycles – beyond strictly fertility – is being illuminated. In fact, the American College of Obstetricians and Gynecologists has recognized the menstrual cycle as a vital sign (along with blood pressure, heart rate, respiratory rate), which can provide important information for your overall health.
I strongly believe that education is empowerment, and I’m passionate about female empowerment, health and wellness so I couldn’t wait to write this article. Let’s dive in!
1. Understanding Your Cycle
Before we start talking about why estrogen and progesterone – and their balance – is so important, we first need to understand how these hormones change during the cycle each month. There are four main hormones involved: Follicle Stimulating Hormone (FSH) and Luteinizing Hormone (LH), which are produced in the pituitary gland (in the brain), and estrogen and progesterone which are produced primarily in the ovaries.
This is one of my favourite graphics showing cyclical hormonal fluctuations, what is happening in the ovaries, and what is happening in the uterus. As shown at the top, the female menstrual is divided into two phases: the Follicular Phase and the Luteal Phase. In the Follicular Phase, which starts on the first day of your period, FSH is secreted from the pituitary to stimulate the ovaries to do two things: firstly, to produce a follicle (which houses the egg or ovum) and secondly, to produce estrogen. Estrogen is the dominant hormone in this first half of the cycle, and functions to stimulate growth in the uterine lining (termed proliferative, at the bottom of the graphic).
As we approach mid-cycle, rising estrogen levels suppress FSH through a negative feedback loop, and begin to stimulate LH secretion through a positive feedback loop, ultimately resulting in an LH “surge”. The LH surge functions to tell the ovary to release the egg from the follicle – an important event termed ovulation. Typically, this occurs around day 14 of the cycle, but can be quite variable.
We are now into the Luteal Phase, which gets its name from the corpus luteum: the remnants of follicle which released the egg. It is an important structure that supplies the vast majority of the progesterone, which is the dominant hormone in the second half of the cycle. Progesterone is important for the maturation and maintenance of the uterine lining (termed secretory in the graphic) in preparation for pregnancy, and falling levels of progesterone near the end of the cycle are important for the shedding of the lining - menses.
2. Why are Estrogen and Progesterone Important?
While estrogen has been more thoroughly studied for its effects on bone, the cardiovascular system, breast health, and endometrial/uterine health, progesterone is starting to be understood as equally important. Rather, it’s the balance of these two hormones that is so essential. Our attention is often focused on menses – the period itself – but there is an equally important event occurring mid-cycle: ovulation. It is through ovulation that the corpus luteum is formed, and from this that the majority of our progesterone is secreted. If ovulation does not occur (termed anovulation), there is no corpus luteum, and progesterone is not produced. Therefore, it becomes clear that ovulation is essential for maintaining that crucial balance of estrogen and progesterone. Let’s look closer at some of the functions these hormones play:
For optimal bone health, both estrogen and progesterone are needed. Estrogen has long been shown to be important for bone health, and estrogen replacement therapy used for prevention of osteoporosis (1). So what about progesterone? A study headed by Dr. Jerilynn Prior (a pioneer in ovulation research) looked at the relationship between ovulatory disturbance and spinal bone loss. What her team found was that in women with at least 1 anovulatory cycle per year (where ovulation did not occur), spinal bone loss was about 4% per year. In those with multiple short luteal phases (remember that this is the second half of the cycle, where progesterone is produced), bone loss was 2% per year. And in women with regular, ovulatory cycles their spinal bone density remained the same. That is a 20% change in bone loss related to progesterone! (2,3)
The bottom line: we need progesterone – and ovulation – in addition to estrogen in order to maintain healthy bone.
**I’ll be writing an article soon about what this means in the various stages of life soon – stay tuned!
Cardiovascular health is another area in which estrogen has gotten a lot of attention, while progesterone has remained somewhat elusive. Estrogen therapy is supported by a large body of research as being protective of coronary artery disease (4), and we are now beginning to understand the importance of progesterone. For example, one animal study has shown that when ovulation is suppressed (and progesterone levels lower) due to stress, the incidence of atherosclerosis was greatly increased. Additionally, LDL-cholesterol levels were higher when ovulation was suppressed (5). Progesterone has also been shown to be an important factor for vascular endothelial function – the mechanism that causes blood vessel dilation and affects blood flow (an important part of cardiovascular health), and is equally as effective if not better than estrogen at increasing blood flow (6).
The bottom line: both progesterone and estrogen are important for heart health. Non-ovulatory cycles and progesterone deficiency can negatively affect heart health.
A common sign of what is termed “estrogen dominance” is cyclical breast tenderness of fibrocystic breasts. Estrogen dominance can occur when estrogen levels are overtly high, or when progesterone levels are low (creating an imbalance in the ratio of these hormones). Studies have shown progesterone to be lower in women who suffer from these conditions (8). What is perhaps even more striking is the incidence of breast cancer in women with progesterone deficiency: premenopausal breast cancer risk has been found to be considerably increased (up to 5 times) in women with hormone-related infertility (9) – that’s a scary thought. Natural progesterone (as opposed to synthetic progestins) has been shown to be protective and progesterone therapy is being investigated for prevention of breast cancer (10).
The bottom line: endogenous (made by your own body) progesterone is important in both benign breast conditions and in breast cancer prevention.
ENDOMETRIAL HYPERPLASIA & CANCER:
Earlier, I discussed the function of estrogen in stimulating growth of the endometrium (uterine lining) and progesterone in its maturation. The fall of progesterone near the end of the cycle is also important for shedding the endometrium each month. Without the rise and fall of progesterone, endometrial growth can go unchecked, leading to an overgrowth termed endometrial hyperplasia. Progesterone is important to antagonize the proliferative action of estrogen. Insufficient progesterone levels have also been linked to dramatically increased risk of endometrial cancer(11). Interestingly, researchers have begun to look at intrauterine progesterone in the treatment of low-grade endometrial cancer, with promising results (12).
The bottom line: monthly cyclical progesterone levels are necessary for the cyclical shedding of the endometrium and prevention of endometrial cancer
3. What Can Affect Your Hormones and Cycles
So now we know how important the balance of estrogen and progesterone are, not only for fertility (which is important!), but also for bone health, heart health, breast health, and endometrial health (there are many other functions I haven't even gone into!). We know, too how vital ovulation is for progesterone production, and maintaining that hormonal balance. With this knowledge in mind, the next step is to understand what could potentially be disrupting ovulation, hormone production, and monthly cycles. Here are some of the most common reasons (outside of pregnancy):
Silent anovulatory cycles:
Intermittently, many women can have cycles which appear completely normal, but where ovulation has not occurred. One study (13) showed that anovulation occurred in over a third of clinically normal menstrual cycles – 37% !! These don’t look different from an ovulatory cycle, so it can be difficult to determine (hence the term “silent”). Keep reading to find out how you can tell if you’re ovulating.
Long Cycles (oligomenorrhea) or Missed Periods (if >3, amenorrhea):
Hypothalamic Amenorrhea (HA): this is a common and reversible condition in which the brain no longer signals the ovaries to produce estrogen, resulting in anovulation and no period (14). This is generally due to some kind of stress, where the body goes into survival mode and shuts down reproduction. Some of the more common causes of HA are
Lack of nutrition
Polycystic Ovary Syndrome (PCOS): see my previous post about PCOS. What is important to recognize is that PCOS does not go away after childbirth or menopause, and it may put women at risk to develop metabolic syndrome, diabetes, and cardiovascular disease.
Hyperprolactinemia: this is a condition of elevated prolactin, which can disrupt the normal communication of the brain (by suppressing a hormone called GnRH) and ovaries. It can occur due to
Prolactinoma (a pituitary tumor)
Premature Ovarian Insufficiency (POI): essentially, this refers to early menopause. In women under 40 years old who experience many of the signs and symptoms of menopause, POI may be the cause (15).
Hormonal contraception introduces synthetic estrogens and progesterone (progestins), which can suppress ovulation. Obviously, this suppression leads to decreased progesterone production. It is important to note that synthetic progestins do not act identically to endogenous or bioidentical progesterone in the body.
Combined oral contraceptive pills as well as Depo-provera will affect ovulation, while a low-dose progestin IUD (Mirena, Kyleena, Jaydess) is much less likely to alter ovulation (however, research is lacking around its effects on ovulation over time).
4. How Do I Know if I’m Ovulating?
Know Your Cycle:
The first step I generally recommend for women who have never done any cycle charting is simply to become familiar with their cycle. This can include tracking the first day and length of your menstrual bleed, as well as symptoms you experience throughout your cycle such as breast changes, bloating, cramps, mood shifts, and energy levels. This can be done on your calendar, or with easy to use apps such as Kindara, Clue, and Monthly Cycles.
Basal Body Temperature (BBT) Tracking:
This is a step up from tracking your cycle and while it is somewhat more involved, it gives you a whole lot more information! Progesterone causes your morning basal body temperature to rise slightly (typically less than 0.5F or 0.3C), so by tracking your daily temperature and looking for a pattern similar to the one below, you will be able to see when you have ovulated (and started to produce more progesterone). It also provides a reliable method for assessing the length of your luteal phase (the second part of your cycle) (16).
I recommend to use a thermometer that has 2 decimal places for accuracy, and taking your temperature reading first thing in the morning (ideally, before getting out of bed). BBT tracking can also be done with a charting sheet (a sample charting sheet is available here), or with one of the apps listed above.
And here is a fantastic resource put out by a group of the University of British Columbia with more information on BBT.
One of my very favorite medical terms, this word of German origin refers to the “twinge” of pain some women experience when ovulating. Not all women can feel this (and that’s perfectly normal!), however some women may feel anything from a gentle sensation to a more substantial cramp on one side of the lower abdomen, approximately mid-cycle, signalling ovulation.
Cervical mucous and height:
This is a fantastic way to become more familiar with your anatomy and what is happening cyclically! Around ovulation, vaginal secretions change from infertile to fertile in order to become more habitable for sperm. This fertile cervical mucous is creamy, sticky and stretchy with an egg-white like consistency, and can often be seen as discharge. After ovulation, these secretions become more infertile (drier).
Additionally, cervical anatomy changes slightly as well. I was taught the acronym SHOW for a fertile cervix, which stands for soft – high – open – wet. The texture of the cervix is often described as the tip of your nose, however it becomes somewhat softer during ovulation. Your cervical height does raise, it opens slightly, and due to the cervical mucous, it will be wetter. For the adventurous, yes you can feel these changes! If you are so inclined to acquaint yourself with this part of your anatomy, with some practice you will be able to feel the change from infertile (firm, low, closed, dry) to fertile.
Ovulation Prediction Kits (OPKs) are used to detect the LH surge that occurs just prior to (usually about 36 hours before) ovulation. These are urine tests (which are available at most pharmacies and drug stores), which measure the amount of Luteinizing Hormone in the urine in order to predict ovulation. Do note that they do not confirm ovulation, but do confirm the LH surge (which is typically – though not always – followed by ovulation)
Day 21 Progesterone:
Having your progesterone tested via a blood sample on approximately day 21 of your cycle can help to confirm ovulation. In women who ovulate mid-cycle (on day 14), progesterone levels peak around day 21. However, it can be a bit of a moving target as many women don’t ovulate exactly mid-cycle. Therefore, I find it’s best when used in combination with BBT tracking and/or OPKs. Beyond this simple test, there are several month-long hormone panels (salivary and urinary) that can be used to investigate hormonal fluctuations and confirm ovulation.
5. How can I take charge of my female health?
First and foremost, tune in to your body. Your cycle is yours to explore and develop mindfulness of. By adopting some of the practices above, we can learn a lot about our bodies and cycles. I believe that even this simple act of bringing our attention to our cycle can affect hormonal fluctuations.
Next, find a health care practitioner you are comfortable with. If you suspect that your hormones may be out of balance and you may be experiencing anovulatory cycles, it is so important to have a proper workup done (including an investigation into your health history and hormone testing) to identify the root cause of the hormonal imbalance and treat accordingly. If you’d like to discuss your hormones and treatment options, consider booking an appointment at Juniper Family Health.
Wishing you health and well-being!
1. Stefanick, M. et al. (2003). The Women’s Health Initiative Postmenopausal Hormone Trials: Overview and Baseline Characteristics of Participants. Ann Epidemiol, 13:S78-S66.
2. Prior, J. et al. (1990). Spinal bone loss and ovulatory disturbances. New England Journal of Medicine, 1;323(18):1221-7.
3. Prior, J. (1990). Progesterone as a bone-trophic hormone. Endocrin Rev, 11(2): 386-398
4. Subbiah, M. (1998). Mechanisms of Cardioprotection by Estrogens. Experimental Biology and Medicine, https://doi.org/10.3181/00379727-217-44201
5. Adams, M. et al. (1985). Ovariectomy, social status, and atherosclerosis in cynomolgus monkeys. Arteriosclerosis, 5(2): 192-200.
6. Molinari, C. et al. (2000). The effect of progesterone on coronary blood flow in anaesthetized
Pigs. Experimental Physiology, 86(1): 101-108
7. Mather, K. et al. (2000). Preserved Forearm Endothelial Responses with Acute Exposure to Progesterone: A Randomized Cross-Over Trial of 17-β Estradiol, Progesterone, and 17-β Estradiol with Progesterone in Healthy Menopausal Women. The Journal of Clinical Endocrinology & Metabolism, 85(12): 4644-4649.
8. Sitruck-Ware, R. et al. (1979). Benign breast disease I: hormonal investigation. Obstetrics and Gynecology, 53(4): 457-460.
9. Cowan, L. et al. (1981). Breast cancer incidence in women with a history of progesterone deficiency. American Journal of Epidemiology, 114(2): 209-217.
10. Lieberman, A. and Curtis, L. (2017). In Defense of Progesterone: A Review of the Literature. Alternative Therapies, 23(6)14-22.
11. Kim, J. et al. (2013). Progesterone Action in Endometrial Cancer, Endometriosis, Uterine Fibroids, and Breast Cancer. Endocrine Reviews, 34(1): 130-162.
12. Montz, F. et al. (2002). Intrauterine progesterone treatment of early endometrial cancer. American Journal of Obstetrics and Gynecology, 186(4): 651-657.
13. Prior, J. et al. (2015). Ovulation Prevalence in Women with Spontaneous Normal-Length Menstrual Cycles – A Population-Based Cohort from HUNT3, Norway. PLoS One, 10(8): e0134473.
14. Shufelt, C. et al. (2017). Hypothalamic Amenorrhea and the Long-Term Health Consequences. Seminars in Reproeuctive Medicine, 35(3): 256-262.
15. Nelson, L. (2009). Clinical practice. Primary ovarian insufficiency. New England Journal of Medicine, 360(6): 606-614.
16. Prior, J. et al. (1990). Determination of luteal phase length by quantitative basal temperature methods: validation against the midcycle LH peak. Clin Invest Med, 13(3): 123-131.