Oestrogen and Progesterone

Okay, so let's talk about the two main female hormones — estrogen and progesterone. We touched upon them briefly earlier when we talked about the menstrual cycle, but it’s really important to understand these two hormones and their key functions because they control all the major organs of the reproductive cycle. They also have a massive impact on other parts of female physiology. What’s important to understand about these two hormones is that they’re both essential, but they need to be in the right balance with one another. Most hormonal imbalances and most of the symptoms and conditions that I see in my practice are due to an imbalance between these two. Let’s start with estrogen. As we mentioned earlier, estrogen is the hormone active during the follicular phase — the hormone of growth and proliferation. In the menstrual cycle, it helps grow the uterine lining and thins the cervical mucus as we get closer to ovulation. There’s a surge just before ovulation that helps trigger the release of the egg. Estrogen is produced in the ovaries, but also in the brain and in fat tissue. This is important to understand, especially later on in perimenopause and menopause, when there are many misconceptions around estrogen production. It’s not just made in the ovaries; it’s made in other tissues too. Many tissues in the body have estrogen receptors, which means estrogen affects much more than just the reproductive system. Estrogen is made from testosterone through an enzyme called aromatase. As the hormone of growth and proliferation, it helps prepare the uterine lining for pregnancy and also helps trigger ovulation. When it’s balanced, estrogen is energizing and stimulating. This is why, in the first half of the cycle, many women feel more energized, confident, and driven — that sense of “get up and go.” However, if estrogen is out of balance or too high, it can lead to mood swings, anxiety, inflammation, and excessive growth in tissues. Because it’s a hormone of proliferation, excess estrogen can lead to things like cysts, fibroids, or a thick uterine lining that causes heavy bleeding or clotting. In more serious cases, excess estrogen activity can also be linked to tumor growth, as many tumors are estrogen-sensitive. So estrogen is essential — it should peak around ovulation — but it needs to be kept in check. The hormone that balances it is progesterone. Progesterone, as we saw earlier, is produced after ovulation from what’s left over of the egg, the corpus luteum. It helps maintain the uterine lining and keeps it stable for pregnancy. It’s also produced by the placenta during pregnancy. If fertilization occurs, the corpus luteum produces progesterone up until about ten weeks of pregnancy, after which the placenta takes over around week ten to twelve. This is why many miscarriages in the first trimester are linked to insufficient progesterone. Progesterone is made in the ovaries, womb, and adrenals, and it’s what I like to call the hormone of Zen. It’s calming, aids sleep, increases GABA (a calming neurotransmitter), and is powerfully anti-inflammatory. It’s also pro-metabolic and pro-thyroid. This is why your body temperature rises slightly in the second half of your cycle and why hunger and carb cravings often increase — your metabolism is ramping up. Progesterone helps relax smooth muscle, preventing uterine contractions. It’s also a potent antagonist to estrogen. I like to think of estrogen as the “naughty sister” — full of energy and sparkle but needing guidance — and progesterone as the wise older sister who keeps her in check. Neither one is good or bad, but balance is key. Progesterone is a direct estrogen antagonist and a natural cancer-preventive, anti-inflammatory hormone. It’s even been used in conditions like rheumatoid arthritis and in studies on brain injury recovery because of its calming and protective effects. In the second half of the cycle, progesterone helps you slow down and turn inward. It’s normal to feel a little less social or energetic during this time — it’s nature’s way of helping you conserve energy and protect yourself. But when there’s a major imbalance, symptoms can become more intense — low mood, anxiety, insomnia, night sweats, spotting, or PMS are all signs of insufficient progesterone or estrogen dominance. Another important thing to understand is that progesterone is the building block of cortisol, our main stress hormone. This is crucial because if the body must choose between producing cortisol (for survival) or progesterone (for reproduction), it will always prioritize cortisol. So chronic stress or constant cortisol activation can deplete progesterone and disrupt the balance between estrogen and progesterone — a key cause of many hormonal symptoms. To put it simply: estrogen is the builder, progesterone is the calmer. They work best together, like the lion and the lion tamer. What truly matters is the ratio between them. You can have low estrogen and even lower progesterone and still experience estrogen-dominant symptoms. It’s not just about the absolute levels — it’s about the balance. This balance is what I see most often disrupted in women’s health. We’ll explore later the common signs and symptoms of this imbalance, but for now, let’s move on to the other key hormones involved in the menstrual cycle — testosterone and cortisol.