On Estrogen: The Hormone Doing Most of the Talking
A journal entry on what she is, what she does, and the quiet conversations she keeps with everything else.
Ask anyone what estrogen does, and the answers tend to land in the same small territory. Periods. Pregnancy. Menopause. Some version of the female hormone.
The actual territory is much larger.
Estrogen is the loudest hormone of the cycle, the one with the widest reach, and the one most often misunderstood. She is what people mean when they say hormonal. She is blamed for the bad days, occasionally credited for the good ones, and rarely thanked for the work she does in your bones and your brain and your blood vessels every hour of every day.
So let us spend a little time with her.
What estrogen actually is
Estrogen is not one molecule but a family — three of them, in most accounts, with a fourth that appears only in pregnancy. They are all built from cholesterol. They are all related. They are all reading from the same general script. But each takes the lead at a different chapter of a woman's life, and each has its own potency, its own moment, and its own dominant source in the body.
The three to know are estradiol, estrone, and estriol — often shortened to E2, E1, and E3. The numbers are simply names; they refer to small differences in chemistry that you do not need to memorize.
Meet the three
Estradiol (E2) is the main character of the reproductive years. She is by far the most potent of the family — many times stronger than her sisters at the cellular level — and she is what people mean when they say "estrogen" without specifying. She is made primarily by the ovaries, specifically by a layer of cells called the granulosa cells that surround each developing follicle, and she rises and falls in the rhythm of the cycle. Most of what you feel of estrogen, you are feeling of her.
Estrone (E1) is the quieter sister. She is weaker than estradiol but more enduring. She is made mostly in fat tissue, through a process called peripheral conversion, in which an enzyme called aromatase turns androgens — including testosterone — into estrogens. During the reproductive years, she sits in the background. After menopause, when the ovaries quiet down, she becomes the dominant form — the body's way of continuing the conversation, more softly.
Estriol (E3) is the pregnancy estrogen. The placenta produces her in remarkable quantities once a pregnancy is established, with levels rising hundreds of times above their non-pregnant baseline. Outside of pregnancy, she is present in only trace amounts.
There is also estetrol (E4), made by the liver of the fetus, and only during pregnancy. She has recently begun appearing in a few newer hormonal contraceptives, which is the most likely place a person would encounter her name. For most purposes, she is a footnote.
Where she comes from
Estrogen begins, like most steroid hormones, as cholesterol. The body modifies this molecule through a series of small chemical steps — first to pregnenolone, then to progesterone or to androgens such as testosterone, and finally, through the enzyme aromatase, to estrogen itself.
Aromatase is a name worth holding onto. It comes up in cancer treatment, in PCOS, in hormonal contraception, in perimenopause. It is essentially the gate through which testosterone becomes estradiol. Many medications used to lower estrogen levels work by blocking aromatase.
The ovaries do most of this work during the reproductive years, specifically the granulosa cells around each developing follicle. But the ovaries are not the only source. Estrogen is also made in the adrenal glands in small amounts, in fat tissue through aromatase activity, in the placenta during pregnancy, and even, in trace amounts, in the brain, the bones, and the skin.
This wide manufacturing base is part of why estrogen reaches into so many systems. It is being made, quietly, in many of them.
What she does
Almost everywhere in the body, there is a receptor waiting for her.
Estrogen receptors come in two principal forms — called ER-alpha and ER-beta — and they are distributed in different proportions across different tissues. This is why a single hormone can do so many different things in different places. The reproductive system is the obvious territory: estrogen thickens the uterine lining, supports follicle development, and shapes cervical mucus into its fertile, glassy form around ovulation. But the reach extends much further.
In the bones, estrogen maintains density by slowing the cells that break bone down. This is why bone density falls so quickly after menopause, and why the risk of osteoporosis rises with it.
In the brain, estrogen influences serotonin and dopamine — the two molecules most associated with mood and motivation. When estrogen is high, serotonin tends to be more available. When she falls, mood often falls with her. This is one of the reasons mood shifts across the cycle, and part of the mechanism behind PMS and PMDD.
In the cardiovascular system, estrogen supports vascular flexibility and helps keep cholesterol patterns favourable. The relative protection against heart disease that premenopausal women have, compared to men of the same age, is in part hers.
In the skin, she supports collagen production and hydration. In the gut, she influences motility. In the breasts, she supports tissue development. In the body's metabolism, she affects insulin sensitivity and fat distribution. She influences sleep, verbal memory, the immune system, the moisture of mucous membranes, the shape of the voice.
The list is long, and incomplete.
Estrogen is not a reproductive hormone. She is a whole-body hormone that happens to also do reproduction.
How she moves through the cycle
Inside a single cycle, estrogen has two peaks.
The first comes in the late follicular phase, just before ovulation. As a dominant follicle matures, the granulosa cells around it produce more and more estradiol, climbing steeply day by day. When the level crosses a particular threshold, the brain switches its response. What had been a calming feedback signal — enough hormone, settle down — becomes a triggering one, and the pituitary releases a sudden burst of luteinizing hormone. This is the LH surge, and it is what causes ovulation. Estrogen, in other words, is what tells the body when to release the egg.
After ovulation, estradiol drops briefly, then rises again as the corpus luteum — the structure left behind by the released follicle — produces both estrogen and progesterone together. This second, smaller peak sits in the middle of the luteal phase. If pregnancy does not occur, both hormones fall together near the end of the cycle, and the bleed begins.
Two peaks, then. One bright and outward, the one that brings the Tuesday at the post office. The other quieter, working in tandem with progesterone, more grounded.
The conversations she keeps
Estrogen rarely acts alone. Most of what she does is in dialogue with another hormone.
With FSH and LH, the two messengers from the pituitary, she negotiates the cycle itself. At low levels, she dampens their release. At her pre-ovulatory peak, she flips that switch and triggers the LH surge that releases the egg. The cycle is, in a sense, this back-and-forth.
With progesterone, she dances. Estrogen builds the uterine lining; progesterone matures and stabilizes it. Estrogen tends to lift mood and energy; progesterone tends to calm. They are partners more than opposites, and the balance between them often matters more than the absolute level of either.
With testosterone, she shares a precursor. Aromatase — the same enzyme that turns androgens into estrogens in fat tissue — links these two hormones directly. This is why hormonal balance is rarely a question of one molecule alone.
With serotonin and dopamine, she sets the tone. The mood shifts across the cycle are, in large part, this conversation — estrogen rising and serotonin's availability rising with her, estrogen falling and the floor going with it.
With cortisol, the stress hormone, the conversation is harder to hear but always there. Chronic stress appears to thin the body's production of sex hormones over time, possibly by competing for the same precursor molecules. Whether the precise mechanism is what older texts called pregnenolone steal is debated, but the observation — that prolonged stress disrupts the cycle's hormones — is consistent across the literature.
With the gut microbiome, of all places, she also has a relationship. A subset of gut bacteria, collectively called the estrobolome, produces enzymes that can reactivate estrogens the liver has marked for excretion, recirculating them back into the body. A balanced gut microbiome supports balanced estrogen levels. An unbalanced one can quietly tip them in either direction.
Across a life
Estrogen is not constant. She rises in puberty. She holds court for thirty-some years of cycling. She climbs to extraordinary levels during pregnancy. And then, in perimenopause, she begins to fluctuate before settling, eventually, much lower. The settling is what we call menopause — not an absence of estrogen, but a quieter, mostly estrone-led version of her.
Each of these chapters has its own weather, and each deserves its own letter. We will write them.
A quiet close
Estrogen is the hormone most often blamed and least often understood. She does not make you irrational. She does not make you difficult. She is a whole-body messenger doing real work in your bones and your brain and your blood vessels and your skin, every day, and her presence is most of what people are pointing at when they say hormonal.
To know her is to begin hearing the rest of the cycle differently.
Freyja's tracking is here when you are ready to begin watching her rise and fall in your own body. There is no better introduction than two cycles of paying attention.
Download the Freyja app to track and further understand your body.
Download from Apple App Store or Google Play Store