You probably know estrogen by its traditional sex-ed definition: A female reproductive hormone. But, like women themselves, estrogen is so much more. In fact, some experts tout estrogen as the most important hormone in the human body no matter your sex. Although it’s true that the ovaries are responsible for a large percentage of estrogen production in women during childbearing years, everyone produces the hormone throughout their lives via their adrenal glands and fat cells.
“You can call estrogen the mother of all hormones and not even be joking,” says Mitchell Creinin, MD, a professor in the department of obstetrics and gynecology at University of California Davis Health. “It was the first hormone that developed in evolution; every organ in the body has a receptor for estrogen.”
Reproduction aside, estrogen plays an important role in numerous functions of the human body while receiving very little credit.
“Estrogen helps the brain function,” says Subbulaxmi Trikudanathan, MD, a spokesperson for the Endocrine Society. “It’s also very important for bone health and skin health, for sexual desire and libido, and it’s responsible for how different cholesterols are metabolized.”
As crucial as it is, most of us know little about estrogen. But that’s about to change. Here’s everything you need to know about the mother of all hormones.
There Are Four Types of Natural Estrogens
For starters, the estrogen produced in the body isn’t a single hormone but rather a collective of four, each with its own characteristics.
Estrone (E1) is produced by the ovaries, adrenal glands and fat cells and is one of two types of estrogens present in men. While E1 is found in women during reproductive years, it really becomes the star in menopause after estradiol levels drop (see more on this next).
Estradiol (E2) is the most potent form of estrogen and the predominant type of estrogen in your body during reproductive years. “It helps to bring about the physical changes that happen in girls during puberty, such as breast development, pubic hair growth and getting the menstrual cycle started,” Dr. Trikudanathan says.” In combination with another sex hormone, progesterone, estradiol continues to be important in regulating your cycle, thickening the uterine lining, and maturing eggs for ovulation each month.
Estriol (E3) is only present in detectable amounts during pregnancy, when it’s produced by the placenta. Its role is to help the uterus expand and prepare the body for childbirth and breastfeeding.
Estetrol (E4) is also found in women during pregnancy, although it’s actually produced by the fetal liver and then travels to the mother via the placenta. E4 was only discovered in 1965 and was largely ignored for the next 35 years. While researchers have yet to pinpoint exactly the role of estetrol in fetal development, it appears to be crucial as the hormone increases steadily until birth and then almost immediately plummets.
The Role of Hormones in Contraception
Estrogen isn’t actually what makes hormonal contraception effective. That’s the job of progestin, a synthetic form of progesterone, which prevents pregnancy primarily by thickening cervical mucus so sperm can’t make it to an egg to fertilize it.
In fact, there are several contraceptives that contain only progestin. Most pills that don’t include estrogen (called “mini-pills”) have really low amounts of progestin and only keep the mucus thick for a little more than 24 hours. If that’s all the progestin your pill contained, you would need to be regimented about taking your birth control at exactly the same time every day for it to be effective.
For the vast majority of us, that’s just flat-out unrealistic. So to prolong the time between doses, birth control manufacturers (thankfully!) increase the amount of progestin in each dose to not only thicken cervical mucus but also prevent the ovary from releasing an egg in the first place. It’s kind of like double the protection, which is why most pills are still effective even if you miss a dose every once in a while. (Reminder: Take the missed pill as soon as you remember to ensure you continue to get protection.)
At this point, you may be wondering: If it’s not necessary for pregnancy prevention, why add estrogen to birth control pills? The answer is that it balances out the increase in progestin. Shutting down your ovaries to prevent ovulation means they aren’t producing as much estrogen. And having additional progestin in your system and a lack of estrogen can make you feel out of balance—which isn’t surprising, given estrogen’s role in the bodily functions discussed earlier.
When women have low estrogen levels because of menopause or for other reasons, they can experience a host of symptoms, says Dr. Trikudanathan. Common ones include:
Menstrual cycles become lighter and infrequent to the point that they don’t occur for a long time or cease altogether.
Hot flushes or night sweats
Thinning of and dryness in the vaginal walls
Difficulty sleeping and insomnia—which could also be caused by the hot flushes
Changes in mood
Is Birth Control That Contains Estrogen Safe?
The good news is that whatever birth control pill you and your doctor decide on, hormonal contraceptives on the market today are highly effective and extremely safe, even when used long-term. Much of that has to do with the amount of hormones now used in birth control pills.
“The content of estrogen in oral contraceptives has reduced a lot,” Dr. Trikudanathan says. Most modern pills contain 10 to 20 micrograms of synthetic estrogen, topping out at 35. Compare that to 50 to 80 micrograms in the pills that were prescribed in the 1960s through 1980s.
That means many of the risks associated with birth control pills of the past are much lower today. Contrary to what you may have heard, large-scale epidemiological research has indicated no significant increase in lifetime cancer risk for healthy women who take the pill. (That being said, Dr. Trikudanathan advises that women with a history of estrogen-receptor-positive breast cancer should not take birth control pills that contain estrogen). In fact, the birth control pill has been shown to reduce your risk of ovarian, endometrial and colorectal cancers, according to the Mayo Clinic.
In the past, higher-dose pills were also associated with blood clots. But that risk, too, has been reduced significantly with the introduction of low-dose pills. “All the pills that we have today are really, really safe,” Dr. Creinin agrees. “Even when it comes to blood clots, the overall risk from currently available birth control is low—much lower than what we see in pregnancy and in the immediate post-pregnancy time frame.”
The Future of Hormonal Birth Control Pills
Hormonal birth control pills are safer than ever. Still, researchers are continuing to develop even better options for women. The latest advancement is the development of a birth control pill that contains estetrol (E4). It’s equally effective at preventing pregnancy and regulating the menstrual cycle as pills that contain synthetic estrogen, but appears to have an even lower risk of blood clots and other complications as compared with birth control pills containing estradiol.
“Estetrol has a positive effect on the uterus to balance out the effects of the progestin so you get good cycle control,” Dr. Creinin says. “It has positive effects on the bone, positive effects on the brain with no effect on the liver, no effect on the kidney, and importantly, no effect on the breast.” E4 is also being studied for use in hormone therapy for the treatment of symptoms of menopause.
“What we’re trying to do with newer products is find something that can minimize whatever risks still exist for healthy users,” Dr. Creinin says. “I think estetrol is potentially a game changer. It’s almost like a designer drug except that it’s a natural estrogen.”
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