Estrogens are a group of sex hormones that promote the development and maintenance of female characteristics in the human body.
They play an essential role in the growth and development of female secondary sexual characteristics, such as breasts, pubic and armpit hair, and the regulation of the menstrual cycle and reproductive system.
During the menstrual cycle, estrogen produces an environment suitable for the fertilization, implantation, and nutrition of an early embryo.
An imbalance of these hormones can lead to a range of health problems and unwanted physical changes. This MNT Knowledge Center article will explain what estrogen is, how it works in the body, its range of medical uses, and the effects of estrogen imbalance.
Fast facts on estrogen
- The ovaries are the main location for estrogen production.
- Estrogen influences the structural differences between the male and female bodies, such as females having a wider pelvis and more permanent hair on the head.
- Synthetic estrogen has a range of uses in medicine, including birth control and managing the effects of menopause.
- Estrogen is involved in the development of a range of health issues.
Hormones are chemical messengers that tell specific tissues to behave in a certain way.
During puberty, the ovaries begin releasing estrogen hormones in line with each monthly menstrual cycle. The estrogen level rises suddenly halfway through the cycle, which triggers the release of an egg. This level then quickly decreases after ovulation.
Estrogens usually travel through the bloodstream in fluids, interact with cells in a variety of tissues in the body, and deliver a message or instruction.
It is one of the most important hormones for women, alongside progesterone. Progesterone helps to maintain pregnancies and implant an egg in the uterus.
The related hormones in the estrogen family include:
- Estrone (E1): This is a weak form of estrogen and the only type found in women after the menopause. Small amounts of estrone are present in most tissues of the body, mainly fat and muscle. The body can convert estrone to estradiol and estradiol to estrone.
- Estradiol (E2): This is the strongest type of estrogen. Estradiol is a steroid produced by the ovaries. It is thought to contribute to a range of gynecological problems, such as endometriosis, fibroids, and cancers that occur in females, particularly endometrial cancer.
- Estriol (E3): This the weakest of the estrogens and is a waste product made after the body uses estradiol. Pregnancy is the only time at which significant amounts of estriol are made. Estriol cannot be converted to estradiol or estrone.
Far lower levels of estrogen are also present in men.
Estrogen is crucial to the reproductive function and cycle of a woman.
In females, estrogen affects the following areas of the body:
- Ovaries: Estrogen helps stimulate the growth of an egg follicle.
- Vagina: It also stimulates the growth of the vagina to its adult size, the thickening of the vaginal wall, and an increase in vaginal acidity that reduces bacterial infections. It also helps lubricate the vagina.
- Fallopian tubes: Estrogen is responsible for the growth of a thick, muscular wall in the fallopian tubes, and for the contractions that transport the egg and sperm cells.
- Uterus: Estrogen enhances and maintains the mucous membrane that lines the uterus. It increases the size of the endometrium as well as enhancing blood flow, protein content, and enzyme activity. Estrogen also stimulates the muscles in the uterus to develop and contract. Contractions help during the delivery of an infant and placenta, and they also assist the wall of the uterus in getting rid of dead tissue during menstruation.
- Cervix: Estrogen is thought to regulate the flow and thickness of uterine mucous secretions. This enhances the movement of a sperm cell to an egg and enables fertilization.
- Mammary glands: Estrogen forms unique relationships with other hormones in the breast. They are responsible for the growth of the breasts during adolescence, the pigmentation of the nipples, and eventually stopping the flow of milk when an infant is no longer breast-feeding.
Estrogen is responsible for the differences between male and female bodies. For example, in a female body:
- Estrogen makes the bones smaller and shorter, the pelvis broader, and the shoulders narrower.
- It increases fat storage around the hips and thighs, meaning that the body is more curved and contoured.
- Estrogen helps to slow down the growth of females during puberty and increases sensitivity to insulin. Insulin influences the amount of body fat and lean muscle a person can develop.
- It influences body hair to become finer and less pronounced while making the hair on a woman's head more permanent.
- Estrogen makes the voice box smaller and the vocal cords shorter, giving females a higher-pitched voice than males.
- Estrogens suppress the activity of the glands in the skin that produce oily substances. This reduces the likelihood of acne in females.
Other areas on which estrogen has an impact include:
- The brain: It can help maintain body temperature, regulate the part of the brain linked to sexual development, and enhance the effects of the brain's "feel-good" chemicals.
- The skin: Estrogens improve the thickness and quality of the skin as well as the collagen content which prevents aging.
- The bones: Estrogen helps to preserve bone strength and prevent bone loss.
- The liver and heart: The hormone regulates cholesterol production in the liver, helping to protect the heart and arteries.
Some foods contain phytoestrogens, which may affect levels of estrogen in the body.
- cruciferous vegetables
- soy and some foods containing soy protein, the most concentrated source
- seeds and grains
Some scientists consider phytoestrogens to be endocrine disruptors. They appear to have dual functions at times, able to increase and decrease estrogen activity.
It is a common misconception that phytoestrogens can negatively impact health, but some research confirms that the foods containing phytoestrogens listed above can lower cancer risk, reduce hot flashes, improve other menopausal symptoms, and provide other health benefits.
The effects of soy's phytoestrogens depend on the type of soy being studied at the time, and this has led to inconsistent findings. Soy protein isolate will have a different impact from whole soy foods.
Synthetic estrogen, bio-identical estrogen, and estrogens derived from pregnant mares (Premarin) are used for a range of medical purposes.
The most common uses of estrogen are in birth control pills and hormone replacement therapy (HRT) and bio-identical hormone replacement therapy (BHRT) for menopause.
Birth control pill
The birth control pill is the most commonly used method of birth control in the United States. Estrogen is included in combination oral birth control pills alongside the hormone progestin.
Many women take low-dose birth control pills, which contain 20 to 50 micrograms (mcg) of estrogen.
The estrogen in the combined pill sends feedback to the brain. This feedback causes a range of effects in the body, including:
- stopping the pituitary gland from secreting follicle-stimulating hormone (FSH)
- stopping the production of luteinizing hormone (LH)
- preventing ovulation
- supporting the lining of the womb to prevent the breakthrough bleeding that can sometimes cause spotting between periods
Some doctors may prescribe birth control for alternative uses, including:
- regulating the menstrual cycle
- easing severe cramping and heavy bleeding
- reducing the risk of ovarian cancer and the development of ovarian cysts
- protecting against ectopic pregnancy
- decreasing perimenopausal symptoms
- helping reduce the severity of hormone-related acne
Taking a birth control pill carries a range of risks, such as:
- heart attack
- blood clots
- pulmonary embolism
- nausea and vomiting
- irregular bleeding
- weight changes
- breast tenderness and swelling
Long-term use may also lead to a higher risk of breast cancer.
Hormone replacement therapy
Hormone replacement therapy (HRT) aims to relieve some symptoms of menopause by bringing the levels of female hormones back to normal. The treatment can be provided as estrogen-only or as a combination of estrogen and progestin.
For women who still have a uterus, the hormone progestin is used alongside estrogen to prevent the overgrowth of the uterine lining, which can lead to endometrial cancer. HRT is available as a pill, nasal spray, patch, skin gel, injection, vaginal cream, or ring.
HRT may help relieve symptoms of menopause, such as:
- hot flashes
- vaginal dryness
- painful intercourse
- mood swings
- sleep disorders
- decreased sexual desire
The US Food and Drug Administration (FDA) recommends that HRT is used at the lowest doses for the shortest duration needed to achieve treatment goals.
This can help to avoid some of the uncomfortable side effects, such as:
- breast soreness
- mood swings
- water retention
Women who use or are considering using hormone therapy after menopause should discuss the possible benefits and health risks with their physicians.
Hormone therapy is also used to help transgender people who wish to transition between genders, with estrogen often being prescribed to help transgender women who are looking to develop female secondary sexual characteristics.
Due to the risks posed by this type of therapy, it is vital that a course of hormone therapy is followed under supervision by a medical professional.
Estrogen replacement therapy (ERT)
Estrogen replacement therapy (ERT) is used to increase estrogen levels in women who have undergone menopause and have had their uterus removed. This is because ERT is linked to uterine cancer but would not have this effect in women after removal of the uterus.
ERT can also treat a range of other conditions, such as delayed puberty, symptomatic vaginal atrophy, and breast atrophy.
This treatment may have additional benefits, including:
- preventing symptoms during the menopause
- preventing osteoporosis
- preventing colon cancer
- reducing early bone loss and osteoporosis in women who had their ovaries removed between the ages of 20 and 40 years
ERT can reverse the effects of low estrogen levels and may also:
- control the occurrence and severity of hot flashes
- improve mood and sleep problems that occur due to hormonal changes
- maintain the lining and lubrication of the vagina
- maintain skin collagen levels
- prevent osteoporosis following the menopause
- reduce the risk of dental problems, including tooth loss and gum disease
ERT should be avoided if the person taking them:
- is pregnant
- has unexplained vaginal bleeding
- has liver disease or chronically impaired liver function
- has a strong family history of cancer in the breast, ovaries cancer, or endometrium
- is a smoker
- has a history of blood clots
- has had a stroke
Topical estriol application for vaginal atrophy has been shown to be effective with the least side effects compared to combination estrogen therapy.
Normal estrogen levels can vary a great deal. Differences can typically be seen between the estrogen levels of two women on the same day of their cycles, for example, or in the same woman on different days.
However, when levels fall or rise too far, bodily functions can become irregular.
Certain conditions, lifestyle choices, and processes can reduce the amount of estrogen in the body. These include:
- ovarian failure
- an underactive pituitary gland
- pregnancy failure
- the menopause and perimenopause
- polycystic ovarian syndrome (PCOS)
- anorexia nervosa
- strenuous exercise or training
- certain medications, such as clomiphene
Other factors can lead to a spike in estrogen, such as:
Natural alternatives and supplements, such as black cohosh, are often touted as a treatment for the symptoms of menopause. Research findings have been inconsistent, but side effects from taking black cohosh are reported to be minor and infrequent.
For estrogen-containing supplements, The American Congress of Obstetricians and Gynecologists (ACOG) advises caution. Estrogen is linked to a number of cancers and health risks, and so it is vital to consult with a doctor before taking any supplements. In addition, the FDA cannot regulate or ensure the safety and effectiveness of herbal and non-medicinal supplements.
As estrogen is linked to a number of cancers and health risks, it is vital to consult with a doctor before taking any supplements.
The effects of imbalanced estrogen levels can include the following:
- menstruation becoming less frequent or stopping
- light or heavy bleeding during menstruation
- hot flashes, night sweats, or both
- non-cancerous lumps in the breast and uterus
- mood swings and sleeping problems
- weight gain, mainly in the hips, thighs, and waist
- low sexual desire
- mood swings
- feelings of depression and anxiety
- dry skin
It is important when taking medications that contain estrogen to keep track of symptoms and ensure that you are maintaining balanced estrogen levels.
If you experience any of the above symptoms, speak to your doctor.