Oestradiol, also known as estradiol, is a steroid hormone and the most potent form of estrogen. It is a primary female sex hormone but is present in both sexes. This hormone is produced in the ovaries in females, the testes in males, and in smaller quantities by the adrenal glands and fat cells. During pregnancy, the placenta also becomes a source of oestradiol. The hormone’s influence extends beyond reproduction, affecting various tissues throughout the body, with levels fluctuating naturally over a person’s life.
The Function of Oestradiol in the Body
In the female body, oestradiol drives physical development and reproductive health. Its levels rise during puberty, stimulating secondary sexual characteristics like breast growth, widening of the hips, and changes in fat distribution. Oestradiol also governs the growth and maturation of reproductive organs, including the uterus, vagina, and fallopian tubes.
The menstrual cycle is regulated by fluctuating levels of oestradiol. In the follicular phase, oestradiol from developing ovarian follicles helps mature the egg and thickens the uterine lining (endometrium) for a potential pregnancy. A sharp spike in oestradiol then triggers the release of luteinizing hormone (LH), which causes ovulation.
During pregnancy, oestradiol levels rise substantially, which helps maintain the pregnancy. Beyond reproduction, oestradiol contributes to bone health by regulating bone turnover. It also affects the cardiovascular system by influencing cholesterol and triglyceride metabolism, and impacts the brain, affecting mood and cognitive function.
Oestradiol also has functions in the male body. Produced in the testes and adrenal glands, it helps modulate libido, support erectile function, and aid in sperm maturation. As in females, oestradiol helps maintain bone density in males. It also contributes to brain function and blood vessel health.
Effects of High and Low Oestradiol Levels
Imbalances in oestradiol can lead to various symptoms and medical conditions. The effects depend on whether the levels are too high or too low and differ between sexes. These fluctuations can be a normal part of life stages, like menopause, or indicate an underlying health issue.
Symptoms of High Oestradiol
High oestradiol levels in women can cause numerous symptoms. Persistently high levels are associated with conditions like polycystic ovary syndrome (PCOS), uterine fibroids, and endometriosis. Common signs include:
- Bloating, breast tenderness, and mood swings
- Weight gain, particularly around the hips and thighs
- Changes in menstrual patterns, such as heavier or more frequent periods
- Headaches and fatigue
In men, excess oestradiol disrupts the testosterone-estrogen balance. This can result in gynecomastia (the development of breast tissue), erectile dysfunction, and reduced fertility. Causes for high oestradiol can range from obesity, as fat cells produce estrogen, to certain tumors or liver disease.
Symptoms of Low Oestradiol
A decline in oestradiol is a natural part of menopause, leading to symptoms like hot flashes, night sweats, vaginal dryness, sleep disturbances, and mood changes. Lower oestradiol after menopause also decreases bone density, increasing the risk for osteoporosis. Outside of menopause, low levels can cause irregular or absent periods and may be linked to conditions like primary ovarian insufficiency.
In premenopausal women, low oestradiol can be caused by excessive exercise, low body weight, or issues with the pituitary gland. In men, while their baseline levels are much lower, abnormally low oestradiol can still cause issues. Symptoms may include a decrease in libido, loss of bone density, and an increase in body fat.
Therapeutic Uses of Oestradiol
Synthetic oestradiol is used as a medication to treat conditions caused by a hormone deficiency. A common application is menopausal hormone therapy (MHT), which replaces the oestradiol the ovaries no longer produce. This treatment alleviates menopausal symptoms like hot flashes and vaginal atrophy. MHT is also effective at preventing the bone loss that occurs after menopause, reducing the risk of osteoporosis.
Oestradiol is a component of many hormonal contraceptives, such as birth control pills, patches, and vaginal rings, where it is often combined with a progestin. This combination prevents pregnancy by stopping ovulation. It also works by thickening cervical mucus to make it difficult for sperm to reach the egg and by thinning the uterine lining.
Another application of oestradiol is in gender-affirming hormone therapy for transgender women. This treatment helps induce female secondary sexual characteristics to align physical traits with gender identity. The therapy stimulates breast growth, softens skin, and leads to a redistribution of body fat. Regular monitoring of hormone levels is a standard part of managing the transition effectively.
Measuring Oestradiol Levels
Oestradiol levels are measured with a simple blood test. A healthcare provider may order this test for various reasons, including investigating menstrual irregularities, assessing fertility issues, or diagnosing symptoms of menopause. The test is also used to monitor menopausal hormone therapy or gender-affirming hormone care.
The timing of the blood draw is important for accurate interpretation, as levels fluctuate throughout the menstrual cycle in premenopausal women. A doctor may request the test on a specific day to assess ovarian function. For instance, a test on day three can provide information about ovarian reserve, while a mid-cycle test can help determine if ovulation is occurring.
Factors like age, sex, and pregnancy or menopausal status influence what is considered a normal oestradiol level. Therefore, results must be interpreted within the context of an individual’s overall health and clinical situation. The time of day can also have a minor influence on the readings.