What Is Estrogen and Why Is It Important?

All hormones act as chemical messengers that travel throughout the body, carrying information and instructions to every cell. Most estrogen is produced in the ovaries, although the adrenal glands and fat tissue also make small amounts.

The main role of estrogen is to bring about puberty in young girls, which happens when estrogen circulating in the blood binds with receptors in targeted areas. The result is the start of menstruation and the growth of breasts and pubic hair. Although this is the primary role of the hormone, estrogen affects many other parts of the body as well.

Excess estrogen levels can occur due to hormone replacement therapy, stress, or regular monthly fluctuations. Signs of elevated estrogen include weight gain, fatigue, depression, anxiety, worsening of PMS, cramping, bleeding, and decreased sex drive. More serious signs include fibrocystic breasts or fibroids in the uterus. Neither of these conditions is malignant, but they may cause significant discomfort. Men with elevated estrogen may experience growth of breast tissue and infertility.

The most common cause of low estrogen is menopause, but it can also come as the result of surgical removal of the ovaries. Symptoms include fewer, shorter menstrual periods, night sweats, hot flashes, decreased sex drive, mood swings, dry skin, and thinning of the vagina. The drop in estrogen can also cause severe headaches. For men, low estrogen can lead to low sex drive and an increase in belly fat.

There are three types of natural estrogen: estradiol, estriol, and estrone. Estradiol or oestradiol is the strongest form of estrogen; it is made in the ovaries and responsible for maturing and maintaining the female reproductive system. This hormone prepares and releases the egg during menstruation and thickens the uterine wall so that a fertilized egg can implant. Because the ovaries are the primary producer of estradiol, production significantly declines when women begin menopause. Interestingly, this is a form of estrogen that men need, although in much smaller amounts, because it also contributes to brain function and bone health.

Estriol is a form of estrogen that is dominant only during pregnancy. It is primarily secreted by the placenta and is the weakest type. In women who are not pregnant but have not yet reached menopause, estriol is typically only a byproduct of the liver breaking down other forms of estrogen also produced in the ovaries. Experts believe that estriol affects blood flow and vascularization of the placenta. For this reason, it is often measured during prenatal testing and used as a marker for possible fetal abnormalities.

The third form of estrogen is estrone. It is produced by the ovaries, fat tissue, and adrenal glands. This is the weakest form and is more prominent in post-menopausal women. Sometimes, it can be converted to more potent estrogen when needed.

Menopause is the biggest reason for fluctuations in estrogen, but it is not the only reason. Birth control pills, pregnancy, and replacement therapies can also cause estrogen levels to change. Levels also vary throughout the menstrual cycle, peaking during fertile days and dropping to their lowest during a period. The body stops preparing for pregnancy, so hormones drop and the uterine lining is shed so that the cycle can start over again.

Estrogen is also important for bone health, working in conjunction with vitamin D and calcium. Lower estrogen levels in postmenopausal women is a major contributor to the prevalence of osteoporosis in this demographic. Bone growth slows around age 30 and, after menopause, the body begins to break down more bone than it replaces. Although this bone loss eventually levels off, the decrease in estrogen continues to affect bone strength. After menopause, it is not uncommon for a woman to lose as much as 20 percent of her bone mass.

There are several forms of estrogen replacement therapy, including systemic estrogen in the form of a patch, cream, gel, spray, or pill, and combined estrogen and progesterone therapy. Low dose estrogen treatment is also an option. Hormone therapy has risks, and some are quite significant. Certain options increase the risk of heart disease, blood clots, breast cancer, and stroke, though the risk varies depending on the age at which a woman begins the therapy. On the other hand, estrogen replacement is an effective therapy for women going through menopause and can help decrease the risk of anxiety, depression, and osteoporosis, among other things. Current age, age of menopause onset, and general health all contribute to whether hormone replacement therapy is a good option.