Estrogen

Estrogen is a class of hormones that plays an important role in female reproductive and sexual development. The estrogen class includes three specific hormones with related functions: estradiol, estriol, and estrone. Females produce these substances in varying amounts throughout their lives, with average levels of some estrogen hormones rising during reproductive age and others being more prevalent after menopause. Puberty and pregnancy also affect average production levels of particular estrogen hormones. Although estrogen is considered a class of female sex hormones, males produce small amounts of estrogen, and studies have shown that it plays a relatively limited but significant set of functions in their overall health. The main purpose of estrogen hormones is to regulate the growth, maintenance, and repair of the elements of the female reproductive system. It also helps to develop the female secondary sex characteristics and aids in other sexual and reproductive functions. The estrogen hormone estradiol plays a key role in bone health.

Background

Hormones are chemicals that are produced by the human body. They are commonly described as "chemical messengers," meaning that their production and presence in specific quantities triggers a natural reaction or tells the body to do something specific. For example, production of the hormone melatonin rises after nightfall, signaling to the body that the time to go to sleep is approaching. Melatonin plays a major role in regulating the sleep-waking cycle. Its presence prompts a series of physiological and psychological responses, including drowsiness. During daylight hours, melatonin levels decline, and the responses it triggers recede.

Some hormones are found in roughly equal quantities in males and females, while others are usually found in far greater amounts in one sex or the other. Although males naturally produce estrogen in small quantities, it is strongly associated with the female body due to its origins in the ovaries and role in the female aspects of reproduction and sexuality. The male equivalent of estrogen is androgen. Androgen hormones are mainly produced in the testicles. Like estrogen in females, average androgen levels are much higher in males than in females. Like estrogen in males, females also naturally produce small quantities of androgen hormones, and they play a limited but significant role in female health.

Under normal circumstances, the body releases estrogen hormones in short pulses, and the amount of estrogen active in the body at any given time differs from hour to hour throughout the day. In both males and females, abnormally high or abnormally low estrogen levels can cause symptoms and medical conditions. Treatments known as hormone management or hormone replacement therapy may be necessary to bring symptoms and conditions under control.

Overview

Estradiol is the major estrogen hormone found in females of reproductive age. Its production and secretion begins when ovarian follicles develop and become active, a process that usually accelerates with the onset of puberty. In females, estradiol is responsible for breast development and maintenance, and other physiological changes that occur during puberty and postpubescence, including expansion of the hips, curvature of the lower back, and fat distribution patterns that give the buttocks a rounded profile. These features are known as secondary sex characteristics, meaning that they are not present at birth. In addition, estradiol governs the growth and development of the cervix, endometrium, fallopian tubes, and vagina. It also regulates the ovulation cycle and strengthens the myometrium, which is the layer of muscles found in the womb.

Beyond these primary functions, estradiol assists the growth and maintenance of bones and joints. Declining estradiol levels are one of the main reasons women are at elevated risk for osteoporosis after menopause. The brain also produces small amounts of estradiol, and researchers believe that it helps protect neurological function.

Estriol is primarily secreted as a by-product of estradiol, and for much time, doctors and researchers widely considered its role and importance inconsequential. However, studies suggest that estriol can help ease some of the symptoms associated with menopause, such as vaginal dryness, bone density reduction, and hot flashes. Because it is active in the placenta, estriol levels tend to rise sharply during pregnancy. In nonpregnant females, estriol levels can be so low that they are functionally undetectable.

Estrone is the main estrogen hormone produced by menopausal women. It is thought to signal a decline in reproductive function and is a known contributor to the development of breast cancer. Females with unusually high estrone levels are considered to be at elevated risk for developing breast cancer.

In addition to their physiological functions, estrogen hormones also have psychological and emotional effects. They are thought to play a major role in the mood disturbances that can accompany the premenstrual period in females, and they are also believed to boost the brain's production of serotonin and endorphins. However, researchers have yet to definitively identify estrogen's exact mechanisms of action with regard to mood and emotions.

Unusually low or high estrogen levels can produce symptoms in both sexes. In females, low estrogen levels are associated with diminished sex drive, dry skin, hot flashes, insomnia, interruptions in the menstrual cycle, mood swings, and vaginal dryness. Men with unusually low estrogen levels may report diminished sex drive and accumulation of fat in the stomach area. Low levels may also contribute to the development of osteoporosis in older males. Females with abnormally high estrogen levels can experience anxiety, depression, fatigue, weight gain, unusually light or heavy menstrual bleeding, and the development of noncancerous growths in the breasts and/or uterus. In males, elevated estrogen levels are associated with a condition known as gynecomastia, or male breast development, impotence, and infertility.

Beyond its natural production in the human body, estrogen hormones can be manufactured. Synthetic estrogen is used in hormone management and hormone replacement therapy, which may be offered to members of either sex who have unusually low estrogen levels. Male-to-female transgender individuals may elect to undergo hormone therapy to develop some of the physical characteristics associated with women. Manufactured estrogen is a key component of birth control pills, which are essentially designed to trick the body into thinking it is pregnant to induce the temporary cessation of ovulation.

Estrogen also is linked to certain diseases, including cancer (mainly breast cancer) and endometriosis, a medical condition in which bodily tissues that normally grow on the inside of the uterus and ovaries instead grow on the outside. Endometriosis can be treated by artificially reducing estrogen levels in the body, but this carries risks and potential side effects, including decline in fertility and reproductive function.

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