What Is It?
Estrogen refers to a group of hormones that play an essential role in the growth and development of female sexual characteristics and the reproductive process.Estrogen is probably the most widely known and discussed of all hormones. The term “estrogen” actually refers to any of a group of chemically similar hormones; estrogenic hormones are sometimes mistakenly referred to as exclusively female hormones when in fact both men and women produce them. However, the role estrogen plays in men is not entirely clear.
To understand the roles estrogens play in women, it is important to understand something about hormones in general. Hormones are vital chemical substances in humans and animals. Often referred to as “chemical messengers,” hormones carry information and instructions from one group of cells to another. In the human body, hormones influence almost every cell, organ and function. They regulate our growth, development, metabolism, tissue function, sexual function, reproduction, the way our bodies use food, the reaction of our bodies to emergencies and even our moods.
The Role of Estrogen in Women
The estrogenic hormones are uniquely responsible for the growth and development of female sexual characteristics and reproduction in both humans and animals. The term “estrogen” includes a group of chemically similar hormones: estrone, estradiol (the most abundant in women of reproductive age) and estriol. Overall, estrogen is produced in the ovaries, adrenal glands and fat tissues. More specifically, the estradiol and estrone forms are produced primarily in the ovaries in premenopausal women, while estriol is produced by the placenta during pregnancy.
In women, estrogen circulates in the bloodstream and binds to estrogen receptors on cells in targeted tissues, affecting not only the breasts and uterus, but also the brain, bone, liver, heart and other tissues.
Estrogen controls growth of the uterine lining during the first part of the menstrual cycle, causes changes in the breasts during adolescence and pregnancy and regulates various other metabolic processes, including bone growth and cholesterol levels.
Estrogen & Pregnancy
During the reproductive years, the pituitary gland in the brain generates hormones that cause a new egg to be released from its follicle each month. As the follicle develops, it produces estrogen, which causes the lining of the uterus to thicken. Progesterone production increases after ovulation in the middle of a woman’s cycle to prepare the lining to receive and nourish a fertilized egg so it can develop into a fetus. If fertilization does not occur, estrogen and progesterone levels drop sharply, the lining of the uterus breaks down and menstruation occurs. If fertilization does occur, estrogen and progesterone work together to prevent additional ovulation during pregnancy.
Estrogen & Perimenopause: The Menopause Transition
Other physical and emotional changes are associated with fluctuating estrogen levels during the transition to menopause, called perimenopause. This phase typically lasts two to eight years. Estrogen levels may continue to fluctuate in the year after menopause. Symptoms include:
•Hot flashes—a sudden sensation of heat in your face, neck and chest that may cause you to sweat profusely, increase your pulse rate and make you feel dizzy or nauseous. A hot flash typically lasts about three to six minutes, although the sensation can last longer and may disrupt sleep when they occur at night.
•Irregular menstrual cycles
•Exacerbation of migraines
•Urinary stress incontinence
Estrogen & Bone Loss
Estrogen produced by the ovaries helps prevent bone loss and works together with calcium, vitamin D and other hormones and minerals to build bones. Osteoporosis occurs when bones become too weak and brittle to support normal activities. Your body constantly builds and remodels bone through a process called resorption and deposition. Up until around age 30, your body makes more new bone than it breaks down. But once estrogen levels start to decline, this process slows. Thus, after menopause your body breaks down more bone than it rebuilds. In the years immediately after menopause, women may lose as much as 20 percent of their bone mass. Although the rate of bone loss eventually levels off after menopause, keeping bone structures strong and healthy to prevent osteoporosis becomes more of a challenge.
Estrogen & Vaginal and Urinary Tract Conditions
When estrogen levels are low, as in menopause, the vagina can become drier and the vaginal walls thinner, making sex painful. Additionally, the lining of the urethra, the tube that brings urine from the bladder to the outside of the body, thins. A small number of women may experience an increase in urinary tract infections (UTIs) that can be improved with the use of vaginal estrogen therapy.
Birth Control Pills
Birth control pills (oral contraceptives) take advantage of this effect by regulating hormone levels. They also result in the production of a very thin uterine lining, called the endometrium, which is unreceptive to a fertilized egg. Plus, they thicken the cervical mucus to prevent sperm from entering the cervix and fertilizing an egg.
Oral contraceptives containing estrogen may also relieve menstrual cramps and some perimenopausal symptoms, and regulate menstrual cycles in women with polycystic ovarian syndrome (PCOS). Furthermore, research indicates that birth control pills may reduce the risk of ovarian, uterine and colorectal cancer.
Estrogen therapy is used to treat certain conditions, such as delayed onset of puberty and menopausal symptoms such as hot flashes and symptomatic vaginal atrophy. Vaginal atrophy is a condition in which low estrogen levels cause a woman’s vagina to narrow, lose flexibility and take longer to lubricate. Female hypogonadism, a condition in which the ovaries produce little or no hormones, as well as premature ovarian failure, can also cause vaginal dryness, breast atrophy and lower sex drive and is also treated with estrogen.
In addition to treating menopause-related symptoms, estrogen and other hormones are prescribed to treat reproductive health and endocrine disorders (the endocrine system is the system in the body that regulates hormone production and function).
Some uses of hormone therapy include the following situations:
•irregular menstrual cycles
Risks of Estrogen Therapy
For many years, estrogen therapy and estrogen-progestin therapy were prescribed to treat menopausal symptoms, to prevent osteoporosis and to improve women’s overall health. However, after publication of results from the Women’s Health Initiative (WHI) in 2002 and March 2004, the U.S. Food and Drug Administration (FDA) now advises health care professionals to prescribe menopausal hormone therapies at the lowest possible dose and for the shortest possible length of time to achieve treatment goals. Treatment is generally reserved for management of menopausal symptoms rather than prevention of chronic disease.
The WHI was a study of 27,347 women aged 50 to 79 (mean age, 63) taking estrogen therapy or estrogen/progestin therapy. They were followed for an average of five and a half to seven years. The study was unable to document that benefits outweighed risks when hormone therapy was used as preventive therapy, and it found that risk due to hormones may differ depending on a woman’s age or years since menopause.
The National Cancer Institute found a very significant drop in the rate of hormone-dependent breast cancers among women, the most common breast cancer, in 2003. In a study published in the New England Journal of Medicine in April 2007, researchers speculated that the drop was directly related to the fact that millions of women stopped taking hormone therapy in 2002 after the results of a major government study found the treatment slightly increased a woman’s risk for breast cancer, heart disease and stroke. The researchers found that the decrease in breast cancer began in mid-2002 and leveled off after 2003. The decrease occurred in women over 50 and was marked in women with tumors that were estrogen receptor (ER) positive—cancers that require estrogen to grow. The researchers speculate that stopping the treatment prevented very tiny ER positive cancers from growing (and in some cases, possibly helped them to regress) because they didn’t have the additional estrogen required to fuel their growth.
However, for symptomatic menopausal women or for women with premature menopause, hormone therapy remains the most effective therapy for hot flashes.