Introduction

More than one third of the women in the United States, about 36 million, have been through menopause. With a life expectancy of about 81 years, a 50-year-old woman can expect to live more than one third of her life after menopause. Scientific research is just beginning to address some of the unanswered questions about these years and about the poorly understood biology of menopause.

Menopause is the point in a woman's life when menstruation stops permanently, signifying the end of her ability to have children. Known as the "change of life," menopause is the last stage of a gradual biological process in which the ovaries reduce their production of female sex hormones - a process which begins about 3 to 5 years before the final menstrual period. This transitional phase is called the climacteric, or perimenopause.

Menopause is considered complete when a woman has been without periods for 1 year. On average, this occurs at about age 50. But like the beginning of menstruation in adolescence, timing varies from person to person. Cigarette smokers tend to reach menopause earlier than nonsmokers.

How Does It Happen?

The ovaries contain structures called follicles that hold the egg cells. You are born with about 2 million egg cells and by puberty there are about 300,000 left. Only about 400 to 500 ever mature fully to be released during the menstrual cycle.

The rest degenerate over the years. 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. The follicle also increases production of the sex hormones estrogen and progesterone, which thicken the lining of the uterus. This enriched lining is prepared to receive and nourish a fertilized egg following conception. If fertilization does not occur, estrogen and progesterone levels drop, the lining of the uterus breaks down, and menstruation occurs.

For unknown reasons, the ovaries begin to decline in hormone production during the mid-thirties. In the late forties, the process accelerates and hormones fluctuate more, causing irregular menstrual cycles and unpredictable episodes of heavy bleeding. By the early to mid-fifties, periods finally end altogether.

However, estrogen production does not completely stop. The ovaries decrease their output significantly, but still may produce a small amount. Also, another form of estrogen is produced in fat tissue with help from the adrenal glands (near the kidney). Although this form of estrogen is weaker than that produced by the ovaries, it increases with age and with the amount of fat tissue.

Progesterone, the other female hormone, works during the second half of the menstrual cycle to create a lining in the uterus as a viable home for an egg, and to shed the lining if the egg is not fertilized. If you skip a period, your body may not be making enough progesterone to break down the uterine lining. However, your estrogen levels may remain high even though you are not menstruating.

At menopause, hormone levels don't always decline uniformly. They alternately rise and fall again. Changing ovarian hormone levels affect the other glands in the body, which together make up the endocrine system. The endocrine system controls growth, metabolism and reproduction. This system must constantly readjust itself to work effectively. Ovarian hormones also affect all other tissues, including the breasts, vagina, bones, blood vessels, gastrointestinal tract, urinary tract, and skin.

Surgical Menopause

Premenopausal women who have both their ovaries removed surgically experience an abrupt menopause. They may be hit harder by menopausal symptoms than are those who experience it naturally. Their hot flashes may be more severe, more frequent, and last longer. They may have a greater risk of heart disease and osteoporosis, and may be more likely to become depressed. The reasons for this are unknown. When only one ovary is removed, menopause usually occurs naturally. When the uterus is removed (hysterectomy) and the ovaries remain, menstrual periods stop but other menopausal symptoms (if any) usually occur at the same age that they would naturally. However, some women who have a hysterectomy may experience menopausal symptoms at a younger age.