You know what menopause feels like — but do you know why it happens? Understanding what's going on in your body could help you better manage your symptoms.
The signs of menopause are obvious: Your periods end, you start having hot flashes that can leave you red-faced and perspiring, and a host of other unwelcome menopausal symptoms become a part of your day-to-day life.
But what leads to these changes in a woman's body? The short answer is, decreasing levels of the hormones that regulate monthly menstruation cycles, mainly estrogen and progesterone.
The Normal Menstrual Cycle
A number of key hormones regulate the normal menstrual cycle. It begins with one called follicle-stimulating hormone (FSH), which is produced in the pituitary gland in the brain. FSH prompts the ovaries to develop several follicles, or sacs, each of which contains an egg. Later, when FSH levels fall, only one follicle, called the dominant follicle, continues to grow. It then produces the hormone estrogen, which helps build the lining of the uterus to prepare for a possible pregnancy.
When estrogen reaches a certain level, another pituitary hormone, luteinizing hormone (LH), surges, stimulating the ovary to release the egg. This is known as ovulation. The ovary then begins to produce the hormone progesterone, which, together with estrogen, makes the lining of the uterus thicken even more and fill with nutrients to nourish a fertilized egg. If there is no pregnancy, progesterone and estrogen levels drop, the uterine lining is shed through menstruation, and the cycle starts again.
When Hormones Go Haywire
"In perimenopause — the months or years of menopausal symptoms leading up to menopause — the finely tuned repetitive process of menstruation goes awry," says Marcie Richardson, MD, director of the Harvard Vanguard Menopause Consultation Service and the editor of Flashes, the North American Menopause Association's monthly newsletter. In fact, although the average age of menopause in the United States is 51, the ovaries naturally begin to slow their production of estrogen and progesterone as early as a woman's late thirties. This is because the number of follicles in the ovaries begins to decline steeply around this time. As a result, the ovaries make less of the hormones needed to help those follicles mature.
Fewer follicles also means that some women ovulate less often, and when they don't ovulate, they don't make progesterone. This leaves estrogen unopposed, leading to an erratic buildup of the lining of the uterus and causing irregular menstrual bleeding — periods that are heavier or lighter than normal as well as longer or shorter.
As a woman gets closer to menopause, estrogen levels also drop. Because estrogen affects many parts of the body, including the brain, breasts, heart and blood vessels, uterus, urinary tract, and skin, its decline is thought to cause many of the more undesirable symptoms of menopause, such as hot flashes and vaginal dryness. During perimenopause, varying levels of estrogen can trigger unwelcome symptoms too. "You can also have estrogen spikes, when estrogen goes above the level that's normally seen in the menstrual cycle, and that can be responsible for breast tenderness or fibroid growth," says Dr. Richardson.
By the time of menopause, only a few hundred to a few thousand of the 1 to 2 million eggs a female is born with may remain. The ovaries stop releasing eggs, and they produce much less estrogen and no progesterone. Because the levels of these two hormones are now so low, the lining of the uterus no longer builds up and menstruation stops. Experts agree that 12 months after a woman's last menstrual period, she has officially reached menopause.
Richardson points out that although every woman eventually reaches menopause, the timing and process is unpredictable. "Some women just suddenly stop having periods, but others go through years of hormonal ups and downs before their periods finally stop," she says. "Every woman has her own script."
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