Hot Flashes - The Symptoms Of Menopause: Menopause Managing The Change Of Life

Content provided by the Faculty of the Harvard Medical School

Hot flashes

Also called vasomotor symptoms, hot flashes may begin in perimenopause, or they may not start until after the last menstrual period has occurred. On average, they last three to five years and are usually worse during the year following the last menstrual period. For some women they go on indefinitely.

Hot flashes probably begin in the hypothalamus, a part of the brain that controls body temperature (see "What is a hot flash?" below). For reasons that remain elusive, the thermostat in a midlife woman's body is suddenly reset at a temperature lower than normal. The hot flash is the body's way of cooling itself, like the way a refrigerator kicks on when you open the door on a hot day.

What is a hot flash? Women have endured the discomfort and embarrassment of hot flashes for centuries. Yet it wasn't until 1975 that this hallmark of menopause came under scientific scrutiny. A study that year in the Journal of Applied Physiology documented physiological changes that occurred during hot flashes — skin temperatures rose and fell, sweating occurred, and the heart rate increased by 13% at the beginning of a flash. The 1975 study finally put to rest the notion that hot flashes were more imagined than real. A variety of studies have shown that the prevalence of hot flashes varies greatly among different cultures. The phenomenon has been studied most often in white women in Western cultures. But additional studies have examined hot flashes among women in Japanese, Filipino, Indian, Mayan, and Native American cultures, to name a few. While up to 80% of American women have hot flashes, Japanese women have a much lower prevalence. In Mexico's Yucatan peninsula, Mayan women do not report hot flashes. Researchers have speculated as to whether these variations are the result of differences in diet, exercise, perceptions of hot flashes, or other cultural factors. However, answers remain elusive. The biggest mystery about hot flashes is the physiological mechanism that causes them in the first place. It's commonly accepted that hot flashes are associated with decreasing estrogen, but there's more to it than that. Before puberty, girls have low estrogen but no hot flashes. Conversely, women in the late stages of pregnancy may have hot flashes at a time when their estrogen levels are high. Hot flashes also have been reported in premenopausal women treated with a drug that affects levels of follicle-stimulating hormone and luteinizing hormone, which control the menstrual cycle, even though their estrogen levels had not greatly decreased. Fluctuating hormone levels may be a key factor. Researchers have examined the complex interactions that occur among more than a dozen hormones and other substances during hot flashes, but as yet they haven't arrived at any clear-cut conclusions about how or if they cause hot flashes. However, the secretion of many of these hormones is regulated in the brain by the hypothalamus, which houses the body's thermoregulatory center. Researchers believe that something happens in this center that causes the body's thermostat to be altered. The result is a hot flash, a feeling of excessive warmth if the body gets just a little overheated. In an attempt to cool itself, the body perspires and blood vessels dilate, causing skin to turn pink or red. After a brief time, maybe a few minutes, the heat dissipates, leading to chills. Source: Adapted from Freedman, RR. Seminars in Reproductive Medicine 2005; 23 (2): 117-125. Research has at least helped explain why some women have hot flashes and others don't. Researchers found that women who have hot flashes have a lower tolerance for small increases in the body's core (innermost) temperature than women who don't have hot flashes. The body tries to maintain its core temperature within a comfortable "thermoneutral zone." When your core temperature rises above the zone's upper threshold, you sweat; when it drops below the lower threshold, you shiver. Women who don't have hot flashes have a thermoneutral zone of several tenths of a degree centigrade. But in women with hot flashes, this thermoneutral zone is extremely narrow (see illustration). As a result, small variations in core body temperature that don't trouble some women trigger hot flashes (and chills) in others. What causes the thermoneutral zone to narrow? One idea is that elevated levels of the brain chemical norepinephrine are involved. Norepinephrine has been shown to reduce the thermoneutral zone in animals. The fact that the drug clonidine, which lowers norepinephrine, widens the zone in women with hot flashes supports this notion. This is true for estrogen and certain antidepressants as well, although scientists still don't understand all the mechanisms.

Hot flashes can be extremely troubling for the 15% of women who have the most severe form. Women who have had surgical menopause or those who are taking tamoxifen to prevent breast cancer are often in this unfortunate group.

The outward signs of a hot flash — sweating and pink or reddened skin — tell the world that a woman's estrogen production is dwindling. Heart palpitations and feelings of anxiety, tension, or a sense of dread also may accompany hot flashes; some women say they feel agitated or unsettled right before a hot flash occurs. Women experience hot flashes differently. Some feel warm; others complain of burning up. A lot of women feel chills afterward. Hot flashes that occur during sleep, called night sweats, may disrupt sleep, causing fatigue and mood changes.

Treating hot flashes. Depending on their severity and how much they affect your day-to-day activities, you can take several steps to help alleviate hot flashes. Begin with a commonsense approach. Some possible triggers of hot flashes are hot beverages, spicy food, warm air temperatures, stressful situations, alcohol, caffeine, and some medications. If you can identify your own triggers, you may be able to avoid some hot flashes. Keep a diary to note which of these or other triggers were present before each hot flash. Review it each week to pinpoint the most common triggers.

During the day, dress in layers so that you can take off garments when needed. If possible, regulate the air conditioning and heat in your environment to accommodate your temperature changes. If you wake up hot at night, sleep in a cool room. Go to bed with a frozen cold pack under your pillow, and turn the pillow over when you wake up. Keep a change of nightclothes next to your bed so that you can change easily if you wake up soaked.

Some women find deep-breathing exercises helpful. Research suggests that a technique called paced respiration can cut in half the frequency of hot flashes. To perform paced respiration, take slow, deep, full breaths — expanding and contracting the abdomen gently while inhaling and exhaling — at a rate of about six to eight breaths per minute. One of the best ways to learn paced respiration is by taking a yoga class. Practice this technique twice a day for 15 minutes. You can also use paced respiration whenever you feel a hot flash coming on. Stress-relief techniques and biofeedback may also be of some benefit.

Increasing the soy in your diet has been shown to be helpful in some but not all studies. Over-the-counter remedies that some women find helpful include preparations of black cohosh, sold under the brand name Remifemin. There are many other products containing plant estrogens (phytoestrogens), but many have not been scientifically evaluated for either safety or efficacy. Some women report that vitamin E is helpful, but compelling evidence to support this is lacking.

It is important to remember that all of the hot flash studies using a placebo show that at least 25%–30% of women respond to the placebo. That's worth knowing before you spend money on over-the-counter remedies. In addition, most hot flashes wax and wane, although the summer months can be especially difficult.

Short-term hormone therapy is quite effective in treating hot flashes. Doctors now prescribe lower doses than they did previously because of health risks of these medications (see "Estrogen and progestogen regimens"). If you can't or don't want to take hormones, you may find that an antidepressant such as venlafaxine (Effexor) or fluoxetine (Prozac) helps. Certain antihypertensive medications such as clonidine (Catapres) relieve hot flashes in some women. An antiseizure medication, gabapentin (Neurontin), has also shown some promise. Talk with your clinician about which medication may be right for you, and remember that most hot flashes improve over time on their own.

Figure 4: When do symptoms start and stop? Certain symptoms such as irregular periods appear earlier in perimenopause. Others, such as vaginal dryness, start somewhat later but continue through postmenopause. Diseases such as heart disease and cancer tend to appear later in the postmenopausal years. Source: Journal of the Society of Obstetricians and Gynecologists of Canada, 1998: 20:6

E-mail This | Print This Previous Chapter | Next Chapter

Last updated:	August 13, 2007