" VIVIAN AIZAWA of Salinas vividly remembers the first time her body was hit by a heat wave out of the blue -- an episode of warmth, flushing and sweating that "almost felt like climate change," the 53-year-old says. The hot flashes and night sweats affected her sleep and strained her relationships. "It is ruining my life," she told her doctor."

" Nearly three out of four women will share Aizawa's experience as they go through menopause. Many, in fact, will get hot flashes and night sweats several times a day for years, each episode lasting from a few seconds to several minutes."

" "It impacts literally millions of women worldwide," says Dr. Wulf Utian, president of the Ohio-based North American Menopause Society, a nonprofit that promotes menopause research. "While not life-threatening, it is a major impediment to their quality of life.""

" For relief, women have tried dozens of remedies: herbs, low-fat diets, antidepressants. Then, in 1942, came a major advance. The U.S. Food and Drug Administration approved Premarin, a form of the female sex hormone estrogen extracted from horse urine. Since then, extensive studies have shown that the hormone, either alone or in combination with other sex hormones, really works: It relieves moderate to severe symptoms in 90% of women who take estrogen."

" But hormone therapy does not suit all women; those with a family history of early breast or ovarian cancer, for instance, probably have to avoid it. And many others have concerns about long-term estrogen use, especially in the years since the landmark Women's Health Initiative trial, which reported a few years back that hormones slightly raised the risk of not only breast cancer but also heart attacks and strokes. (See "Hormones: Is age the key?")"

" Others are willing to take the hormone but suffer unpleasant side effects such as breast tenderness and vaginal discharges. "For these women, the cure is worse than the problem," says Dr. Nananda Col, associate professor of medicine at Brown Medical School in Providence, R.I."

" And so researchers are looking for alternatives -- substances that can calm sweats and flashes while presenting fewer risks. They have identified some possible candidates -- drugs such as the antidepressant venlafaxine, the steroid tibolone and the anticonvulsant gabapentin -- and trials are underway to evaluate some of them. At the same time, scientists are gaining a better understanding of what actually causes hot flashes."

" In hot surroundings, humans cool their bodies in two ways: by sweating, which dissipates heat by evaporation, or by flushing, which cools heated blood by circulating it through dilated blood vessels in the skin."

" In hot-flash sufferers, both responses are often inappropriately triggered by signals from the hypothalamus, the part of the brain that regulates temperature. When this occurs, there is a discrepancy between the woman's sensation of warmth and her actual body temperature."

" Old studies using thermometers placed in the mouth, ear or rectum failed to detect a temperature change during a hot flash. More recent studies, using ingested thermometers, show that there is often a core temperature change, but a small one: less than one-tenth of a degree Fahrenheit. This increase precedes 60% of hot-flash episodes."

" How this tiny thermal spike could trigger such an intense feeling of warmth is less clear, though. Further, small temperature fluctuations occur even in women who don't get hot flashes. Evidently, some women tolerate body temperature fluctuations better than others."

" To explain how this could be, Dr. Robert Freedman, professor of psychiatry at Wayne State University School of Medicine in Detroit, has devised the notion of a "thermoneutral zone," the range of body temperatures a person endures comfortably. It's sandwiched between a "sweating threshold,"
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