Women in their late 40s and early 50s often complain about mood swings, depression, irritability, fatigue, and lethargy. Some women, and some physicians, write off these symptoms as "just menopause."

That’s a mistake, according to Suzanne Woodward, Ph.D., assistant professor of psychiatry at Wayne State University School of Medicine in Detroit. Sleep disruption triggered by hot flashes may be the true culprit behind such mood upsets.

Appropriate treatment, she said, may considerably improve the quality of life for these women. Woodward spoke at a symposium on the influence of gender on sleep at the annual joint meeting of the American Academy of Sleep Medicine and Sleep Research Society in Las Vegas in June.

Hot flashes are the primary disrupter of sleep in the years just before menopause, she said, affecting three in four women at this time of life. Associated with dramatic fluctuations in hormone secretion, these sudden torrents of warmth that sweep over the face, chest, back, shoulders, and upper arms may prompt heart palpitations and anxiety. While hot flashes vary in frequency from woman to woman, they occur about once an hour on average across the 24-hour day.

In sleep, hot flashes occur mainly in the lighter stages of nondreaming sleep and prompt an arousal from sleep lasting three minutes on average. The cooling that follows a hot flash as body temperature readjusts may involve sweating so profuse that it necessitates a change of nightclothes and sheets, she said, keeping women awake even longer.

Independently of hot flashes, women who have them experience other sleep arousals lasting from a few seconds to about a minute every eight minutes on average. Nonsymptomatic women of the same age, Woodward said, average short-lived sleep arousals every 18 minutes.

It’s important for physicians to recognize that women under-report the hot flashes they experience in sleep, Woodward stressed. The sleep process dulls memory for these awakenings. Few mid-life women, she said, realize how poorly they sleep.

The average age of menopause for women in the United States is 51. The state is defined by a woman’s not having menstruated for a year. Perimenopause—a time of marked decline in ovarian function—starts at age 47.5 on average, usually earlier in women who smoke. This time of life incorrectly is called "being in" or "going through" menopause, Woodward said, suggesting it is more appropriately termed a transition to menopause.

Symptomatology may vary from month to month as hormone levels may oscillate greatly in perimenopause. Hot flashes follow a circadian pattern, she said. The peak in frequency in most women is late evening, when body temperature is near its daily peak. Hot flashes in waking may last from a few seconds to 30 minutes or longer. They typically persist for six months to five years, although some women continue to have them into their 70s. Illnesses such as leukemia also may trigger hot flashes.

Hormone replacement therapy (HRT) can eliminate or reduce hot flashes, and improve both sleep and mood, Woodward said. This treatment also helps keep frequent awakenings from becoming a bad habit that continues after hot flashes subside.

Concerns raised in recent studies about a possible link between HRT and an increased risk of breast cancer, she noted, have made physicians less likely to prescribe this therapy and women more reluctant to take it. The North American Menopause Society estimates that about 15 percent to 20 percent of women approaching menopause have received prescriptions for HRT. The number of those who obtain and use HRT is not known.

Some women turn instead to alternative treatments, such as soy phytoestrogens, acupuncture, and melatonin. Some women report these treatments are helpful, she said, but existing data do not show objective benefits. Most assertions of the efficacy of such treatments rely on self-reports, not sleep studies.

In one of Woodward’s studies, 12 women with hot flashes spent two hours immediately before sleep in a room with hot, cold, or neutral ambient temperature. In the hot environment, they experienced more hot flashes, and in the cool environment, fewer of them. Woodward measured hot flashes objectively with a thermal skin conductance device.

Neither heating nor cooling in the two hours before sleep affected hot flash frequency in sleep when subjects slept in thermoneutral environments. Cooling the sleeping environment, however, did reduce hot flashes, a practical measure women can employ in their own homes.

Woodward advises women who experience hot flashes to keep their home and bedroom cool and to use a fan aimed at their face and upper body while they sleep, even in winter.

Margaret Mead, Woodward noted, said "the most creative force in the world is a menopausal women with zest." Said Woodward: "It’s hard to be zesty if your sleep is being interrupted every eight minutes."