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Hot Flashes Only Disturb Sleep the First Half of the Night: Presented at NAMS

By Paula Moyer

SAN DIEGO, CA -- October 3, 2005 -- Menopausal hot flashes are more likely to wake women up during the first half of the night rather than the second half, according to study findings presented here September 30^th at the 16^th annual meeting of the North American Menopause Society (NAMS).

Because these sleep disturbances are more likely to occur in a room that is neutral to warm, the solution is to lower the bedroom temperature during the first half of the night, said principal investigator Robert R. Freedman, PhD, Professor, Departments of Psychiatry and Neuroscience, and Department of Obstetrics and Gynecology, Wayne State University School of Medicine, Detroit, Michigan, United States.

All people are roused more easily in the first half of the sleep cycle, while the body responds less to thermoregulatory signals in the second half of the night, when rapid eye movement (REM) suppresses such responses, Dr. Freedman explained.

"Hot flash-induced sleep disturbances appear in the first half of the night, when REM sleep is less frequent and not suppressing hot flashes," he said. "Some reports of poor sleep during menopause may be due to normal aging, but [are] misattributed to hot flashes."

He and his co-investigators conducted their study on the sleep quality in menopausal women because they had observed a discrepancy between the widely held belief that hot flashes cause sleep disturbances (supported by many epidemiologic studies) and findings in recent research in a sleep study that they conducted. He cited a probability sample of 589 subjects in which his team found that postmenopausal women actually had better sleep quality than premenopausal women.

His team conducted a sleep study involving 36 women. Among the women, 18 were postmenopausal and experiencing vasomotor symptoms; 6 were postmenopausal and asymptomatic, and 12 were perimenopausal. The studies took place on four consecutive nights in which the investigators varied the ambient temperature. The first night, the adaptation night, the temperature was 23° C (73° F) or neutral. On subsequent nights, the room was randomly set at 18° C (64° F) or cool, 23° C (73° F) or neutral, and 30° C (87° F), or warm.

The investigators wanted to see the relationship between hot flashes and the time of night that the subjects were awakened. Because of the concentration of REM sleep in the second half of the night, the investigators analyzed the data by halves of the night to determine the effects of hot flashes on sleep.

Among the 36 subjects, 13 were eliminated due to sleep disorders, hot flashes in presumably asymptomatic women, and previously undetected medical conditions such as hypertension. Among the 23 remaining women, the investigators detected "no group differences on any measure when analyzed by the whole night," according to Dr. Freedman.

The women had an average of 2.2 hot flashes per night in the first half of the night when ambient temperatures were neutral or warm. On the nights with cool ambient temperature, they had an average of 1.5 hot flashes in the first half of the night. The second half of the night was stable regardless of ambient temperature, with women experiencing an average of 2.1 hot flashes during that time. All women had more frequent REM during the second half of the night.

Among those experiencing hot flashes, the flashes themselves awakened them in the first half of the night. In the second half of the night, the women tended to awaken first, and then experience the hot flash.

Therefore, the investigators concluded that, "some reports of poor sleep during menopause may be due to normal aging, but misattributed to hot flashes."

Because of the high number of women screened out for previously undiagnosed sleep disorders, the findings also suggest that "reports of poor sleep may also be due to other disorders, such as apnea, restless leg syndrome, or fibromyalgia."


[Presentation title: Effects of Menopause and Hot Flashes on Objective and Subjective Sleep. Plenary session 5]

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