Hot Flash Frequency May Match Circadian Rhythms


SAN DIEGO — Postmenopausal women with severe vasomotor symptoms show a circadian rhythm of hot flashes that peaks in the late afternoon and early evening hours, results from a small study showed.

“A lot of women complain about frequency of hot flashes at night,” Lauren Drogos said in an interview after her poster presentation at the annual meeting of the North American Menopause Society. “But we found that women were having the least frequent amount of hot flashes at night.

For the study, Ms. Drogos and her associates evaluated baseline data from a trial of 29 postmenopausal women who had at least 35 hot flashes per week and were enrolled in a clinical trial comparing the efficacy of hormone therapy, black cohosh, and red clover for menopausal symptoms and cognition. The women wore ambulatory sternal skin conductance monitors, which recorded their hot flashes over a 24-hour period. Hot flashes were defined as a greater than 2-micromho increase in skin conductance within 30 seconds. The women also kept a diary of their perceived hot flashes.

In an effort to reduce the interindividual variability in the time of hot flashes for study participants on different sleep/wake schedules, the researchers normalized the data to each woman's wake time.

The mean age of the study participants was 53 years, 61% were African American, 36% were white, and the rest were Asian American.

The women had an average of 19 hot flashes during the 24-hour monitoring period, including 14 during waking hours and 5 during sleeping hours, reported Ms. Drogos, a graduate student in the department of psychology at the University of Illinois at Chicago. “There was a broad peak of hot flash frequency, extending from late afternoon to evening hours, and a nadir that roughly corresponded to the time of the sleep episode,” the researchers wrote in their poster.

From a clinical standpoint, Ms. Drogos said, “if you have a highly symptomatic postmenopausal woman, you might want to advise her that her symptoms may peak at this time. If she has something important going on, advise her to plan accordingly by dressing in layers or packing an extra T-shirt in her bag.”

The pattern matchest “other circadian rhythms that generally follow this rise, such as core body temperature and peaks of cortisol levels,” she added.

Ms. Drogos acknowledged certain limitations of the study, including its small sample size and the fact that it focused on highly symptomatic women. “We want to do some follow-up studies, possibly looking at women who have shifted circadian rhythm, such as night shift nurses,” she said.

She reported no financial conflicts of interest.

Hot flashes were least frequent at night, with the peak occurring from late afternoon to evening hours.


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