More Hot Flashes Occur in Second Half of Night, Preliminary Data Shows

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Over half (59%) of hot flashes occur during the second half of the night during the rapid eye movement (REM) sleep cycle, according to a news release discussing the results of the study. A loss of REM sleep can lead to cognitive issues, a weakened immune system and cardiovascular disease, which is the leading cause of death for women in the United States, according to the American Heart Association.

This study was led by Sarah Witkowski, Ph.D., who is an associate professor at Smith College in Massachusetts. Her team studied roughly 60 perimenopausal women ages 43 – 54. Hot flashes were measured using sternal skin conductance, which uses electrodes attached to the sternum. Participants’ sleep time was measured using a sleep log which recorded time spent in and out of bed. To determine which was the first and the second half of the night, total in-bed time was divided by half.

Nocturnal hot flashes are one of the most common side effects of perimenopause. This is likely due to a drop in estrogen, which normally keeps blood vessels relaxed, cortisol levels controlled and plaque buildup reduced. Perimenopausal women are also at a higher risk of cardiovascular disease due to fluctuating hormone levels.

The first REM cycle of the night usually begins about 90 minutes after falling asleep. As the night progresses, the cycles become longer, giving ample time for hot flashes to occur. The average person should be in REM for about 2 hours a night. Thermoregulation is also reduced in REM sleep, which may be why hot flashes are more common during this time.

“This is preliminary data and on a small sample,” Witkowski said in the news release. “More research is needed to evaluate the association of hot flashes with sleep disruptions and how they may impact subclinical cardiovascular risk around the transition to menopause.”

The full details will be presented at the 2024 Annual Meeting of the Menopause Society held September 10 – 14 as part of the presentation, “Potential Implications for Cardiovascular Disease in Perimenopausal People: Investigating Differences in Nocturnal Hot Flashes in the First vs. Second Half of the Night.”