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THURSDAY, June 26 (HealthDay News) -- Women tend to miss almost half their menopause-related hot flashes, which are associated with memory problems, according to a University of Illinois at Chicago study that included 29 women with moderate to severe hot flashes.

The women wore monitors that measured skin changes during a hot flash. Both subjective (self-reported) and objective (detected by the monitor) hot flashes were recorded over 24 hours. The average number of objective hot flashes was 19.5 per day, about 40 percent more than were reported by the women.

The researchers also measured the women's memory. Previous research has shown that about 40 percent of middle-aged women report forgetfulness.

"When we looked at the relationship between the hot flashes that the women truly had -- that is, the hot flashes that the monitor picked up -- and memory performance on the cognitive tests, we found a very strong relationship. So, the more true hot flashes a woman had, the worse her memory performance," lead author Pauline Maki, an associate professor of psychiatry and psychology, said in a prepared statement.

"In other words, the hot flash-memory relationship is not all in a woman's head. It's actually a physiological relationship that you can pick up on, if you measure hot flashes objectively with a monitor."

The researchers also noted a link between the total number of hours of sleep and memory performance the next day.

"The total number of hours slept predicted worse memory performance, but also the total number of hot flashes during the night when a woman was sleeping predicted memory dysfunction," Maki said. "So, the two together worsen memory in women the next day."

She said the findings suggest that treating vasomotor symptoms in women with hot flashes may improve their memory.

The study was published online in Menopause and was expected to be in the September/October print issue.

More information

The National Institute on Aging has more about menopause.