Some women get far more hot flashes than they realize.

A new study finds women in mid-life underreport the number of hot flashes they get by 40 percent. The problem seems to be linked to memory.

Hot flashes are a symptom of menopause. Previous research indicates that about 40 percent of mid-life women report forgetfulness, the researchers point out. The new study is the first to explore the relationship between objectively measured hot flashes and memory performance.

The researchers studied 29 midlife women with moderate to severe hot flashes. The women wore monitors that measured changes in skin conductance during a hot flash. Both subjective and objective hot flashes were recorded during a 24-hour period. The average number of objective hot flashes was 19.5 per day.

The researchers also measured memory performance — the recollection of words, names, word pairs, paragraphs and stories — using standard neuropsychological tests.

"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," said Pauline Maki at the University of Illinois at Chicago. "So, the more true hot flashes a woman had, the worse her memory performance."

The results will be detailed in the September/October issue of the journal Menopause.