New Study Finds Link Between Hot Flashes and Breast Cancer

Two new studies suggest that the hormonal heat waves of middle age can help predict your risk of breast cancer and heart disease. Pat Wingert on menopause’s early warning system.

Like all things menopause, hot flashes are an unwelcome scourge for the middle-aged women who get them, ranging in intensity from merely bothersome to majorly disruptive to daily life. But could these mysterious waves of hormone-driven heat actually turn out to be a key predictor of future health? Two recent studies raise that tantalizing prospect.

The first, published this month and funded by the National Cancer Institute, found that women who experience hot flashes have a 50 percent lower chance of developing the most common types of breast cancer. It came right on the heels of a separate series of studies funded by the National Institutes of Health, which concluded that women who suffer from hot flashes also seem to be at higher risk of heart disease.

In short, menopausal hot flashes seem to be an early indicator that the sufferer can breathe a little easier about avoiding breast cancer, but should be extra vigilant when it comes to safeguarding her heart.

While none of these studies are conclusive—researchers need to replicate results to prove their conclusions are accurate—scientists are starting to rethink their long-held belief that hot flashes are a bothersome but benign rite of passage.

An estimated 70 to 80 percent of American women deal with hot flashes sometime during the menopause transition, but there is still a lot we don't know about them. The leading theory is that as a woman's hormone production declines, there's a change in brain chemistry that affects the hypothalamus, which controls things like blood pressure and body temperature. Small changes in ambient temperature can prompt the brain to over-react to signals that the body is overheated, resulting in a hot flash. Scientists speculate that hot flashes may also have a vascular component that affects the heart, while the very low levels of hormones that prompt hot flashes may protect against breast cancer.

Dr. Christopher Li, a breast cancer epidemiologist at the Fred Hutchinson Cancer Research Center in Seattle, said he became interested in a possible link between hot flashes and breast cancer because both are affected by a woman’s declining hormone levels. Between 2001 and 2005, Li and his team interviewed 988 women (ages 55-74) who had recently been diagnosed with breast cancer, and another 449 who had not.

The results, published this month in Cancer Epidemiology, indicated that those who had suffered from hot flashes had half the risk of developing invasive ductal and invasive lobular carcinoma, two of the most common types of breast cancer, as those who hadn’t. The study also indicated that the worse a woman's hot flash symptoms were, the lower her risk of developing breast cancer. “Women who experienced the most intense hot flushes—the kind that woke them up at night—had a particularly low risk of breast cancer,” said Li, the senior author of the study. The results held even after controlling for differences in persistence of symptoms, as well as age and type of menopause.

Researchers expected to find that a woman's use of hormone therapy (HT) would be a major confounder for all study participants, but it didn’t turn out that way. While as a group, women who use a combination of estrogen and progesterone are known to be at greater risk of developing breast cancer, Li said that in his study, having a history of hot flashes reduced that risk by half, compared to women who use HT but never experienced this menopausal symptom. (In the recent past, many women were mistakenly encouraged to use HT to reduce their future risk of heart problems.) While Li said his data should not be misinterpreted to encourage more women to use HT to treat hot flashes or be lax about mammograms, he is hopeful that it might open up a new area of research to determine “what it is about these types of symptoms, the timing, the rate, the severity, that makes them protective against breast cancer. Could we use this information for prevention or therapeutic uses?"

Hot flashes seem to be an early indicator that the sufferer can breathe a little easier about avoiding breast cancer, but should be extra vigilant when it comes to safeguarding her heart.

"We’re at the beginning of this story and we’re not sure yet where it will lead us,” he says, adding that hot flashes may prove "to have a silver lining." Li, who is finishing up a second, similar study, said more results will be available soon.

Meanwhile, emerging research funded by NIH as part of the Study of Women’s Health Across the Nation (SWAN) suggests that persistent and frequent hot flashes may be an early marker of adverse vascular changes associated with an increased risk of cardiovascular disease. One study published earlier this year in the journal Menopause found that women who had frequent and persistent hot flashes (occurring on a minimum of six days over a two week period, and lasting at least two years) are at higher risk of developing CVD, particularly if they are also overweight or obese. Study results indicate that the risk of CVD linked to persistent hot flashes is similar to that associated with smoking and obesity.

Lead researcher Rebecca Thurston, assistant professor of psychiatry and epidemiology at the University of Pittsburgh, said most researchers don’t think hot flashes cause changes that put women at higher risk for CVD, but may signal underlying vascular changes that need more attention. Diet may be a key piece of this, says Dr. Margery Gass, the executive director of the North American Menopause Society. Monkey studies indicate that eating an artery-clogging diet not only increases cardiovascular risk factors but prompts an earlier menopause. “There may be more toxic effects of these diets than we realized,” Gass says. “It could be that they are damaging the ovaries, which in turn, prompts the ovaries to make fewer eggs and follicles and less estrogen," perhaps leading to more severe hot flashes. Since heart disease takes decades to develop, persistent hot flashes may eventually be used to help doctors identify those at greatest risk of CVD at earlier ages.

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“The bottom line,” says Thurston, “is that hot flashes may be telling us something important about women’s health.”

Pat Wingert is a Newsweek correspondent based in Washington D.C. who covers society, politics, policy, education and health.