Hot flashes that bedevil many women in menopause might actually be a good thing, depending on when they strike, according to new data from a long-running government study.
Women who had hot flashes at the start of menopause but not later seemed to have a lower risk for heart attack and death than women who never had hot flashes, or those whose symptoms persisted long after menopause began.
By contrast, among the few women who developed hot flashes late — in some cases many years after menopause began — there were more heart attacks and deaths when compared with the other groups.
The research involved more than 60,000 women followed for an average of almost 10 years. It's the first to examine timing of menopausal symptoms and subsequent risks for heart problems and deaths, said co-author Dr. JoAnn Manson, chief of preventive medicine at Harvard's Brigham and Women's Hospital.
Recent studies linked hot flashes with higher blood pressure and cholesterol levels, which could suggest a higher risk for heart problems, but the new research offers a more detailed look, Manson said.
Lead author Dr. Emily Szmuilowicz, an endocrinologist with Northwestern University's medical school, said the results should reassure millions of women who experience hot flashes or night sweats, which are essentially hot flashes that can be bothersome enough to awaken women.
The results suggest "there may be a positive side" to having these annoying symptoms, Szmuilowicz said.
The study was released online Thursday in the journal Menopause.
Dr. Elsa-Grace Giardina, a Columbia University specialist in women's heart disease who was not involved in the study, said the research has several limitations and that more rigorous study is needed to prove the results.
Few women developed hot flashes long after menopause began, and for at least some, previous use of hormone pills may have increased their risks for heart problems, Giardina said.
But more than one-third of the women with late-onset symptoms never used hormones, and Szmuilowicz said the researchers took past hormone use into consideration and still found timing of symptoms played a role.
Menopause occurs when women stop having periods and estrogen levels dwindle. Most women experience symptoms including hot flashes that can last for several years. But they don't usually persist indefinitely or begin long after the beginning of menopause.
Hot flashes aren't well studied but are thought to result from blood vessels dilating in response to the normal hormone fluctuations of menopause, Manson said. If they occur long after menopause begins it could signal a blood vessel abnormality that could also affect the heart, she said.
The research involved 60,027 women from the ongoing Women's Health Initiative observational study, examining disease risk factors and health outcomes and funded by the National Institutes of Health.
Women were in their early 60s on average, about 14 years past the start of menopause, when they answered questionnaires about their health, education history, and symptoms including hot flashes and night sweats. Cardiovascular problems and deaths were tracked during almost 10 years of follow-up.
More than one-third, or almost 25,000 women, had early symptoms — hot flashes at the onset of menopause that had stopped before they enrolled. Just 1,391 had late symptoms — hot flashes at enrollment but not at the start of menopause.
About 2.5 percent of women with early symptoms had heart attacks, compared with 3.4 percent of women with no symptoms and 5.5 percent of those with late symptoms. Also, about 6 percent of the early symptom women died, versus 11 percent of the late symptom group and 8 percent of the symptomless women. Women who had persistent hot flashes throughout menopause had risks similar to those without symptoms.
Giardina noted that high blood pressure, high cholesterol, diabetes and obesity — which all can contribute to heart problems — were more common among the late symptom women.
But the researchers said they accounted for that and still found that timing of menopause symptoms played a role in later heart attacks and deaths.
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