Hot flashes and night sweats are the products of vascular changes — blood vessel constriction and dilation — that develop during the transition to menopause. These vasomotor symptoms, as they are known, affect up to 80 percent of women. They can last for between seven to 10 years.

The symptoms often become worse as perimenopause progresses. They peak in early post-menopause.

The unpredictable and unwanted flushes and sweats of menopause are one of the main reasons women seek hormone replacement therapy (HRT). It is the most effective treatment available for the relief of vasomotor symptoms.

Women who started HRT within 10 years of the onset of menopause had an estimated 27 percent reduced risk of cardiovascular disease.

Hormone replacement comes with some risks. Clinical trials in the early 2000s raised concerns that HRT could increase a woman's risk of heart disease, stroke and breast cancer.

More recent studies, however, have found that women younger than 60 years old who begin HRT close to the onset of menopause have a lower risk for heart disease than older women who start HRT later or don't take it at all.

To get a clearer picture of how taking HRT for hot flashes and other vasomotor symptoms during menopause affects a woman's risk for heart disease, researchers from Virginia Commonwealth University and the University of Pittsburgh analyzed 20 years of health data from more than 2,700 women enrolled in a large, ongoing observational study — the SWAN (Study of Women's Health Across the Nation) project.

None of the women in the study had a history of heart disease. More than 750 participants started taking HRT for vasomotor symptoms during the 20-year study period.

The data from the SWAN project let researchers mimic a series of randomized clinical trials, the gold standard in scientific research, Samar El Khoudary, a senior investigator on the study, told TheDoctor. “It allowed us to study clinically meaningful cardiovascular events in a population and for a length of treatment that has been challenging to study prospectively.”

The team reported that women who took HRT had a 22 percent lower risk of cardiovascular events such as congestive heart failure, heart attack and stroke than those who did not take HRT.

The protective effect of HRT on the heart and cardiovascular system varied according to the timing of HRT. Women who started HRT within 10 years of the onset of menopause had an estimated 27 percent reduced risk of cardiovascular disease compared to those who did not.

The researchers believe the declining health of blood vessels as women age may be one reason for this finding. One possible explanation is that, earlier after menopause, women may have less underlying vascular disease, whereas vascular changes such as plaque accumulation and arterial stiffness may become more common with increasing time since menopause. How these changes might influence the cardiovascular effects of menopause hormone therapy remains an area for further study.

Race and ethnicity also had an impact on the health effects of HRT. Black women who started HRT in peri- or early post-menopause had a 49 percent reduction of their risk for cardiovascular events. The researchers believe the findings are interesting because Black women are more likely than women of other races and ethnicities to experience severe vasomotor symptoms. “These findings highlight the need to better understand how HRT timing may influence cardiovascular outcomes across different races and ethnicities,” El Khoudary added.

“These findings should be interpreted carefully because this was an observational study, and we cannot determine from these data whether MHT itself caused the differences we observed,” said El Khoudary, chair of the department of epidemiology at the Virginia Commonwealth University School of Public Health. The study found that women who took HRT over a long period of time had a greater risk of breast cancer.

Black women who started HRT in peri- or early post-menopause had a 49 percent reduction of their risk for cardiovascular events.

Current guidelines advise women under 60 to start HRT within 10 years of the onset of menopause and take it for the shortest period of time possible. El Khoudary recommends that women talk to their providers about the risks versus the benefits of hormone replacement therapy for them since one's personal health history is an important factor.

The study and a related editorial are published in JAMA Internal Medicine.