Hormone therapy for hot flashes tied to lower heart risk when started within 10 years of menopause

Hormone therapy became a heart worry in the early 2000s, when the Women’s Health Initiative, or WHI, found that estrogen-plus-progestin pills raised the risk of heart disease and stroke. The volunteers in its hormone trials averaged 63, more than a decade past the average age of menopause.

Hot flashes and night sweats arrive much sooner. They build up through perimenopause and typically peak in early postmenopause, just after periods stop. Heart research on hormone therapy has mostly skipped the run-up, when hormonal fluctuations and symptoms are greatest.

A team from the University of Pittsburgh and Virginia Commonwealth University has now analyzed 20 years of health data from 2,737 women with hot flashes or night sweats. Writing in JAMA Internal Medicine, they report that starting hormone therapy during perimenopause or recently after menopause went with about a fifth fewer heart attacks, strokes and related events. The link was more pronounced in Black women and in those who began within 10 years of menopause.

Women’s Health Initiative data hinted early that hormone timing matters

The WHI asked a prevention question. Volunteers aged 50 to 79, all past menopause, took hormone pills or a placebo, an inactive pill, to see whether the drugs would protect the heart and bones. The pills did not prevent heart disease as was once thought, and the combined version also raised the risk of blood clots, breast cancer, and dementia. Years of reluctance from both patients and providers followed.

The same data held a clue. In 2007, WHI researchers re-sorted the results by years since menopause began. Participants within 10 years of menopause tended toward less coronary heart disease on treatment, and those 20 or more years out tended toward more. The trend fell short of the researchers’ own bar for ruling out chance, and the risk of stroke was elevated regardless of timing. That pattern fits what researchers call the timing hypothesis: that the cardiovascular effects of hormone therapy depend on when a woman starts it.

Yet no clinical trials have specifically evaluated heart risk from treating hot flashes with hormones during the menopause transition. The Pittsburgh and Virginia team calls its study the first of its kind in the United States to look at that question.

How 20 years of SWAN data were made to behave like a hormone trial

The data come from the Study of Women’s Health Across the Nation, known as SWAN, which enrolled 3,302 women at seven US research centers between 1996 and 1997. All were 42 to 52, still having periods and off hormones when they joined, with visits taking place approximately every year after that.

The analysis included the 2,737 participants who reported hot flashes or night sweats over the past two weeks, were free of cardiovascular disease and had never used hormone therapy. Of those, 755 started hormone therapy over the 20-year follow-up, at an average age of about 54. Their hormone use was verified from medication containers, which beats relying on memory. Heart attacks, strokes, heart failure and procedures to reopen blocked arteries were self-reported, and cardiovascular deaths were recorded from death certificates. There were 224 fatal and nonfatal events in all.

SWAN only watched, and nobody was told whether to take hormones. “By using data from the SWAN study, we essentially were able to emulate a series of hypothetical clinical trials,” said Samar El Khoudary, an epidemiologist at Virginia Commonwealth University and one of the senior researchers who led the study. Each one compared the starters with women who did not begin treatment at the same point. Everyone entered as a never-user, so long-time users who had already done well could not flatter the result.

The design has one blind spot: the women chose. “Women who elect to use hormone therapy differ from women who do not on multiple characteristics, such as race, ethnicity, socioeconomic position, and access to healthcare that this study cannot fully address,” said Rebecca Thurston of the University of Pittsburgh School of Medicine, also a senior researcher on the study. The authors write that “all estimates warrant caution given the potential for residual confounding”, meaning differences between the groups that the statistics could not remove. The published summary gives no breakdown by hormone type, dose or route and no absolute numbers for either side, and the full paper is paywalled, so this account rests on that summary. What is left is a carefully built observational estimate that still cannot show the hormones caused the difference.

Starting within 10 years of menopause tracked with a quarter fewer heart events

Across the whole cohort, the figure came to a 22% lower risk of cardiovascular events compared with not starting therapy. Timing sharpened the picture. Those who initiated hormone therapy within 10 years of menopause onset had an estimated 27% lower risk, roughly three events for every four among those who held off.

For those who started more than 10 years after menopause, the estimate tipped the other way, but its range ran from about a third lower to more than three times higher. That is too uncertain to count as harm or as safety.

Why timing would matter is unsettled. The team believes it may be linked to how arteries change with age. Estrogen helps keep blood vessels relaxed and open, and without it cholesterol may start building up on artery walls. A randomized trial called ELITE tested the idea on the arteries themselves, giving 643 healthy postmenopausal women the hormone estradiol or a placebo and measuring how fast the walls of their neck arteries thickened. Over about five years that process slowed on treatment in those less than 6 years past menopause, but not in those 10 or more years past it. Scans of the heart’s arteries showed no clear difference between the placebo group and the estradiol group, so ELITE backs the artery idea on one early warning sign and says nothing yet about heart attacks or strokes.

Race and ethnicity modified the link too. Black women who started hormone therapy had an estimated 49% lower risk, about half, while no clear effects were observed in White women or women of other races. The published summary offers no explanation for the gap. “The differences in cardiovascular outcomes by race and ethnicity are notable, particularly because Black women are more likely to experience severe vasomotor symptoms,” El Khoudary said, using the medical term for hot flashes and night sweats. A difference confined to one group needs repeating before it means much.

How the SWAN heart finding squares with trial data, the NHS and the FDA

The closest comparison came last year, when researchers went back to the WHI and looked only at participants with moderate or severe hot flashes. Among those aged 50 to 59, both hormone regimens appeared to have neutral effects on heart and artery disease, while those aged 70 and older had increased risks. Those volunteers were all past menopause and on fixed daily pills, while SWAN’s participants started earlier, on treatment they chose.

Set side by side, the two agree on what matters most to a woman deciding around menopause: starting hormones in that window showed no sign of harming the heart. They part ways on whether it helps.

Regulators and health services already lean toward the reassuring half. The FDA began removing boxed-warning language about heart risks, breast cancer, and probable dementia from hormone therapy labels in November 2025, and its labeled recommendation will be to start within 10 years of menopause onset or before 60 years of age. The NHS says that taking hormone replacement therapy (HRT) has little or no effect on the risk of getting coronary heart disease. For those under 60 with menopause symptoms who are not at high risk of breast cancer or blood clots, it says the benefits of HRT are likely to outweigh the risks.

The authors are explicit that their findings should not be used to support hormone therapy for preventing heart problems. For a woman weighing hormone therapy for hot flashes, the choice still turns on her symptoms and on other risks, including the increased breast cancer risk observed with a longer duration of use. That is a conversation for a clinician who knows her history.

The heart is looking less like a reason to avoid hormone therapy started early, and it is still no reason to start.