Are Hot Flashes Just A Nuisance?

TL;DR: Every night you sleep through a hot flash, your heart is on high alert, your blood pressure spikes, and blood flow to your brain is transiently reduced. Over time, in women with frequent nocturnal hot flashes, these events leave measurable marks on the brain’s vascular structure, visible on MRI as white spots, early signs of cerebrovascular disease. The hot flash you have learned to live with is an alarm trying to get your attention to take action.

This week I met a lovely woman for the first time. 53 years old, perimenopausal, has been having hot flashes for the last couple of years. They were infrequent at first, more frequent now. She is a business owner and by all accounts, a successful one. We were having a lovely conversation when she said something that made me feel a familiar flash of frustration.

“I want to stay natural.”

There it was. The amorphous fear lurking under the surface of many women’s consciousness about hormones. This is the enduring legacy of the Women’s Health Initiative study that published results in 2002.

Never mind that most of the incorrect conclusions promulgated with great fanfare have been walked back in the last 20 years. Never mind that many doctors and influencers now talk about nothing other than the critical importance of hormones in a woman’s body and brain.

Her only symptom was hot flashes, mostly mild. That is how she had been able to go a few years without doing anything about them.

“They’re not that bad,” she said. “I’ve gotten used to them. I don’t really think I need to address them, but if there’s something easy I can do, I’d consider it.”

What she did not know is that the hot flash is simply an announcement, an alarm, from the brain that estrogen has fallen below a critical level. That decline in estrogen has been silently reshaping her brain, her cardiovascular system, and her metabolism for years, with or without her awareness.

What Happens During a Hot Flash

Deep in the brain sits a thermostat. Before perimenopause, that thermostat operates within a comfortable range, a thermoneutral zone, wide enough to absorb small fluctuations in core body temperature without reacting. Estrogen plays a direct role in maintaining that buffer, acting on the hypothalamus to keep the zone wide enough that normal temperature variation is simply ignored.

As estrogen declines, the thermoneutral zone narrows. In some women it narrows dramatically. Research by Freedman showed that in symptomatic women, a rise in core body temperature of as little as 0.01°C, a fluctuation that would previously have been absorbed without consequence, can now trigger a full heat dissipation response. The thermostat has become a hair trigger.

The response it triggers is significant. Blood vessels near the skin surface dilate rapidly, flooding the skin with warm blood to radiate heat outward. Sweat glands activate. The heart rate picks up to compensate for the sudden redistribution of blood away from the core. Core blood pressure drops transiently as blood moves to the periphery.

What the woman feels is not the temperature rise that triggered the event. She experiences the full cascade of the heat moving outward through her chest, neck, and face, the sweat, the heart working harder, and then the temperature drop that follows as heat dissipates, sometimes leaving her chilled within minutes.

The whole sequence lasts anywhere from two to ten minutes and is measured by a sudden rise in sternal skin conductance, the electrical signature of sweat gland activation on the chest wall.

The findings are concerning.

What Nocturnal Hot Flashes Do to the Heart

In a landmark 2019 study published in the journal Sleep, Baker and colleagues monitored 86 women in the menopausal transition using simultaneous polysomnography, sternal skin conductance, and beat-to-beat blood pressure and heart rate measurement across 542 individual nocturnal hot flash events.

They found that hot flashes associated with arousals and awakenings accounted for 51% of all nocturnal hot flash events. These were accompanied by an approximately 6 mmHg increase in systolic blood pressure, a 5 mmHg increase in diastolic blood pressure, and approximately a 20% increase in heart rate, sustained for several minutes, in women who may not even remember waking. ¹

Critically, all categories of nocturnal hot flashes, including those that did not cause awakening, showed evidence of increased cardiac sympathetic activity. Even when the woman slept through the event entirely, her heart was on high alert.

The Second Half of the Night

At the 2024 Annual Meeting of the Menopause Society, Witkowski and colleagues presented preliminary findings from a study of approximately 60 perimenopausal women monitored using sternal skin conductance. They found that more hot flashes occur in the second half of the night, when REM sleep cycles are longest and most frequent, concentrating cardiovascular disruption precisely in the phase when the body is doing its most critical overnight work of restoration. ²

This matters enormously. REM sleep is the phase in which the brain consolidates memory, processes emotion, and performs critical restorative work. It is also the phase in which the cardiovascular system undergoes its most significant recovery with blood pressure dipping, heart rate slowing, and the nervous system quietening.

A hot flash that triggers a 20% increase in heart rate and a 6 mmHg blood pressure spike during that recovery window is a significant disruption. It is an interruption of the most restorative hours of the night, happening as the woman sleeps.

What Hot Flashes Do to the Brain

The cardiovascular activation during a hot flash does not stay in the heart. It reaches the brain.

When blood moves rapidly to the periphery during a hot flash, central blood pressure drops transiently. Cerebral perfusion depends on adequate blood pressure. When that pressure drops, blood flow to the brain drops with it.

In a 2013 study published in Menopause, Lucas and colleagues measured middle cerebral artery blood flow in real time using transcranial Doppler during spontaneous hot flashes in healthy postmenopausal women. The hot flash caused pronounced transient reductions in brain perfusion, even while women were lying still and supine. ³ In over 60% of the hot flash events studied, the reduction in cerebral blood flow exceeded what could be explained by normal biological fluctuation. The researchers concluded that the hot flash can present a significant physiological challenge to brain blood flow. ³

A transient reduction in cerebral perfusion that happens multiple times per day and night over months and years likely has consequences beyond our current understanding. Coincidentally, the middle cerebral is also the most affected artery in approximately half of all cases of stroke in women.

The accumulating effect of this has been documented at the level of brain structure. In a study led by Dr. Rebecca Thurston at the University of Pittsburgh, 20 midlife women underwent ambulatory hot flash monitoring alongside MRI brain imaging to assess white matter hyperintensities. These are bright spots on brain scans that reflect disease of the brain’s small blood vessels and are associated with increased risk of stroke and cognitive decline. More menopausal hot flashes, particularly those occurring during sleep, were associated with a greater burden of these white spots. ⁴

The women in this study did not have diagnosed cardiovascular or cerebrovascular disease. They were not even high risk by conventional measures. But they still showed a relationship between their nocturnal hot flashes and measurable changes in their brain’s vascular architecture.

This is the biology behind the brain fog, the word retrieval difficulties, the cognitive drag that women report and are routinely told is stress, aging, or overwork. It may not be any of those things. It may be the cumulative effect of a brain intermittently deprived of optimal blood flow, multiple times per night, for years.

What Hot Flashes Do to Blood Vessels

The cardiovascular signal from hot flashes goes beyond acute events during sleep. It appears in the walls of the blood vessels themselves.

In a rigorously conducted study published in Menopause in 2017, Thurston and colleagues measured endothelial function in 272 midlife women using both physiologic hot flash monitoring and ultrasound of the brachial artery. Endothelial function is a measure of the ability of blood vessel walls to dilate in response to increased flow. Among younger midlife women, frequent hot flashes were associated with poorer endothelial function, independent of every other measured cardiovascular risk factor. ⁵

Endothelial dysfunction is the earliest detectable stage of atherosclerosis. It precedes plaque formation, increase in blood pressure and diagnosis of cardiovascular disease by decades. In younger midlife women with frequent hot flashes, it was already present.

The hot flash may be the first signal that vascular dysfunction is beginning and may be an early marker of its trajectory.

Are Hot Flashes Just A Nuisance?

My patient told me her hot flashes were not that bad. She had learned to live with them and did not see them as a medical issue requiring attention.

She is hardly unusual. The medical advice she has ambiently picked up from her environment has told her that hot flashes are a quality of life issue, bothersome but benign. That framing has done her a significant disservice.

The research tells a different story. Each nocturnal hot flash is a cardiovascular event. Each one that causes arousal comes with a blood pressure spike, a heart rate surge, and an interruption of cardiovascular restoration during the body’s most restorative hours. Even those that don’t wake her are not neutral for her heart. Hot flashes can also cause transient reductions in cerebral blood flow. Over time, in women with frequent nocturnal hot flashes, these events appear to leave measurable marks on the brain’s vascular structure.

I shared this information with her. She received it in silence, deciding whether she felt educated or alarmed.

If you are reading this and you have made peace with your hot flashes, I want you to reconsider that peace. Your hot flash is trying to tell you something.

References

Baker FC, Forouzanfar M, Goldstone AM, et al. Changes in heart rate and blood pressure during nocturnal hot flashes associated with and without awakenings. Sleep. 2019;42(11):zsz175. doi:10.1093/sleep/zsz175
Witkowski S, et al. Potential implications for cardiovascular disease in perimenopausal people: investigating differences in nocturnal hot flash timing. Presented at the Menopause Society Annual Meeting, September 2024. (Preliminary data, approximately 60 participants.)
Lucas RAI, Ganio MS, Pearson J, Crandall CG. Brain blood flow and cardiovascular responses to hot flashes in postmenopausal women. Menopause. 2013;20(3):299–304. doi:10.1097/GME.0b013e31826e45f0
Thurston RC, Aizenstein HJ, Derby CA, Sejdic E, Maki PM. Menopausal hot flashes and white matter hyperintensities. Menopause. 2015;22(12):1274–1279. doi:10.1097/GME.0000000000000506
Thurston RC, Chang Y, Barinas-Mitchell E, et al. Physiologically assessed hot flashes and endothelial function among midlife women. Menopause. 2017;24(8):886–893. doi:10.1097/GME.0000000000000857

About the Author:

Dr. Manna Semby, ND

Functional Medicine Practitioner & Wellness Expert

Dr. Manna Semby, ND, IFMCP, MSCP, is a naturopathic and functional medicine doctor based in San Diego, California. She is the only doctor in the San Diego area who is both a Menopause Society Certified Practitioner and certified in the ReCODE 2.0 Protocol for preventing and reversing Alzheimer’s disease and dementia. She is also is a MoCA certified administrator. With over ten years in medicine, Dr. Manna has helped many women reverse early stages of cognitive decline through comprehensive brain, bone, metabolic, and midlife hormone medical care. She draws on years of clinical training and ongoing professional development to translate complex medical insights into practical, real-world precision medicine guidance.

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