Hot
Flashes: Exploring the Mystery of Women's Thermal Chaos
By DENISE
GRADY
 here
comes a time in many a woman's life when she must cast off her
garments, fling open windows, toss back blankets and ask repeatedly,
Is it hot in here? Even her fondest friends and relatives may find
it hard not to laugh.
Hot flashes are pretty funny, as long as they are happening to
someone else.
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Of the many little adventures that accompany menopause, hot
flashes are the most common — affecting as many as 80 percent of
women — The rush of heat, the drenching sweat and the telltale
flushed face last only a few minutes, but they can recur 10 times a
day and several times a night. And the pattern can drag on for
years. Is this nature's idea of a joke?
The causes of such thermal chaos are only partly understood. A
hot flash is a sudden, intense version of what the body normally
does to cool down when it is overheated: blood vessels near the skin
dilate to dissipate heat, and the person breaks into a sweat. The
tactic works so well that after a hot flash, many women feel
chilled.
But why, when a woman is sitting at her desk or driving down Main
Street, does her body suddenly think it is overheated? The answer is
not clear. One basic fact has been known for decades: hot flashes
are linked to declining estrogen levels. In women who have their
ovaries removed surgically, the effect can be almost immediate. Some
actually begin having hot flashes in the recovery room. And
regardless of whether flashes are brought on by surgery or natural
menopause, estrogen replacement therapy quickly stops them in most
women.
Hot flashes are common in the United States, Australia and
Western Europe, but are said to occur less often in Asian women. But
no knows whether Asians really have fewer flashes, or just report
them less. If they do have fewer, whether the difference is due to
diet, genetics or both is not known.
In fundamental ways, hot flashes remain a mystery. They must
originate in the brain. Body temperature is regulated there, in a
region called the hypothalamus. But no one knows exactly how
estrogen, or the lack of it, acts on that region. Nor is it known
why one woman sweats through a dozen flashes a day while another,
with the same flagging estrogen levels, stays cool. Similarly,
doctors do not know why, in most women, the symptoms eventually go
away on their own. And if hot flashes have a purpose or a health
benefit, scientists have yet to figure out what it might be.
The unanswered questions have become more important recently, as
mounting evidence has cast doubt on the safety of hormone
replacement, especially for long-term use. Hormones are the most
effective treatment for hot flashes, but many doctors and patients
have begun to question whether taking them just to relieve symptoms
is worth the risks, which include slightly increased odds of heart
attack, stroke, breast cancer, blood clots and gallbladder disease.
Women want safer alternatives, and although a better understanding
of hot flashes may lead to better treatments, so far no great
breakthroughs have occurred.
Dr. Robert R. Freedman has been studying hot flashes for about 20
years at Wayne State University in Detroit, where he is a professor
of psychiatry and obstetrics and gynecology. The National Institutes
of Health has supported his work, he said, but not many other
scientists have taken up the cause, and he wishes more would.
"Science gets better with more people working on it," he said.
Before he became interested in hot flashes, Dr. Freedman was
trying to find out whether biofeedback could help people with
Raynaud's disease, which causes very cold hands and feet. One of his
students, whose mother had severe hot flashes from the breast cancer
drug tamoxifen, which blocks the action of estrogen, said, "I know
you can make cold people warm, but can you take hot women and make
them cold?" Dr. Freedman was intrigued.
Most of his studies have been in humans, he said, noting that
"rats are a lousy model of menopause." Rats reproduce until they die
and do not have menopause. An artificial menopause can be induced
with drugs or surgery, but even then it is not clear whether the
rats have hot flashes, he said.
"People have measured changes in tail temperature that they
assume are flashes, but I don't buy it at all," Dr. Freedman said.
Researchers, he added, do not know whether other animals have hot
flashes, including female monkeys and apes, though he hopes to study
them.
Dr. Freedman and his colleagues study menopausal women, often
comparing those who have flashes with those who do not, though, he
said, it is hard to find menopausal women who do not have hot
flashes.
In the laboratory, the women are hooked up to equipment that
measures their skin temperature, sweating and other skin changes
that mark the start of a hot flash. In addition, the women swallow
radiotelemetry pills, which measure their core body temperature
every 30 seconds or so as they travel through the digestive tract.
In some experiments the women are given drugs that bring on hot
flashes or stop them, and some women stay in the laboratory
overnight so the researchers can measure hot flashes during sleep.
Most women who have flashes average six a night, Dr. Freedman
said, but, he added, "I saw a woman recently who had 17."
The overnight studies showed something surprising about the sleep
problems that many women have after menopause.
"The common thinking is that the hot flashes wake you up and
disturb your sleep, and you feel crummy in the morning," Dr.
Freedman said. "But we found that half the flashes don't have
wake-ups, and half the wake-ups don't have flashes. The insomnia is
not necessarily a product of the flashes."
He is conducting more sleep studies to try to decipher the
connection.
Dr. Freedman's experiments have found a major difference between
menopausal women who have hot flashes and those who do not. Women
without flashes have a "neutral" zone of about 0.7 degrees
Fahrenheit, and their core body temperatures can rise or fall in
that zone without making them shiver or sweat. The upper limit of
the zone is the threshold for sweating, and the lower limit the
threshold for shivering.
But in women who do suffer from flashes, the zone has shrunk so
much that it is almost nonexistent, meaning that even a tiny rise in
core temperature will cause a hot flash, and a tiny drop can cause
shivering.
But why is the neutral zone compressed to nothing? Dr. Freedman
and his colleagues theorize women who suffer from hot flashes,
compared with those who do not, have higher brain levels of a
hormone called norepinephrine, which can shrink the neutral zone.
The norepinephrine changes may be related to dropping levels of
estrogen, or to aging, or both, Dr. Freedman said.
In any case, too much norepinephrine seems to play a major role
in hot flashes. Studies in animals have shown that increased
norepinephrine shrinks the neutral zone, and experiments in people
show that a drug called clonidine, which lowers norepinephrine, can
expand the zone.
But for most women, clonidine has too many side effects to be a
good treatment for hot flashes, Dr. Freedman said, noting that it
can cause tiredness, dry mouth and low blood pressure. Some women
get relief from antidepressants like Paxil and Effexor that can
affect the hypothalamus. But so far, nothing works as well as
estrogen.
For women bothered by hot flashes who do not want to use drugs,
Dr. Freedman recommends using air-conditioning, wearing light
clothing in layers and keeping room temperatures low, because warm
environments can definitely bring on hot flashes. Cold drinks can
help ward off flashes. In addition, he has done studies showing that
the kind of deep breathing techniques taught in yoga classes can
reduce the rate of hot flashes by about half. The techniques require
training and practice, and he advises patients to take a yoga class
to learn them.
He has also tried, unsuccessfully, to get a grant to help a small
company make cooling sheets, similar to the ones used in hospitals
to treat fever. The cooling sheet would go on the mattress, under a
regular sheet, and the woman would lie on top of it.
"You could just stick it on your half of the bed, and you
wouldn't freeze your spouse," Dr. Freedman said.
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