What Causes Hot Flashes? Study Gives New Clues

Scientists are getting warmer in their attempts to zero in on what causes hot flashes, intense surges of heat and sweating that affect millions of middle-aged women in the years leading to menopause.

Studying rats, researchers at the University of Arizona College of Medicine have pinpointed a small region of the brain that may go awry during typical hot flashes, finding that a certain set of neurons acts as a virtual control switch for the problem when estrogen levels drop.

"I think the idea is to develop some alternate treatments for hot flashes, but how could we possibly develop appropriate treatments if we don't know what causes them?" said study author Naomi Rance, MD, PhD, a neuropathologist, professor and associate head of pathology at the university. "This is the first evidence these neurons have anything to do with [heat) regulation."

Scientists note, however, that research with animals often fails to provide similar results in humans.

An estimated 70% of women-along with some men—experience hot flashes, and previous research indicated the flashes originated in the hypothalamus, a section of the brain serving as the "switchboard" between hormone signals and the central nervous system.

University of Pittsburgh scientists published a study earlier this year showing that the parasympathetic nervous system-part of the autonomic nervous system, which regulates unconscious bodily functions such as heart rate and breathing–isn't working as efficiently as normal during a hot flash.

Study Details

In the more recent research, Dr. Rance and her colleagues created an animal model of menopause by using a toxin to deactivate a group of brain cells known as KNDY (pronounced "candy") neurons in rats. After these neurons were deactivated, the rats' tail skin temperature consistently lowered, suggesting that the neurons control the widening of the blood vessels known as vasodilation that lead to hot flashes by increasing blood flow to the skin. The rats' tail skin temperature rose after removal of their ovaries, which produce estrogen.

"Hot flashes are really episodic vasodilation," Dr. Rance explained. "You can see it—that's why people get red, because blood rises to the surface of the skin. Flushing is the body trying to get rid of that heat. Their core temperature is normal, so it doesn't make sense at all."

Current treatment for hot flashes includes estrogen replacement therapy, which is controversial because of potential health risks, including higher odds of certain cancers. Another option is selective serotonin reuptake inhibitors (SSRIS), which are best known as a treatment for depression.

Although the current research helps identify the basic biologic mechanism behind hot flashes, it may be years before scientists are able to develop new choices for treating them, Dr. Rance said.

The study appeared in the journal Proceedings of the National Academy of Sciences.

Expert Comments

Jill Rabin, MD, chief of ambulatory care and obstetrics and gynecology at Long Island Jewish Medical Center in New Hyde Park, New York, praised Dr. Rance's study as "groundbreaking and very well done."

"The study is done in rats, so it's really hard to (translate the results) into people, but it's very, very interesting," said Dr. Rabin, who also is head of urogynecology. "This issue has been looked at for a long time and this may open the wav, possibly, for a study in humans."