That simple folk wisdom is also powerful science.

Research has shown that people under stress are more likely to get sick. Their wounds take longer to heal. They're more apt to be depressed, have high blood pressure and suffer heart attacks.

People who learn to control their stress, on the other hand, reap a host of health benefits.

They have fewer headaches. Their memories are better. They may even be less likely to get cancer, studies suggest.

And one of the best ways to fight stress, experts say, is something everyone does already -- they just don't do it very well.

It's breathing. And it's the key to many stress-reduction programs.

"What I tell people is, you take your lungs with you everywhere you go. So no matter where you are or what the situation, you can reduce your stress," says Alice Domar, director of the Mind/Body Center for Women's Health in Boston and an assistant professor of medicine at Harvard Medical School.

But only if you breathe deeply enough to make your belly and diaphragm move. That's something most adults don't do, say Domar and others.

"I have a new baby. She breathes diaphragmatically," Domar says. "We are all born breathing diaphragmatically."

Blame it on vanity

But most of us stop breathing deeply as we get older. We breathe using only our chests.

Why? A combination of vanity and social pressure, Domar says.

"Women hold in their stomachs. You can't breathe properly if you're trying to have a flat stomach," she says.

By the same token, young men are taught to stand up straight and puff out their chests. And as he ages, a man will often "suck in his gut" to hide a flabby midsection.

Our sedentary lifestyle doesn't help either, says Dr. James Gordon, director of the Center for Mind-Body Medicine in Washington, D.C., and a clinical professor of psychiatry at Georgetown University's School of Medicine.

"You walk into an office and you wonder sometimes if these people are alive," he says. "There's no movement. The breath is barely moving.

"It's a very serious problem."

Gordon has taught deep breathing to war refugees in Bosnia, to HIV-positive patients in the United States and to rural people in Africa.

"It is a universal language," says Gordon, who is also chairman of the White House Commission on Complementary and Alternative Medicine Policy. "People learn it and people get it -- because once you start doing it, you can see that it makes a difference."

Gordon says teaching people deep breathing and other stress-reduction methods "should be one of the central aspects of medicine."

"What's become clear in the last 20 to 25 years is that people who are stressed are more likely to develop a variety of illnesses," he says.

We all take thousands of breaths each day, and there's no special trick to turning some of them into deep breaths.

Gordon suggests these simple steps:

• Find a comfortable place to sit. Turn off the telephone and close the door. Sit with your feet comfortably on the floor.

• Breathe in through your nose and out through your mouth. Allow your eyes to close as your breath deepens so your belly begins to rise and fall.

• Begin with five to 10 minutes of deep breathing at a time, several times a day, and see how you feel. You can lengthen your sessions as you become more comfortable.

• If you find yourself too agitated to sit still, put on some music and dance. Or go for a walk. Then come back and try to sit quietly again.

This simple exercise could help you avoid some of the problems that have been identified by researchers like Janice Kiecolt-Glaser, who with her husband, Ronald Glaser, has done pioneering work on how stress affects the immune system.

Kiecolt-Glaser, director of the Division of Health Psychology at the Ohio State University College of Medicine, says stress has a "cascading negative effect" on the body's immune system.

In one study of medical students, for example, Glaser and Kiecolt-Glaser found that the stress of examinations caused a decrease in the activity of natural killer cells that fight tumors and viruses.

But students who were taught relaxation techniques -- and used them regularly -- showed significantly better immune responses than those who didn't use the techniques or only used them sporadically.

Similarly, Harvard's Domar taught relaxation techniques, including deep breathing, to a group of almost 300 women who had been having fertility problems.

Within six months after starting the program, 44 percent of the women were pregnant.

In another study, Domar worked with two groups of women who had been trying to conceive for one to two years. One group used mind/body relaxation techniques, the other didn't.

Within a year, 55 percent of the mind/body group were pregnant, compared to 20 percent of the control group.

"You're looking at almost tripling the take-home baby rate," Domar says.

But Dr. Paul J. Rosch, president of the American Institute of Stress, cautions that deep breathing may not be the answer for everyone.

"Stress is a highly individualized phenomenon," Rosch says. "And just as stress is different for everyone, there is no stress-reduction strategy that is a panacea.

"Deep breathing, jogging, yoga -- these are great for some people, dull and boring for others," he says. "You have to give subjects a smorgasbord of options and let them find out what works for them."

Instead of focusing on one stress-relief method, Rosch says, people should focus on identifying the cause of stress in their lives and preventing it.

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