Mom said it, editor Norman Cousins wrote it, and now researchers are proving it: Laughter is the best medicine. A good belly laugh boosts the body's immune system and reduces hormones that cause stress. A positive state of mind helps keep healthy people well and helps the sick recover.

"Silliness is very serious stuff," says Dr. Lee Berk, one of the USA's foremost researchers on humor and health. "This is not alternative medicine, this is real medicine," says Berk, of the Loma Linda University Medical Center, CA. The research "is not yet taught in traditional medical schools, but that is going to be changing," says Patty Wooten, the group's president, a nurse and author of Compassionate Laughter: Jest for Your Health (Commune-a-Key, $12.95).

Interest in the field was piqued in 1979 by Norman Cousins' Anatomy of an Illness. He got relief from pain from a degenerative disease when he guffawed his way through humorous videos. Cousins' book spurred the public and researchers to ask questions.

Some of the answers are being discovered by Berk and his partner, Dr. Stanley Tan, who tout the value of positive attitudes and "mirthful laughter." The two are pioneers in a field with a tongue-twister name: psychoneuroimmunology. Their lab tests show that after exposure to humor such as funny videos, there is a measurable decrease in subjects' stress hormones, including epinephrine and dopamine.

There is also a measurable increase in activity in the immune system. "It is astonishing to think that something so commonplace as laughter could manipulate significant immunological processes,” Berk says. In his review of the research, Montclair, N.J., psychologist Paul McGhee notes that frequent laughter relaxes muscles, helps control pain, may lower blood pressure and helps manage stress while increasing joy.

Researchers are very quick to say that mirthful laughter is no substitute for traditional treatments. "We are not telling people to stop their chemotherapy or their medication or not undergo surgery," Bittman says. "We just want people to harness all their resources, get themselves to a positive state of mind that can help them through this process."

A good sense of humor can also just get you through daily life with fewer psychic bruises, Wooten adds. Humor "serves as an inner safety valve that allows us to release tension, dispel worry, relax and let go."

Revised from an article by Karen S. Peterson, USA TODAY