"It's true that some people are naturally happy, and they tend to do better than others," Zautra said. "But even if you factor out different temperaments, it seems that people who are not as jovial can learn to better handle pain if they work toward improving their mood."
Of course, Hollywood has taken the issue to heart. The Robin Williams movie "Patch Adams," highlighted the approach of Dr. Hunter Adams, who made comedy part of his patients' medical treatment, donning a clown nose to help entertain patients.
Through the years, celebrities have a time-honored tradition to make hospital rounds to raise spirits, if only to build their own public image. But entertainment -- especially laughter -- is more and more becoming hospital routine.
On staff at New York's esteemed Memorial Sloan-Kettering Cancer Center is Dr. Stubbs the Clown, aka Michael Christensen, co-founder of the Big Apple Circus Clown Care Unit. Since 1986, he's spearheaded a program that has placed 93 clowns in 17 hospitals around the country, making 200,000 bedside calls a year.
Allison Crane, a nurse from Illinois, furthered the effort in 1987, founding the Association for Applied Therapeutic Humor. She had earlier belonged to a focus group called Nurses for Laughter and wanted to expand the program so that all health-care professionals could realize the healing benefits of humor.
Among the AATH's missions is to compile research, and among the most promising studies comes out of Loma Linda University in California, where doctors have been studying laughter's benefits on the immune system.
A 2000 study of 52 male medical students found that when they watched humorous videos, their stress levels, as measured by T-cell activity in the blood, tended to rise, according to Dr. Lee Berk. T-cells, also called "natural killer cells," jump-start the body's immune system by attacking viruses.
In another study, Berk followed two groups of cardiac patients through a yearlong rehabilitation program. All the patents received standard care. But one group also watched 30 minutes of comic videos each day. Berk found that laughter decreased disease-related symptoms, such as arrhythmias.
"It's more than a little ironic that we're quickly realizing just how important humor is to the healing process, because doctors have always had the reputation of being the most humorless of people," said Dr. Greg LeGana, who maintains a duel career in medicine and show business.
LeGana and fellow doctor Barry Levy, a school chum from New York's Cornell Medical College, created the New York cabaret show "Damaged Care," a musical comedy about the medical profession. They've performed before health-care professionals and general audiences throughout the country.
"Anyone who's ever made people laugh knows that they are soothing a soul," said LeGana. "It's great that research seems to be bearing out something we've always known in are hearts to be true."
For more information on the Association for Applied and Therapeutic Laughter, click here.
To learn more about the World Laughter Tour, click here.