We all want to believe that laughter is good for what ails us, but the science backing that up is thin. Most studies have been small and have relied on self-reported assessments.
Still, a rollicking good guffaw can't hurt. Or can it? There are rare instances of laughter prompting an asthma attack and even rarer instances of it triggering a stroke. And though this hasn't been part of a formal study, one researcher speculates that if you're surrounded by people laughing inappropriately—finding, say, a cockfight hilarious—it increases stress.
However, a few studies relying on laboratory testing do show some benefits.
"A good belly laugh leads to the release of endorphins from the brain," says Michael Miller, director of the Center for Preventive Cardiology at the University of Maryland Medical Center in Baltimore.
That release sets off a cascade of heart-healthy biological events. Endorphins, pleasure-inducing neurotransmitters, activate receptors on the surface of the endothelium, the layer of flat cells lining blood vessels. That leads to the release of nitric oxide, which widens blood vessels—increasing blood flow, lessening inflammation, inhibiting platelet clumping, and reducing the formation of cholesterol plaque.
A 2005 study by Miller measured the blood flow of 20 volunteers before and after watching a funny movie and a sad movie. After the sad movie, blood flow was more restricted in 14 of the 20 viewers. But after the movie that made them laugh, average blood flow increased by 22 percent.
"The best laugh is one that brings tears to our eyes," says Miller, author of Heal Your Heart: The Positive Emotions Prescription to Prevent and Reverse Heart Disease, scheduled for publication by Rodale Press in September. His prescription: at least 30 minutes of exercise at least three times a week—and 15 minutes of daily laughter.
You Have to Laugh Out Loud
Funding for laughter and humor research is low—so low that when Mary Bennett, director of the Western Kentucky University School of Nursing, wanted to look into the effect of laughter on the immune system, she found herself scrounging, asking other researchers for vials and other equipment from their labs. "It's really hard to get taken seriously when you say you study laughter," she says.
But her study of 33 healthy women, published in 2003, showed that those who laughed at a humorous movie had higher levels of natural killer cell activity, which increased their ability to fight off disease. However, the effect was seen only in the subjects who laughed out loud, not in those who quietly watched the comedy.
A study in Japan that also used laboratory findings found that laughter could improve anti-inflammatory factors in the blood of people who have rheumatoid arthritis.
But the bulk of the research on laughter and health depends on subjective studies and not on evidence-based science. And some studies are contradictory. One study of 70 depressed elderly women found that laughter yoga was just as effective as exercise therapy in improving mood, as measured by self-satisfaction reports by subjects. Humor and laughter may improve muscle tone, though only when someone is laughing, and some studies do show that a good laugh can help reduce stress hormones. But other studies show that laughter doesn't affect those hormones, according to a review of the literature published by Bennett.
No doubt, a New Yorker cartoon, a good joke, or an hour spent with the Marx Brothers can feel therapeutic. But when Bennett, who has spent much of her career studying laughter and poring over the research literature, is asked whether laughter cures or prevents any disease, her quick answer is a simple "No."
Still, she adds, "I think it's a useful adjunct of real medicine. If you're going through something like chemotherapy, anything you can do to help you stay sane through something that nasty will help."