"Conceivably, when you laugh you send a signal to the brain to release these endorphins, and these may activate receptors to release other chemicals, perhaps including nitric oxide, which is known to enhance blood vessel dilation," Miller said.
Laughter may also use similar mechanisms to help boost the immune system and reduce the amount of inflammation in the body, which has been linked to an increased risk of a host of health problems, said Lee Berk, an associate professor of health promotion and education who studies laughter at Loma Linda University in California.
(Patterson Clark -- The Washington Post)
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"Laughter is not dissimilar from exercise," Berk said. "It's not going to cure someone from stage three cancer, but in terms of prevention it does make sense. In a sense, we have our own apothecary on our shoulders. Positive emotions such as laughter affect your biology."
Other researchers said the findings add new insight into the interplay of emotions and health.
"This is just the latest example of the importance of the mind-body relationship," said Herbert Benson, who studies emotions and health at Harvard Medical School. "This shows that we have to look not only towards how to reduce stress but how we can elicit positive feelings, as well."
Heart specialists agreed.
"We've known that there's an association between state of mind and cardiovascular health," said Stuart Seides, associate director of cardiology at Washington Hospital Center. "This type of study gives us a peek into the mechanism."
Robert Provine, a University of Maryland psychologist who also studies laughter, was somewhat more cautious. It remains unclear whether the act of laughter was really at work in the movie-watching volunteers, since the researchers did not actually measure how much they laughed, he said.
"The results could be the result of just the act of watching the movie. Or maybe it's just the act of engaging in something interesting that doesn't cause stress," Provine said.
Miller acknowledged he has no way to know for sure that laughing per se produced the effect he measured.
"Is it laughing or just feeling good? We don't know at this time. But clearly laughter is an active process, and probably a good belly laugh will be better than just smiling. I think this active process helps release endorphins," he said.
Provine, despite his doubts about the study, is all for laughter.
"I strongly recommend laughter, based on the fact that a life of laughter is better than one without it," Provine said. "It feels better when you do it."
Miller envisions a time when doctors might recommend that everyone get 15 to 20 minutes of laughter a day in the same way they recommend at least 30 minutes of daily exercise.
"Wouldn't it be ironic if it turns out that laughing 15 to 20 minutes a day would be added as part of overall good health habits, like running?" Miller asked.
He added that he would not recommend that people replace their daily trips to the gym with a Marx Brothers movie, but they could consider adding activities that make them laugh.
"There's no downside that I know of to laughing," Miller said. "Based on these results, I am happy to recommend laughing to my patients."