MONDAY, March 7, 2005 (HealthDay News) -- A good belly laugh may have repercussions all the way up to the heart.
For the first time, researchers have found that laughter causes the endothelium, the inner lining of blood vessels, to dilate. This increases blood flow which, of course, is good for overall cardiovascular health.
The message is clear, and economical.
"I think it would be reasonable for everybody to loosen up, and spend about 15 to 20 minutes a day laughing," said lead researcher Dr. Michael Miller, director of preventive cardiology at the University of Maryland Medical Center.
Miller, who is presenting his findings Monday at the American College of Cardiology scientific sessions in Orlando, Fla., said he gets many of his chuckles from watching Jay Leno, Dennis Miller (no relation) or Frasier.
Which leads to the proposition that television may actually have a limited role in heart health "if you watch the right shows and spend your time watching comedies rather than stress-provokers," Miller cautioned.
Although this is the first study to show that laughter has such an effect, Miller had previously reported that people with heart disease generally responded to everyday life events with less humor than people who were healthy. And Harvard University researchers have reported that people with an optimistic outlook also have a reduced risk of heart disease.
For this study, 20 healthy volunteers were randomly assigned to watch 15 to 30 minutes of a light movie such as Kingpin, Something About Mary or excerpts from Saturday Night Live; or, on the heavier side, the Steven Spielberg war drama Saving Private Ryan. The participants were divided equally between men and women, averaged 33 years of age, and had had their initial blood flow measured after an overnight fast.
A minimum of 48 hours later, the volunteers came back and watched a second movie they had not seen previously.
"They watched both movies and served as their own controls," Miller said. That means the study eliminated confounding factors that can arise when comparing two separate individuals, he explained.
All told, the researchers made a total of 160 measurements of blood flow in the arm's brachial artery.
Almost all of the volunteers (95 percent) experienced increased blood flow while watching the funny movie, while three quarters (74 percent) had decreased flow while observing the ravages of war onscreen.
Overall, average blood flow increased 22 percent while laughing and decreased 35 percent during mental stress. The changes lasted 30 to 45 minutes after watching the movie segment.
The magnitude of the changes was similar to the benefit that might be seen with aerobic activity, Miller said. That's not a reason to trade laughing for exercise, he added; the ideal would be to do both.
It's not clear why laughter had this salubrious effect, but Miller has some ideas. "The endothelium has endorphin receptors so what may be happening after a good laugh is these endorphins are released and activate the receptors, causing an interaction or perhaps just an independent dilation of the endothelium," he said. Endorphins are "feel good" chemicals with morphine-like properties.
It's also possible that mental stress may lead to the release of stress hormones such as cortisol, which may then reduce the release of nitric oxide (not to be confused with the laughing gas nitrous oxide) from endothelial cells. This, in turn, could result in constriction of the vessel.
Whatever the reason, the message for cardiologists is clear. "We need to spend more time talking to patients about stress and the psychosocial aspects of illness," said Dr. Richard Hayes, clinical assistant professor of medicine at New York University Medical Center in New York City. "It's an under-evaluated part of illness."
For more laughs, visit the American Film Institute's list of 100 Funniest American Movies.