RALEIGH, N.C. — It has been said, "Laughter is the best medicine," but it may do more to help your health.

Comedy clubs are spread throughout the country. Eric Thal is the laugh leader from the World Laughter Tour. He was actually trained by a doctor on how to put people in silly, laugh-provoking situations.

"Children have the license to be silly. At a certain point, we become discouraged from that childish behavior, so we're kind of encouraging childish behavior," said Eric Thal, of the World Laughter Tour.

The childish behavior is being done for a very grown-up reason -- their health. It is no secret that laughter relieves stress, but new research shows it may even help the heart.

Researchers at the University of Maryland measured the blood vessels of 20 people. When put in a situation that caused mental stress, their blood vessels constricted. Over time, constant constriction can lead to the formation of heart-damaging plaque.

But when people laughed, researchers found the vessels actually relaxed.

"Vessels throughout the body, which expand and make it easier for the blood to flow," cardiologist Edgar Lichstein said.

The study on laughter was presented at this week's annual meeting of the American College of Cardiologists.