A good belly laugh doesn't just make you feel good; it just might make your blood vessels work better, a new study has found.

The study's researchers found that emotions may be closely linked to blood vessel function. And they came to their conclusion after monitoring volunteers as they watched both funny and dramatic films.

Laughter appears to cause the tissue that forms the inner lining of blood vessels, the endothelium, to dilate or expand, in order to increase blood flow, the researchers at the University of Maryland School of Medicine in Baltimore found.

Emotionally-wrenching movies that produced mental stress, on the other hand, caused vasoconstriction – tightening of the blood vessels, which reduces blood flow.

The researchers say the findings suggest that laughter may do your cardiovascular system some good while mental stress will slow down blood flow.

"Given the results of our study, it is conceivable that laughing may be important to maintain a healthy endothelium, and reduce the risk of cardiovascular disease," says study leader Dr. Michael Miller, director of preventive cardiology at the University of Maryland Medical Center.

"At the very least, laughter offsets the impact of mental stress, which is harmful to the endothelium."

The beneficial changes that laughter brought were similar to the benefit seen with aerobic activity, says Dr. Miller.

"We don't recommend that you laugh and not exercise, but we do recommend that you try to laugh on a regular basis.

"Thirty minutes of exercise three times a week, and 15 minutes of laughter on a daily basis is probably good for the vascular system."

The study looked at 20 volunteers who had normal blood pressure, cholesterol and blood glucose levels. Each volunteer was shown a 15-minute segment of a movie – either a comedy, or a drama. The drama was the opening scene of "Saving Private Ryan", while the comedy was "King Pin." Forty-eight hours later, they were shown the other movie.

Brachial artery flow was reduced in 14 of the 20 volunteers following the movie clip that caused mental stress. In contrast, beneficial blood vessel relaxation, or vasodilation, was increased in 19 of the 20 volunteers after they watched the comedy.

Overall, average blood flow increased 22 percent during laughter, and decreased 35 percent during mental stress.

The blood vessel changes lasted for at least 30 to 45 minutes after the volunteers watched a movie.