Laughing appears to be almost as beneficial as a workout in boosting the health of blood vessels, a new study suggests. "Thirty minutes of exercise three times a week and 15 minutes of hearty laughter each day should be part of a healthy lifestyle," says Michael Miller of the University of Maryland Medical Center in Baltimore, US, whose team has shown that laughter relaxes arteries and boosts blood flow. He showed clips from the comedy movie King Pin to 20 volunteers. Before and afterwards, he made ultrasound measurements of blood flow and dilation in the brachial artery in the arm. The scans showed that in all but one of the volunteers, the volunteers' arteries relaxed and blood flowed more freely than usual for 30 to 45 minutes after the film. The opposite happened when the same people watched harrowing scenes from the war movie Saving Private Ryan. In 14 of the 20 volunteers, the artery wall constricted, reducing blood flow. Overall, blood flow decreased by 35% after the stressful clips and increased by 22% during laughter. The results suggest that laughter could help keep the lining of the arteries - the endothelium - healthy and thus reduce the risk of cardiovascular disease. At the very least, laughter offsets the impact of mental stress, which is harmful to the endotheliums.