Lacking a sense of humor might not just be bad for your social life, it might also be harming your cardiovascular health. A new study shows that laughter actually increases blood flow in the body, proving right the old adage that laughter is the best medicine, at least when it comes to the heart.

Cardiologist Michael Miller and colleagues at the University of Maryland tested blood flow in 20 healthy men and women after they watched 15-to-30-minute clips of the comedy movies Kingpin and There's Something About Mary and a stressful film, the opening sequence of Saving Private Ryan. The researchers measured blood flow both before each viewing and one minute after it ended. "We wanted to see whether laughter induced a vascular response," Miller explains.

Prior research inspired the team to conduct the experiment. A series of questionnaires administered to sufferers of coronary heart disease by the cardiologists revealed that patients who had suffered a heart attack failed to find the humor in a situation, such as wearing the same outfit to a party, 40 percent more often than their healthy counterparts. "We didn't know whether that was cause and effect or just part and parcel of having the disease," Miller says.

They decided to investigate the possible healthy effects of laughter by measuring vascular dilation after people chuckled at funny bits or reacted to intense images. In total, the researchers gathered 160 measurements of blood flow in the brachial artery, which connects the shoulder and elbow, from the 10 men and 10 women. While laughing, 19 of the subjects increased healthy blood flow by an average of 22 percent. And comparing the amused and stressful states brought on by film clips, more than 50 percent more blood flowed when laughing, according to the paper published in the current issue of Heart.

In fact, being light-hearted boosted blood flow about the same amount as light exercise or drugs that lower cholesterol. Drama-induced stress, on the other hand, cut that rate by as much as angry memories or mental calculations. "What that suggests, at the very least, is that laughter on a regular basis will undo some of the excess stress we face in our everyday lives," Miller notes. "Patients at risk for cardiovascular disease should loosen up a bit."