Miller M, Mangano C, Park Y, Goel R, Plotnick GD, Vogel RA. Impact of cinematic viewing on endothelial function. Heart. 2006; 92:261-62

Chronic life stressors such as depression, anxiety, hostility, and anger may contribute to increased risk of coronary heart disease, in part by impairing endothelial function. Although coronary heart disease may also be associated with attenuated positive emotions as shown by reduced situational humor, little if any information is available regarding the potential impact of positive emotions on vascular reactivity. Because cinematic viewing evokes a range of negative and positive emotions, this study was designed to compare the effect of mental stress versus laughter on endothelial function. Studying 20 healthy young adults, researchers found that blood flow improved when they watched a movie that made them laugh. In fact, the circulation boost was similar to what has been seen with aerobic exercise. Exactly why laughing might give a boost to circulation is unclear. It is possible that it counters the effects that stress hormones can have on blood vessel function. In addition, laughter may spur the body's production of nitric oxide, a chemical that helps dilate blood vessels. The study involved healthy men and women who were tested using several noninvasive measurements of blood blow in the brachial artery. The measurements were taken before and after subjects watched clips from a comedy film and a distressing film. On average, the researchers found participants blood vessel dilation was more than 50% better after the comedy than after the depressing film. Many studies have linked negative emotions such as depression to poorer heart health. Researchers have speculated that persistent elevations in stress hormones may play a role.