So good for you.© Punchstock

Does laughing make your heart healthier? It may sound funny, but doctors now say they have serious evidence to support the idea. A new study shows that enjoying a joke or two can improve the function of blood vessels.

Medical experts have warned about the effects of stress on cardiovascular health, and science backs up their concerns: When faced with a difficult situation, the body releases hormones that elevate blood pressure. These hormones, adrenaline and noradrenaline, produce this effect by causing blood vessels to constrict.

Left untreated, high blood pressure can lead to a stroke or a heart attack. Doctors often recommend that people with this condition take more time to relax during their workday and incorporate stress-busting physical activity into their life.

But less is known about psychosocial behaviours that can benefit the body's cardiovascular system.

Laughing matter

A study published in 2000 provided preliminary evidence that laughter can help the heart, says Michael Miller, director of preventive cardiology at the University of Maryland Medical Center in Baltimore.

In that study, he and his colleagues interviewed people who had either suffered heart attacks or undergone procedures to clear out clogged arteries. They found that these patients reported laughing less than those who did not have heart disease.

Miller has always been interested in laughter. As a child he kept a book of jokes, and his first cousin works as a stand-up comedian. So after the 2000 study connected amusement with good heart health, he decided to take a closer look at the possible relationship.

He and his colleagues decided to take a more direct approach this time around. Instead of questionnaires, they used an ultrasonic device to measure the diameter of the brachial artery, a main blood vessel that runs from the shoulder to the elbow.

The researchers asked 10 women and 10 men to watch 15-minute movie scenes that contained either nerve-racking or comical material. For the stressful scene, the team used the opening segment of Saving Private Ryan, which portrays a dramatic battle during the Second World War. The funny segment came from either of two slapstick comedies: King Pin or There's Something About Mary.

For good cardiovascular health, blood vessels should readily expand after being constricted. So before and after showing the movie scenes, the scientists applied pressure to each volunteer's brachial artery and tested how quickly it bounced back to its normal shape.

In 19 of the 20 subjects, the comedy seemed to have a beneficial effect. Overall, the blood vessel dilated 22% faster than normal after laughter, and 35% more slowly than normal following a stressful scene.

Although the negative effect of stress was anticipated, laughter produced a bigger positive impact than expected. "We thought that laughter would be pretty much neutral, but it actually produced a pronounced effect," says Miller. He presents the results today at a meeting of the American College of Cardiology in Orlando, Florida.

Funny movies

Miller says he now advises his patients to seek out a hearty laugh from time to time. "We've already started telling them to watch funny movies or seek situations that they find light-hearted," he says.

He and his fellow scientists cannot explain why laughter improves blood-vessel tone. It might have something to do with the release of endorphins, the same hormones that produce a "high" after exercise. Studies have revealed that endorphins help to repair blood vessels.

Another possibility is that laughter releases nitric oxide, a gas that relaxes part of the blood vessel wall known as the endothelium.

But the causes require further investigation. "Nitric oxide is released very locally in the endothelium. It would be fairly unusual for the endothelium to be globally stimulated by nitric oxide," says Ian Megson, an expert on blood vessels at the University of Edinburgh, UK.

Until this mystery is solved, Miller sees no problem in recommending laughter as medicine. "There's no downside to laughing," he says. 

Cardiologist, University of Maryland Medical Center, Baltimore

Cardiologist, University of Maryland Medical Center, Baltimore