It's long been known that stress is bad for the heart but laughter, although light-heartedly related to good health on the basis that it reduces stress, has scientifically merited little credence to actually improving health in average people.

But now, says a report in Nature magazine, Cardiologists at the University of Maryland Medical Center, Baltimore, have found evidence that laughter really does improve health, even in healthy people.

After a study back in 2000 of people with heart-related illnesses proved that those with heart defects laughed less than those without, Michael Miller, director of preventive cardiology at the University decided to undertake more research.

Miller put together an experiment using a device to measure the diameter of a main artery in the arms of a group of volunteers exposed to either nerve-racking or comic movie clips

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

In 95% of the 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.

The researchers expected laughter to have a rather neutral effect but are pleased that the study shows enjoying a joke or two can demonstratively improve the function of blood vessels, and the reverse.

The cause of the improvement in blood-vessel tone is not understood but clearly there is no problem in recommending laughter as medicine.