LONDON Laughter can unleash the same changes in the body's chemistry as a quick bout of physical exercise, scientists claim. People who watched funny movies experienced the same hormonal changes that follow exercise, which are thought to boost appetite, they say. The findings could lead to the development of better ways to encourage healthy eating among patients who have gone off their food because of depression or other conditions.

The study builds on previous work which suggested that prolonged laughter can lower blood pressure and boost immune activity. “It may indeed be true that laughter is a good medicine,” said Lee Berk, who led the latest research at Loma Linda University in California.

In the study, volunteers were assigned to watch either a stressful or a humorous 20-minute video. The stressful video was the opening sequence of the 1998 movie Saving Private Ryan, which depicts a group of US soldiers landing on Omaha beach in the second world war. The other participants could choose between comedy movies and stand-up acts. A week after watching their first video, volunteers were shown the video of the opposite genre so their reaction could be compared.

Berk's team measured levels of two hormones, leptin and ghrelin - both linked to appetite - in the volunteers' blood. While the stressful film had no clear effect, the funny videos caused leptin levels to fall and ghrelin to rise. A similar effect has been observed after exercise and is believed to stimulate appetite.

The study does not prove that laughing improves appetite or fitness, but Berk said it “may provide ... further options for patients who cannot use physical activity to normalise or enhance their appetite”.

The work could benefit people in chronic pain and elderly patients, who can lose appetite, the researchers said. “We are finally starting to realise that our everyday behaviours and emotions are modulating our bodies in many ways,” said Berk.

Robert Provine, a psychologist at the University of Maryland and author of Laughter A Scientific Investigation, said it was difficult to untangle whether the physiological effects were caused by the act of laughing or something else. “An essential consideration about laughter is that it is a vocalisation that evolved to change the behaviour of other people, like talking. We do not have discussions about the health benefit of talking. Laughter did not evolve to make us healthy, although it may do so in indirect ways,” he told the Guardian.—Dawn/The Guardian News Service