Washington, Nov. 7 (Reuters): Laughter may be the best medicine, but even looking forward to having a good laugh can boost the immune system and reduce stress, US researchers reported on Wednesday.

Just anticipating a happy, funny event can raise levels of endorphins and other pleasure and relaxation-inducing hormones and lower production of stress hormones, a team at the University of California Irvine said.

“This stuff is real,” Lee Berk, an assistant professor of family medicine and researcher in complementary and alternative medicine who led the study, said in a telephone interview.

“This study shows that even knowing you will be involved in a positive humourous event days in advance reduces levels of stress hormones in the blood and increases levels of chemicals known to aid relaxation,” he said.

His team tested 16 men who all agreed they thought a certain videotape was funny. Half of them were told three days in advance they would watch it.

Those who knew in advance they would see the video started experiencing biological changes right away, Berk told a meeting of the Society for Neuroscience in Orlando, Florida.

When the men watched the video, levels of cortisol, a stress hormone, fell 39 per cent, Berk found. Epinephrine, also known as adrenaline, fell 70 per cent, while levels of the feelgood hormone endorphin rose 27 per cent and growth hormone levels rose by 87 per cent.

“Growth hormone is very beneficial to the immune system,” Berk said.

This all suggests that anticipation of a funny event can lower stress and stimulate the immune system, Berk said.

He said he had to work with a small group of similar men because he could not decide for them what would be funny. “Say you can’t stand Laurel and Hardy — watching a slapstick Laurel and Hardy video would be stressful for you,” he said.

“This group picked a fellow who uses the ‘sledgeamatic’ — a big sledgehammer and smashes fruit,” Berk added.

Berk and others had already shown that actually watching a funny video, or just laughing at a joke, could make healthful changes in the levels of hormones involved in stress and lower blood pressure. In 2000 a team at the University of Maryland reported that people who reported using humour more often were less likely to have had heart attacks.

But this is the first time that someone has shown anticipation of having fun has similar effects, Berk said.

“You have been thinking about it all day, so you experience a change in biology even before you get there,” Berk said. “That is therapeutic.”

Berk said the finding strengthens the advice that everyone lighten up a little to live longer. “Anticipation is half or two-thirds the fun,” he said.