London, June 5 (IANS) A dash of humour keeps people healthy and increases their chances of reaching the retirement age.

But after the age of 70, the health benefits of humour decrease, according to researchers at the Norwegian University of Science and Technology (NTNU).

The study is based on a comprehensive database from the second Nor-Trøndelag Health Study, called HUNT 2, which comprises health histories and blood samples collected in 1995-97 from more than 70,000 residents of a county in mid-Norway.

"There is reason to believe that sense of humour continues to have a positive effect on mental health and social life, even after people have become retirees," says project leader Sven Svebak, a professor of neuroscience at NTNU.

"The positive effect on life expectancy could not be shown after the age of 75. At that point, genetics and biological aging are of greater importance," he added.

Svebak and colleagues evaluated people's sense of humour with three questions from a test designed to measure only friendly humour.

He believes there are many myths and misunderstandings about humour. For example, one myth is that happy people have a better sense of humour than people who are more serious.

"But it is not enough to be full of laughter, as we say in Trøndelag. Humour is all about ways of thinking and often occurs in a process or in dialogue with others. It does not need to be externalised," he says.

"What people think is fun, is a different matter. Commonly, people with the same sense of humour tend to enjoy themselves together and can communicate humour without huge gestures. A twinkle in the eye can be more than enough," Svebak said.

These findings have just been published in the International Journal of Psychiatry in Medicine.