When laughing can be deadly

Laughter is the best medicine; or is it?

The benefits and harm linked to laughter have been documented in the British Medical Journal.

The article is part of the Christmas edition that intersperses scientific data with amusing asides.

The authors conclude that, after all their research, "it remains to be seen whether sick jokes make you ill".

The authors searched for medical articles written between 1945 and 2013 with the word "laughter".

Only 85 articles mentioned positive effects of laughter and 114 detailed the negative side effects.

"The benefits of laughter have often been assumed rather than demonstrated," argue the scientists.

They concede that a chortle does reduce tension, burns calories and lowers blood sugar in diabetics, but say "laughter is no joke".

The article mentions the case of a woman with a disease called racing heart syndrome who died in a fit of laughter.

Other harmful effects included a "jaw dislocation, headaches and instances in which laughter provoked asthma attacks".

There were records of the giggles causing hernias to became visible in children.

Diseases such as epilepsy can also provoke unnatural, pathological laughter, write the scientists.

Additionally, they argue that laughing people are more likely to breathe in germs or spread infectious diseases.

"The quick intake of breath that accompanies laughter can provoke inhalation of foreign bodies."

After listing all the harmful side effects of laughter, the authors then suggest that laughter may help people conceive children.

In an experiment in which women who had in-vitro fertilisation were entertained by a clown, 36% of the would-be mothers became pregnant compared with 20% in the control group who were not made to laugh.

As laughter lowers risk of heart attack, the authors said: "Reading the Christmas British Medical Journal could add years to your life."