Laughter may not be the best medicine, but it can help, unless it provokes a rare fatal reaction, say researchers in a mostly lighthearted article.
British researchers reviewed studies from 1946 through 2013 to document the beneficial and harmful effects of laughter.
"Laughter is not purely beneficial," Robin Ferner from City Hospital Birmingham and J.K. Aronson of the University of Birmingham concluded in this week's issue of the British Medical Journal.
"It remains to be seen whether sick jokes make you ill, dry wit causes dehydration or jokes in bad taste cause dysgeusia," a distortion of the sense of taste.
For the article titled "Laughter and MIRTH (Methodological Investigation of Risibility, Therapeutic and Harmful)," the researchers said the benefits of laughter include:
- Reduced anger, anxiety, depression and stress.
- Reduced tension (psychological and cardiovascular).
- Increased pain threshold. Although Dr. Patch Adams advocates therapeutic clowning, hospital clowns had no effect on distress in children having minor surgery in one study.
- Reduced risk of heart attack.
- Improved lung function in patients with chronic obstructive pulmonary disease or COPD.
- Increased energy expenditure. The researchers estimated a day of "genuine laughter" could burn 2,000 calories.
- Reduced blood sugar levels in people with diabetes.
- Higher pregnancy rates after in vitro fertilization when a clown joked with would-be mothers.
But laughter can cause harms that are immediate and related to the dose, the researchers noted.
One woman with racing heart syndrome collapsed and died after a period of intense laughter.
Some other risks were:
- Protrusion of abdominal hernias — side-splitting laughter or laughing fit to burst.
- A quick intake of breath during laughing can cause foreign bodies to be inhaled.
- Trigger for asthma attacks.
The researchers also listed pathological causes of laughter, most commonly epilepsy (gelastic seizures.)
They said their search was limited to laughter without exploring related behaviour such as chuckles or grins.
"We infer that laughter in any form carries a low risk of harm and may be beneficial."
No funding was required. The authors said their senses of humour sometimes conflict.