Oh! what fun it is to write for the British Medical Journal's Christmas issue. In it, you can read about Richard Wagner's migraines, James Bond's alcohol-related health risks, and nominative determinism in The Brady Bunch.
As Popular Science reports, one of the special edition's studies "includes many interesting ways in which laughter is beneficial, as well as an odd list of harmful consequences." The heavily footnoted, pun-laden paper notes that in healthy people, 15 minutes of laughter could burn up to 40 calories, for example. Other benefits include improved lung function by clown-induced laughter for people with chronic obstructive pulmonary disease.
The authors are largely skeptical, though. From the study:
...laughter is no joke—dangers include syncope, cardiac and oesophageal rupture, and protrusion of abdominal hernias (from side splitting laughter or laughing fit to burst), asthma attacks, interlobular emphysema, cataplexy, headaches, jaw dislocation, and stress incontinence (from laughing like a drain). Infectious laughter can disseminate real infection, which is potentially preventable by laughing up your sleeve.
The authors disclosed funding ("none was required") and conflicts of interest ("their senses of humour sometimes conflict").