Just in time to protect patients from the dangers of holiday cheer, a new scholarly review from a British medical journal describes many harmful effects of laughter.
Among the alarms it sounds: The force of laughing can dislocate jaws, make hernias protrude and cause asthma attacks and headaches. It can provoke cardiac arrhythmia, fainting and emphysema (this last, according to a clinical lecturer in 1892).
Laughter can trigger the rare but possibly grievous Pilgaard-Dahl and Boerhaave's syndromes. And ponder, briefly, the mortifying impact of sustained laughter on the urinary tract (detailed in a 1982 Lancet paper titled "Giggle Incontinence").
The new analysis, "Laughter and MIRTH (Methodical Investigation of Risibility, Therapeutic and Harmful)," was drawn from about 5,000 studies. It appears in BMJ, formerly known as The British Medical Journal, which has long featured rigorously researched but lighthearted articles in its Christmas issue. Deputy editor Tony Delamothe said the "MIRTH" study was peer-reviewed -- presumably by a doctor with a carefully managed sense of humor.
Last spring, the "MIRTH" co-authors, consultant physicians Robin E. Ferner, a University of Birmingham honorary professor of clinical pharmacology, and Jeffrey K. Aronson, an Oxford fellow in clinical pharmacology, who study medicines' benefits and harms, discussed what benefit-harm they could explore to win a coveted BMJ Christmas issue berth. Dr. Delamothe said BMJ gets nearly 120 submissions and accepts about 30.
Drs. Ferner and Aronson considered holiday foods, but their tastes were not in concert. "He likes sweet wines, and I like dry wines," Dr. Ferner explained. Then they found common cause: "But we both like dry humor."
They winnowed the papers that mentioned laughter to 785, putting them in three categories: benefits (85), harms (114) and conditions causing pathological laughter (586).
The question was timely, they argued, because BMJ had not addressed laughter in a serious way in more than a century. In 1898, it published a case study of heart failure in a 13-year-old girl after prolonged laughter.
And a 1997 discussion of Boerhaave's syndrome -- a spontaneous perforation of the esophagus, a rare though potentially lethal event -- mentioned that one unusual cause is laughter.
Then there is the mysterious Pilgaard-Dahl syndrome, identified in a 2010 article as a pneumothorax (air or gas abnormally collecting between the lung and chest wall) in middle-aged male smokers that was induced by laughter. It takes its name from Ulf Pilgaard and Lisbet Dahl, Danish revue performers.
There were other respiratory threats occasioned by laughter, Dr. Ferner said. The popping of alveoli (air sacs in the lungs, which together typically contain about 600 million): "If you're going to make asthmatics laugh heartily," Dr. Ferner said, "they might want to have an inhaler by their side." (This, extrapolated from a 1936 experiment on the mechanism of laughter in asthmatics.)
There are choking hazards, such as ingesting food during belly laughs.
The MIRTH review did take an evenhanded, cost-benefit approach to laughter, noting ample evidence of its salutary effects. It concluded that laughter's benefits included reduced anger, anxiety and stress, lower cardiovascular tension, blood glucose concentration and risk of myocardial infarction. "The benefit-harm balance," the authors wrote, "is probably favorable."
Recent studies have found that laughter "reduces arterial wall stiffness" and "improves endothelial function." A 2008 study of chronic obstructive pulmonary disease patients concluded that laughter inspired by Pello the clown improved lung function.
Medical clowning has been observed and embraced. But one study left Dr. Ferner almost speechless. A 2011 fertility study reported that when a clown dressed as a chef de cuisine entertained would-be mothers for 12 to 15 minutes after in vitro fertilization and embryo transfers, the pregnancy rate was 36 percent, compared with 20 percent among an unentertained control group. "Why a chef de cuisine?" Dr. Ferner asked plaintively.
Despite a comprehensive medical literature review of laughter, Dr. Ferner saw still-uncharted territory. "We don't know how much laughter is safe. There's probably a U-shaped curve: Laughter is good for you, but enormous amounts are bad, perhaps," he said. "It's not a problem in England."