Medicinal mirth gets research rebuke.

The belief that laughing and humor promote physical health is widespread. A growing movement among health-care workers touts "therapeutic humor" through seminars, workshops, videotapes, and Web sites. However, results of research on the purported health benefits of mirth call to mind a well-told joke with a punch line that falls flat. Or so concludes psychologist Rod A. Martin of the University of Western Ontario in London, Ontario.

"Despite the popularity of the idea that humor and laughter have significant health benefits, the current empirical evidence is generally weak and inconclusive," Martin says.

Martin's review of 41 scientific articles, published since 1960, that relate humor or laughter to various aspects of physical health appears in the July PSYCHOLOGICAL BULLETIN.

Several experiments have found signs that watching funny videos bolsters people's immune systems. However, other comedy-exposure studies found either no changes or even declines in immune system function. Scientists have yet to establish whether any component of immunity corresponds to how much a person laughs at funny material, Martin says.

Evidence that watching humorous videotapes boosts pain tolerance is also ambiguous, he remarks. Comparable rises in pain tolerance occurred in a few studies in which people watched sad or disgusting videotapes, suggesting that various emotional states take some of the sting out of physical hurts.

People with a good sense of humor, as measured on questionnaires, have yet to display any marked advantages in immunity, pain resistance, or susceptibility to physical illness over those with weaker funny bones, Martin notes. Published reports provide little support for the theory that a sense of humor diminishes daily stress levels and none for the notion that it adds years to one's life, he adds.

Not that humor and laughing aren't worthwhile. People who make others laugh may make friends especially easily, Martin theorizes. If so, they probably reap the well-established health benefits of having many supportive relationships. Also, certain humor styles, such as self-deprecation, possibly improve relationships and physical health over time, while other approaches, such as sarcasm, may do the opposite.