"We believe laughing is good for your health,"
said Michael Miller of the University of Maryland
School of Medicine in Baltimore, who led the research.
"And we think we have evidence to show why that's
A growing body of other evidence has suggested
that negative emotions, particularly depression and
stress, can be harmful, making people more prone to
illness, more likely to experience suffering from
their ailments and less likely to recover as quickly,
or at all. One recent study even found sudden emotional
shock can trigger life-threatening heart symptoms
that many doctors mistake for a classic heart attack.
Miller himself, along with his colleagues, had done
a study that found people who have a negative reaction
to social situations tend to be more prone to heart
But far less has been done to examine whether
positive emotions can reduce the risk and complications
"The focus is always on the negative aspects,"
he said. "We thought, 'Why not look at the opposite?'
So they decided to examine the ability of
blood vessels to expand -- known as vasodilation.
Poor vasodilation can increase the risk of heart attacks
and strokes by making the passageways prone to being
blocked, cutting off vital blood flow.
The researchers asked 20 healthy men and women
to watch clips of two movies -- either the violent
opening battle scene in the 1998 film "Saving Private
Ryan" or a humorous scene from a comedy, such as the
The researchers tested the subjects' vasodilation,
before and after the movie, by constricting and releasing
an artery in their arms with a blood pressure cuff
and then using ultrasound to measure how the blood
vessels were functioning.
The researchers discovered striking differences
depending on which movie the volunteers had watched.
Blood flow was significantly reduced in 14 of the
20 volunteers who saw the stressful film. In contrast,
blood flow markedly increased in 19 of the 20 volunteers
after watching the funny movie, the researchers reported
last week at a meeting of the American College of
Cardiology in Orlando.
Overall, blood flow decreased by about 35
percent after experiencing stress but increased 22
percent after laughter -- an improvement equivalent
to that produced by a 15- to 30-minute workout.
"It was a pretty dramatic difference," Miller
Previous research has indicated that stress
hormones may be the primary culprit by which negative
emotions harm health. When a person is under stress,
the body pumps out hormones such as adrenalin and
cortisol. That is designed to prime the body for a
fight or a flight, but the hormones can have detrimental
effects on the body, including suppressing the immune
system and constricting blood vessels.
Miller and his colleagues hypothesize that
laughter may have a contrasting effect, causing the
body to release other natural chemicals known as endorphins
-- pleasure-producing agents best known for producing
the "runner's high" -- that may counteract the effects
of stress hormones and cause blood vessels to dilate.
The researchers acknowledge
they are still a long way from proving their hypothesis
or fully understanding the process, but they say the
theory makes sense.