A positive link between laughter and healthy function of blood vessels was first reported in 2005 by researchers at the University of Maryland Medical Center with laughter causing the inner lining of blood vessels, the endothelium,
to dilate or expand such to increase blood flow. Drs. Michael Miller
(University of Maryland) and William Fry (Stanford), theorize that
beta-endorphin like compounds released by the hypothalamus activate
receptors on the endothelial surface to release nitric oxide, thereby
resulting in dilation of vessels. Other cardio protective properties of
nitric oxide include reduction of inflammation and decreased platelet
aggregation. The association between laughter and endothelial dilation
was recently confirmed by other investigators.
Laughter can also be brought on by tickling.
Although it is found unpleasant by most people, being tickled often
causes heavy laughter which is thought to be a reflex of the body, and
is often uncontrollable.
It
has also been shown that laughter is highly contagious, as shown in one
case where schools in an area were closed for six months as a result of
a massive laughter epidemic.
