While laughter has long been believed to benefit overall health, new research from Loma Linda University in California identifies many of the physical functions improved by a heartfelt howl.

Lee S. Berk, a preventive care specialist and psychoneuroimmunology researcher at the university's Schools of Allied Health and Medicine, where he also serves as director of the molecular research lab, joined with colleagues in studying the human body's response to mirthful laughter and found laughter helps optimize an array of bodily systems, that include maintaining hormones in the endocrine system, which help with stress reduction.

The researchers also discovered laughter positively affects the immune system; among other impacts, the laughing process increases the production of antibodies and activation of the body's protective cells, which attack cancer cells.

Berk's work, presented at the 2010 Experimental Biology conference in Anaheim, Calif., which wrapped up April 28, demonstrates repetitious "mirthful laughter," coined by the researchers as "Laughercise," prompts one's body to respond in a way similar to the way it would to moderate physical exercise.

Joyous laughing enhances a person's mood, decreases stress hormones, boosts immune activity, lowers bad cholesterol and systolic blood pressure, and even raises good cholesterol, the research says.

"We are finally starting to realize that our everyday behaviors and emotions are modulating our bodies in many ways," said Berk, whose three-week study focused on 14 healthy volunteers, who were tracked to examine the effects that eustress, or, mirthful laughter, and distress have on modulating the key hormones that control appetite.

For the study, each subject was required to watch one 20-minute video at random that was either upsetting or humorous in nature. After waiting one week, each subject was shown another video designed to elicit a reaction opposite to the one encouraged by the first viewing.

For the distressing video clip, the researchers had the volunteer subjects watch the tense first 20 minutes of the movie "Saving Private Ryan," known to distress viewers substantially and equally.

For the eustress video, volunteers got to choose a 20-minute video clip from a variety of humorous options, including stand-up comedians and movie comedies.

The researchers measured each subject's blood pressure and took blood samples immediately before and after watching the videos. Then, the blood samples were separated out into their individual components, with the levels of the hormones involved in appetite measured in the liquid serum during each step of the experiment process.

When the pre- and post-viewing hormone levels were analyzed, it was found those who watched the distressing video showed no statistically significant change in their appetite hormone levels during the 20-minutes they spent watching the video.

On the hand, the subjects who watched the humorous video experienced notable changes in blood pressure and appetite hormone levels.

Berk said the research did not conclude humor increases appetite, but, rather, "laughter causes a wide variety of modulation and that the body's response to repetitive laughter is similar to the effect of repetitive exercise. The value of the research is that it may provide for those who are health care providers with new insights and understandings, and thus further potential options for patients who cannot use physical activity to normalize or enhance their appetite."

While it may seem unimaginable to laugh during bouts of deep depression or intense chronic pain, the process could nonetheless offer a starting point for patients working to regain their appetites and, consequently, improve and enhance their recoveries, Berk said.

The new research expands the role of laughter on the human body and an individual's overall sense of well-being, said Berk, but it further complicates an already-complicated emotion.

"I am more amazed by the interrelatedness of laughter and body responses with the more evidence and knowledge we collect. It's fascinating that positive emotions resulting from behaviors such as music playing or singing, and now mirthful laughter, translate into so many types of [biological] mechanism optimizations," Berk said.

"As the old biblical wisdom states, it may indeed be true that laughter is a good medicine."