Cardiac surgeon Dr. Gulshan Sethi is unfazed by the scowly-faced skeptics who show up to his laughter yoga sessions, arms folded across their chests.

The way he sees it, those are the people most in need of a good belly chuckle. His yoga sessions include stretching, breathing, chanting, clapping and simulated laughter that often turns into the real thing.

Laughter activates the body’s natural relaxation response, explains Sethi, 73, who is head of cardiothoracic surgery at Tucson Medical Center. It’s like internal jogging, providing a good massage to all internal organs while also toning abdominal muscles, he says.

Frowning is often triggered by stress, which Sethi says is either the primary or aggravating cause of most diseases. His comments are not anecdotal — Sethi is a purveyor of evidence-based medicine.

He’s on the faculty at the University of Arizona’s Center for Integrative Medicine, where he first discovered the benefits of laughter yoga. That was eight years ago, when he did a fellowship at the center and simultaneously discovered the writings of journalist and author Norman Cousins.

In his 1979 book, “Anatomy of an Illness,” which describes the power of humor in healing the body, Cousins writes how a good 10-minute laugh has an anesthetic effect on pain.

Sethi used laughter yoga to help his own back pain as an alternative to taking prescription drugs. He cites evidence that laughter increases the body’s levels of endorphins, which are natural painkillers. Increasing endorphins also improves one’s overall sense of well-being, he notes.

Spend any time around Sethi and there’s a good chance of catching him demonstrating one of his laughter yoga exercises — clapping his hands and chanting ha ha, ho ho ho. When they spot him walking through the Tucson Medical Center hallways, staff and volunteers who have been in his sessions often do the exercises, too.

“We smile and laugh. To me it is a coping skill, and a joyful experience,” Sethi said. “When you laugh together there is so much happiness.”

Tucson Medical Center volunteer Ginny Robbins, has been to two of Sethi’s laughter yoga sessions, which he gives periodically in the community. Most recently he led a class at The Core, which is the hospital’s wellness center located at the La Encantada shopping center on Tucson’s north side. His former heart patients are often among those in attendance.

Robbins continues to use a trick she learned in Sethi’s class, where she’ll answer an imaginary phone call when she’s irritated and pretend there’s a person on the other end telling her a very funny joke.

“It’s usually when I am in the car getting annoyed about traffic,” she said.

Tucson business owner David Smith found Sethi’s recent class at The Core, “fun, light and factual.”

He particularly liked one of Sethi’s exercises where the Indian-born surgeon pretends to be making a mango lassi, then asks the class to join in.

“He was pouring it back and forth to aerate it and make it bubbly, and then it makes you laugh,” Smith said. “Of course laughter is good stuff. I don’t know how people are grouchy all the time.”

Indeed, there are people who need more laughter in their lives. The way Sethi explains it, children laugh 300 to 400 times per day because it is their nature to be joyful. But adults laugh just 12 to 15 times per day, he says.

Some other compelling evidence he’s found through research — laughter increases heart rate variability, which is related to good health.

“In the 13th Century surgeons used laughter to distract patients from pain,” Sethi said. “It is good for cancer patients. It increases immunity and overall well-being.”

He stresses that laughter is a complementary therapy and not meant to replace medical treatments for disease.

And it’s a complementary therapy that certainly can’t hurt, said Smith, the local business owner. It doesn’t carry the dangers of prescription drugs, for example.

“I’ve never heard of laughter yoga killing anyone,” he said. “What do you have to lose?”

Contact health reporter Stephanie Innes at sinnes@tucson.com or 573-4134.