Most people have heard the phrase "laughter is the best medicine," but Air Force Col. Jacqueline Killian has the scientific proof to back it up.

Killian, a senior nurse scientist for the 711th Human Performance Wing, at Wright-Patterson Air Force Base, Ohio, focused her 2015 Ph.D. research at the Uniformed Services University of the Health Sciences in Bethesda, Maryland on using laughter yoga as an intervention to mitigate the effects of stress on students at USU.

Laughter yoga, she said, is not what people may think of when they think of traditional yoga. Laughter yoga, popularized by Dr. Madan Kataria in the 1990s and early 2000s, is a combination of laughter exercises interspersed with pranayama, or the practice of breath control in yoga.

"The yogic aspect doesn't have to do with yoga poses, it has to do with yogic breathing," Killian said.

Killian monitored the students, all military officers, and graduate students from programs throughout USU, before, during, and after the introduction of laughter yoga, and the results spoke, or perhaps laughed, for themselves.

"I asked participants before, at the two-week mark, and one month out about their perceived stress levels and resilience," said Killian. "I also used the Positive and Negative Affect scale and monitored for depression and anxiety."

The Positive and Negative Affect Schedule is one of the most widely used scales to measure mood or emotion. The scale is comprised of 20 items, with 10 items measuring positive affect (e.g., excited, inspired) and 10 items measuring negative affect (e.g., upset, afraid). Each item is rated on a five-point scale, ranging from 1 (very slightly or not at all) to 5 (extremely), to measure the extent to which the affect has been experienced over a specific time.

She also asked the participants open-ended questions to find out what they thought may be changing because of the laughter yoga. That was the most surprising part for her.

"Some of them reported that they were sleeping better, that they were drinking less alcohol or caffeine, or that they were exercising more," Killian said. "Some reported that family members or colleagues even commented about how much better their attitude was or how much happier they seemed. It was almost like participating in the laughter yoga gave them permission to take care of themselves better."

Among the other results the participants reported were decreased stress levels and increased resilience.

"Over time, once we analyzed the data, we found that just participating in laughter yoga four times, twice a week for two weeks, actually did decrease their perceived stress levels and their negative affect, and it improved their resilience scores and their positive affect, said Killian.