Shared laughter is a hallmark of a relationship with staying power, according to new research from the University of North Carolina at Chapel Hill.

The researchers found that laughing together is a useful objective marker of relationship's well being, according to the study, which was published in the journal Personal Relationships.

They video-recorded 71 heterosexual romantic couples recounting the tale of how they first met, looking specifically for moments of shared laughter. They counted both the frequency and duration of that simultaneous laughter, concluding it was "uniquely positively associated with global evaluations of relationships quality, closeness and social support," according to the study.

“We can all think of a time when we were laughing and the person next to us just sat there totally silent,” lead researcher Laura E. Kurtz, a social psychologist in the Department of Psychology there, told Time. “All of a sudden that one moment takes a nosedive. We wonder why the other person isn’t laughing, what’s wrong with them or maybe what’s wrong with us and what might that mean for our relationship.”

In her interview with Time, Kurtz pointed out some differences between the sexes when it came to happy outbursts. “Women laughed more than males. And men’s laughs are more contagious: When men laugh, they are 1.73 times more likely to make their partner laugh.”

While laughter and relationship quality have not been particularly well researched, this study adds to what is known about laughter and well being. For example, Today Health and Wellness lists having fun together as one of five ways to strengthen a marriage, along with sharing housework, saying "I love you," finding time to get away alone together and holding hands publicly.

The documented benefits of laughter are more diverse than strengthening a couple's bonds. Half a decade ago, the University of Maryland introduced a study showing that "laughter is the best medicine" is much more than a catchy phrase. It's good for the heart. Physically.

In background material, those researchers explained that they looked at how 300 people respond to situations with — or without — humor. Half had heart disease and had either had a heart attack or had undergone a heart-bypass operation. The other half had healthy hearts. A series of multiple-choice questions looked at how much and when people laughed, while a true-false series measured anger and hostility.

Those with heart disease demonstrated significantly less humor and more anger and hostility, the study found.

A study from the United Kingdom published in Proceedings of the Royal Society found a link between social laughter and the ability to handle pain. The researchers used six experiments, half involving watching videos and the other half involving watching plays, to determine that when someone laughed, his or her pain threshold increased.

Wrote the authors: "The results show that pain thresholds are significantly higher after laughter than in the control condition. This pain-tolerance effect is due to laughter itself and not simply due to a change in positive affect."

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