Grinning and bearing it gets us through many of life's tricky situations.

But researchers have found smiling really does help reduce stress and boost the health of the heart.

A study from the University of Kansas investigated the potential benefits of smiling by looking at how different types of smiling, and the awareness of smiling, affects a person's ability to recover from episodes of stress.

Study author Tara Kraft said: 'Age old adages, such as 'grin and bear it' have suggested smiling to be not only an important nonverbal indicator of happiness but also wishfully promotes smiling as a panacea for life's stressful events.

'We wanted to examine whether these adages had scientific merit; whether smiling could have real health-relevant benefits.'

The team found smiling could indeed influence our physical state.

Smiles are generally divided into two categories: standard smiles, which use the muscles surrounding the mouth, and genuine or Duchenne smiles, which engage the muscles surrounding both the mouth and eyes.

Previous research shows that positive emotions can help during times of stress and that smiling can affect emotion; however, the work of Kraft and Pressman is the first of its kind to experimentally manipulate the types of smiles people make in order to examine the effects of smiling on stress.

The researchers recruited 169 participants from a Midwestern university. The study involved two phases: training and testing.

During the training phase, participants were divided into three groups, and each group was trained to hold a different facial expression. Participants were instructed to hold chopsticks in their mouths in such a way that they engaged facial muscles used to create a neutral facial expression, a standard smile, or a Duchenne smile.
Chopsticks were essential to the task because they forced people to smile without them being aware that they were doing so: only half of the group members were actually instructed to smile.

For the testing phase, participants were asked to work on multitasking activities, which unknown to them were designed to be stressful.

The first activity required the participants to trace a star with their non-dominant hand by looking at a reflection of the star in a mirror. The second activity required participants to submerge a hand in ice water.

During both of the stressful tasks, participants held the chopsticks in their mouth just as they were taught in training. The researchers measured participants' heart rates and self-reported stress levels throughout the testing phase.

The study found those who were instructed to smile and had Duchenne smiles had lower heart rate levels after the stressful activities compared to participants who held neutral expressions.

Those participants who held chopsticks in a manner that forced them to smile, but were not explicitly told to smile as part of the training, also reported a positive affect, although this wasn't as marked.

These findings show that smiling during brief stressors can help to reduce the intensity of the body's stress response, regardless of whether a person actually feels happy.

'The next time you are stuck in traffic or are experiencing some other type of stress,' says Ms Pressman, 'you might try to hold your face in a smile for a moment. Not only will it help you 'grin and bear it' psychologically, but it might actually help your heart health as well!'

The study is in the journal Psychological Science.