katiesw1/FlickrResearchers found smiling can reduce stress levels and low the heart rate while performing difficult tasks.
Writing in Psychological Science, the authors tell how they studied the effects of different types of smiling in difficult situations.
Tara Kraft, of the University of Kansas, 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."
She and Dr Sarah Pressman divided smiles 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.
Kraft and Pressman worked to manipulate the types of smiles to examine the effects on stress.
They recruited 169 participants from a Midwestern university and divided them into three groups, with each group was trained to hold a different facial expression.
They 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.
Participants were then asked to work on multitasking activities which, unknown to them, were designed to be stressful.
During both of the stressful tasks, participants held the chopsticks in their mouth just as they were taught in training and the researchers measured participants' heart rates and self stress levels.
Compared to participants who held neutral facial expressions, participants who were instructed to smile, and in particular those with Duchenne smiles, had lower heart rate levels after recovery from the stressful activities.
The 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 smaller decrease in positive affect compared to those who held neutral facial expressions.
Dr Pressman said that the 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.
She said: "The next time you are stuck in traffic or are experiencing some other type of stress 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."