Psychological scientists Tara Kraft and Sarah Pressman of the University of Kansas conducted a series of experiments involving 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.
For the testing phase, participants were asked to work on multitasking activities. What the participants didn't know was that the multitasking activities were designed to be stressful.
Compared to participants who held neutral facial expressions, the study participants who were instructed to smile had lower heart rate levels after recovery from the stressful activities.
"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," Pressman said in a statement. "Not only will it help you 'grin and bear it' psychologically, but it might actually help your heart health as well!"
The findings were published in Psychological Science.