I've always thought that smiling was contagious. When someone smiles at you on the street, you can't help but smile back. It's amazing how little things seem to make the day that much brighter. Smiling is considered an important indicator of positive emotion and confidence. It has also been said that smiling can make stressful situations more tolerable. A new study by the University of Kansas reveals that if you smile at someone, not only are you brightening up their day, you are also benefiting your own health. It was found that smiling can have positive effects on the heart. Those who smiled during stressful situations had a lower heart rate and recovered faster, bringing new meaning to the saying "grin and bear it". So cheerful people might just be onto something. It's perhaps an especially timely study for Hong Kong, a city where nearly one in six people suffers from anxiety or depression, according to the interim government report, the Hong Kong Mental Morbidity Survey 2010-13. Major depressive disorders will become the second-biggest contributor to the global burden of disease by 2020, according to the World Health Organisation. Previous studies have shown more than 300,000 Hongkongers suffer from depression, and three times more women than men. Based on projections from the latest population figures, about 700,000 middle-aged women in Hong Kong are at high risk of developing depression. The University of Kansas study is the first of its kind to examine the effects that smiling has on the body while under stress. "We wanted to scientifically examine if smiling through a stressful situation could actually have physiological benefits," says researcher Tara Kraft. Her team recruited 169 subjects from Midwestern University - all healthy 18-to-25-year-old men and women. They were screened for any facial muscular disorder prior to testing and then randomly assigned to one of three groups: neutral expression control, standard smiling and Duchenne smiling group. A standard smile uses muscles around the mouth whereas a Duchenne smile is when the muscles around the mouth and eyes are engaged. The participants were told they were being tested on their ability to multitask so as to prevent awareness or reaction to smiling. They were also all previously taught the correct smiling method. The subjects were put through a stressful situation. They were asked to complete a two-minute mirror star-tracing task: place their non-dominant hand inside a box and repeatedly trace a star by looking at a reflection of the star in a mirror. They were asked to be as accurate with their drawings as possible, while being given incorrect information regarding performance. They were also told they would be rewarded with chocolate if they managed to reach the unattainable goal that was set. After this, participants had a five-minute rest and were then asked to submerge their hand in iced water for one minute before having another five-minute rest and repeating the process. Throughout the exercises the participants were asked to produce a Duchenne smile, a standard smile or remain neutral. The subjects were tested to see how their hearts handled the stress. When we are stressed, our heart beats faster, as part of our "fight or flight" instincts. Those who were smiling had a slower heart rate and a faster recovery rate than those who had a neutral expression. But the difference between those who had a Duchenne smile and a standard smile was not significant. Although smiling is not considered the same as happiness, it is an indicator. It is often thought that facial expressions are a consequence of emotions felt by an individual. But according to the self-perception theory by social psychologist and professor emeritus at Cornell University, Daniel Bem, if a person acts happy they will become happy. Kraft says the results of the study were what the team had expected: that smiling is good for your health because it reduces the harmful effects of stress on the heart. "Between the participants and researchers, we were smiling through the entire process," he says. If only everything in life could be cured with a smile.