This information is old now as it was published in August, 2012 but it bears repeating here.
Researchers at the University of Kansas discovered that smiling during stressful experiences reduces the body's response to stress and might also help the heart.
The smile can be a standard smile (only the mouth is in a smile) or a full-face smile (mouth and eyes engaged in the smile). The researchers found that even though the smile is forced during a stressful event, the recovery rate of the heart is lower than test subjects who used a neutral expression.
So perhaps there is something to be said for us to grin and bear it.
Time to get back to work. I'll put a genuine smile on my face.