How about that. I didn't know that smiling was linked to long life.
Here's a recent study that found that smiling, even when it's manufactured, can lower heart rate and blood pressure. (Participants held a pencil in their mouth to unknowingly mimic a smile. Looks like German Chancellor Merkel is working on it.)
Grin and Bear It: The Influence Of Manipulated Facial Expression On The Stress Response, Psychological Science, September 2012
Darwin was one of the first to write about it:
"The free expression by outward signs of an emotion intensifies it. On the other hand, the repression, as far as this is possible, of all outward signs softens our emotions. ... Even the simulation of an emotion tends to arouse it in our minds."
- Charles Darwin, 1872, in Origin of Species, discussing his Facial Feedback Hypothesis