The broader your smile and the deeper the creases around your eyes when you grin, the longer you are likely to live, according to a study published in Psychological Science this week.
Researchers led by Ernest Abel of Wayne State University in Michigan studied 230 photographs of US major league baseball players who started playing before 1950 and grouped them according to their smiles.
The players were rated as "no smile" if they were just looking deadpan at the camera; as "partial smile" if only the muscles around the mouth were involved in their grin; or as "full smile" if the mouth and eyes were smiling and the cheeks were both raised.
The players' pictures were taken from the 1952 Baseball Register, a listing of professionals that is packed with statistics such as year of birth, body mass index, marital status and career length, which reflects physical fitness.
The wealth of statistics allowed the researchers to control for other factors that could affect lifespan.
Of the players who had died as of June 1 last year, those in the no-smile category lived for an average of 72.9 years, those with partial smiles -- just the mouth involved -- died at age 75, while the full-smile players lived to the ripe old age of 79.9 on average, the study showed.
"To the extent that smile intensity reflects an underlying emotional disposition, the results of this study are congruent with those of other studies demonstrating that emotions have a positive relationship with mental health, physical health and longevity," the study says.
It was unclear, the authors said, if the baseball players had smiled spontaneously or if their grins were produced under orders from a photographer.
But, in any case, far fewer individuals had full smiles -- 23 -- than partial or no smiles (64 and 63 respectively), which indicated to the researchers that even if smiles were produced on request, their intensity reflected the player's "general underlying disposition."
So the conclusion could be, if you want to live a long, happy life: hit the books, hit the ball and grin in a way that gives you crow's feet.