The team studied a 1952 edition of the Baseball Register, which allowed them to study pictures of players from that year and then check up on the age at which they died. The researchers found that the broadness of the player’s smiles and the extent of the creases around their eyes whilst they were smiling, was directly relational to the age to which they went on to live to.

Although the reports I have read give no indication as to why this relationship between smiling and longevity seems to hold, it’s fair to assume that the players with the broad smiles were genuinely more relaxed and happy people, thus less prone to die from stress related illnesses later on.

Source : Broader Smile, Longer Life : Study