Co-author Prof Sir Richard Peto, from the University of Oxford, said light smokers had double the risk of an early death and regular smokers had three times the risk of dying during the study period, but that happiness was "irrelevant".
He said it could have indirect effects if people started consuming large amounts of alcohol or massively overeating, but happiness itself "does not have any material, direct, effect on mortality".
But he warned the myth may be too entrenched to shake off: "People will still believe stress causes heart attacks after this story has been and gone.
"It isn't true, but it suits people to believe it."
In a commentary, Dr Philipe de Souto Barreto and professor Yves Rolland from the University Hospital of Toulouse in France, said: "Further research from a lifecourse perspective is needed since happiness during critical periods, such as childhood, could have important consequences on health in adulthood.