@ Slaney Thanks for the links. As you rightly point out, the Handbook you reference has had positive reviews, although with some critical caveats.
Bottom line- most of the studies in this area have been, by objective standards, poor.Too often, data has been taken from studies designed to look for something else, and presented as a form of proof.Other studies have been too small, or poorly controlled, or show clear evidence of bias.
The take home message from some of the better studies is that social factors can influence your health. If you are socially isolated, or permanently stressed for whatever reason, it could have an impact on both your quality of life and your longevity.
If you are an active member of a social group, have a sensible diet,enjoy moderate exercise, refrain from smoking and drink alcohol in moderation then I suspect you would see little if any difference in qualitative or quantitative measures of happiness and longevity between atheists and theists.