This article discusses a recent paper which summarizes a ton of papers that find a positive correlation between happiness and longevity. It also concluded that anxiety, depression, and pessimism were linked to higher rates of disease and a shorter lifespan. Interesting correlations except that the lead author of the paper makes a causal connection (happiness etc causes greater longevity) which doesn't follow for reasons that are all too familiar.
Of course its plausible that being a happy dude makes you live longer but it's also plausible that not expecting to live long is a bit of a downer. I, for one, am delirious that I am going to outlive you all. Alternatively, you could have "the right stuff" which makes you both happy and healthy.