Yesterday's issue of Nature carries an essay on the question of why intelligent people live longer. Apparently, the correlation is stronger than that between mortality and BMI or blood pressure. I'm not surprised that the correlation is there, but maybe a bit surprised that it is so strong. After all it might be offset by really bright people getting so depressed over the stupid ways of the world that they commit suicide at an early age.
The author seems to think this correlation is a mystery, but I suspect that may be related to the fact that his job depends on research in this area, and if there's no mystery, there are no research grants. I think that even a combination of two of the 4 possible reasons he mentions will be sufficient to explain the effect, namely stupid people doing stupid things (reason 2, paraphrased slightly) and intelligent people getting higher education levels and thus healthier work environments (1). If on top of that, one adds a bit of his reason 4, namely intelligence being an indicator of general "system integrity", i.e. the wiring of the body during development has worked well, I think there isn't anything left to explain.
Oh, and I just had an idea that isn't mentioned in his essay -- maybe the view often found in traditional societies that the elders of a tribe, village, population are the "wise ones" reflects not just their experience but also their higher than average intelligence, in which case the phenomenon isn't a product of modern life styles (reason 1), which leaves 2 and 4.