After you get beyond a fairly low per capita income, one of the biggest known factors on life expectancy is how little income disparity there is. The US, of course, has made a religion out of the value of allowing huge disparities to thrive...
Random link from Google on this.
[link|http://depts.washington.edu/eqhlth/|http://depts.washington.edu/eqhlth/]
Cheers,
Ben