Walking 30 min/day adds 1.3 years to your life (source: http://walking.about.com/od/healthbenefits/a/livelonger1105....). Moderate obesity takes 3 years from your life (source: http://www.sciencedaily.com/releases/2009/03/090319224823.ht...).
But obviously, none of these factors affect average national life expectancy. Only health care does.