Epidemiologists are concerned with uncovering the factors in populations that determine who gets sick, who stays healthy, who lives, and who dies. Human life is inherently social, and looking toward our societies and geography can help explain who is healthy or sick, and why.

“Location, location, location” is a mantra that rings true with respect to life expectancy.
  http://blogs.plos.org/publichealth/2013/02/19/what-determines-health