U.S. life expectancy varies by more than 20 years from county to county
Not only county-to-county.  My friend did his PhD dissertation on how (at least in Rochester, NY), life expectancy varies by decades between <i>zip codes</i>.  His research focused on urban Food Deserts and studied how the lack of access to healthy food nearby restricted diets to that available in convenience stores (chips, soda, etc).  I wish I had access to his dissertation, but he just defended a month ago and cannot find it in any publications right now.<p>EDIT:  Not my friend's paper, but here is a similar study: <a href="https://hrs.isr.umich.edu/publications/biblio/8355" rel="nofollow">https://hrs.isr.umich.edu/publications/biblio/8355</a>