Compared With Usual Sodium Intake, Low- and Excessive- Sodium Diets AreAssociated With Increased Mortality: A Meta-Analysis

http://m.ajh.oxfordjournals.org/content/early/2014/03/26/ajh.hpu028.1.full.pdf

conclusions

Both low sodium intakes and high sodium intakes are associated with increased mortality, consistent with a U-shaped association between sodium intake and health outcomes.
doi:10.1093/ajh/hpu028