Excerpt from: About.com (click for full article)
Studies published in Nature describe data that seem to point to a link between sodium and the risk for developing autoimmune diseases, such as multiple sclerosis.
The researchers found that people who ate fast food more than once a week had a higher number of TH17 cells than people who did not eat fast food. These TH17 cells usually help the body repair itself or fight disease, but it seems like salt may cause them to multiply too fast, at which point they attack the body's own tissues and cause autoimmune disease.
Exposing the immune cells of mice to sodium caused the cells to produce more TH17. When mice that were genetically engineered to develop MS were fed a high-salt diet, their disease progressed rapidly.