Every fast food restaurant pours it into their nuggets, chips and fries. Snack foods overflow with it. And now researchers think it’s killing us with an epidemic of autoimmune diseases like arthritis, multiple sclerosis, lupus, diabetes and thyroid dysfunction.

According to a study at Yale and Harvard, our danger comes from an overabundance of salt hidden in our processed food.

They found that adding salt to the diet of laboratory animals induced production of a type of T cell previously associated with autoimmune diseases and that animals on salt diets developed a more severe form of multiple sclerosis called experimental autoimmune encephalomyelitis.

The research expands the understanding of how one type of immune cell, the T helper 17 or Th17 cell, develops, and how its growth influences the development of other kinds of immune cells.

“The question we wanted to pursue was: How does this highly pathogenic, pro-inflammatory T cell develop?” says researcher Vijay Kuchroo. “Once we have a more nuanced understanding of the development of the pathogenic Th17 cells, we may be able to pursue ways to regulate them or their function.”

“Humans were genetically selected for conditions in sub-Saharan Africa, where there was no salt,” adds researcher David Hafler. “Today, Western diets all have high salt content and that has led to increase in hypertension and perhaps autoimmune disease as well.”