An estimated one in 20 people in the United States have some form of autoimmune disease, conditions in which the immune system, ordinarily the body’s defense against infectious agents, turns on itself, attacking healthy tissue as though it were tumor or other harmful cells. That number is going up year after year. It’s not always clear why this happens, but new research points to salt as a possible factor in a broad spectrum of autoimmune conditions.
Researchers at Yale University put laboratory mice on a high-salt diet and found that they increased production of a type of T cells, the foot soldiers of the immune response, called Th17. Th17 cells are characteristic of autoimmune diseases. The mice developed a condition analogous to multiple sclerosis in humans. Follow-up studies in Boston found that an enzyme that is part of the body’s system for processing salt also activates the production of Th17.
Autoimmune diseases occur when Th17 cells mistake the body’s own organs for invaders. Common autoimmune conditions include type 1 diabetes, Guillain–Barré syndrome, multiple sclerosis, lupus, rheumatoid arthritis, Sjögren’s syndrome, and some kinds of hepatitis. Most of these conditions are partly heritable, but not everyone who is genetically predisposed to an autoimmune condition exhibits one. These discoveries about salt may help explain why. The researchers note that autoimmunity is not wholly genetic, nor wholly environmental; it’s a combination of both. People who, as a result of genetic inheritance, are prone to a type of autoimmune disease, only actually exhibit it when excessive salt in the diet triggers the immune cell production.
It is not yet known whether the salt and autoimmunity connection works the same way in humans as it does in mice, though the same signaling pathways may be involved, and most people probably ought to be watching their salt intake on general principles. There are a number of environmental factors that appear to be linked with autoimmune disorders; one of the most widely known and accepted is the “hygiene hypothesis” that postulates that clean surroundings cause the immune system, deprived of infections to combat, to turn on the body. Salt’s effect on the immune cells themselves may well also be a part of it.