By Alice G. Walton
Doctors and researchers have been recommending eating less salt for a long time, largely for cardiovascular reasons. Now three new studies suggest that in addition to raising our risk for high blood pressure, heart disease, and stroke, too much salt in the diet may trigger autoimmune diseases like multiple sclerosis (MS) and rheumatoid arthritis.
The finding adds fuel to the idea that our environments, including what we put in our bodies, can matter as much as our genes when it comes to disease risk.
The connection between salt and autoimmune diseases was discovered somewhat by accident. Researchers noticed a link between eating at fast food restaurants and the production of inflammatory cells. Under normal conditions inflammation is part of the body’s response to foreign invaders like viruses and bacteria, but in autoimmune diseases, the immune system attacks the body’s own healthy tissue.
Researchers found that adding salt to the diets of mice produced an enzyme that triggers the production of T cells, a type of immune cell that has been linked to autoimmune diseases. Mice fed high-salt diets also developed a particularly severe type of MS, called experimental autoimmune encephalomyelitis.
There has been a steady increase in the prevalence of autoimmune diseases like MS and type 1 diabetes in recent decades, which suggests that something in the environment may be acting as a trigger. Salt is certainly not the only environmental trigger for MS and other autoimmune diseases, but it may be one piece of the puzzle, and will be studied more in the future.
One of the reasons that the link was not discovered sooner is that most test tube experiments are done using the concentrations of salt found in the blood, not the tissues where immune cells are active.
"We may have been using the wrong concentrations of salt in our experiments for the past half-century," said one of the studies’ authors, David Hafler, in a statement. "Nature did not want immune cells to become turned on in the pipeline, so perhaps blood salt levels are inhibitory."
The current experiments were performed in rodents, not humans, and clinical trials will be on the way soon. But Hafler isn’t waiting around to make recommendations to his own patients with autoimmune diseases: "I already recommend that my patients use a low-salt, low-fat diet.” It’s always a good idea to talk to your doctor before making any significant changes to the diet, but most doctors agree that a low-sodium diet is the way to go.
Hafler is a researcher and professor at Yale University; the three papers were published in the journal, Nature.
March 26, 2013