Diets High in Salt May Trigger Multiple Sclerosis

By Mollie Bloudoff-Indelicato, Everyday Health Staff Writer

High-salt diets could speed the onset and progression of autoimmune diseases like multiple sclerosis and rheumatoid arthritis in individuals already genetically predisposed to develop such conditions, according to a study published in the journal Nature.
Scientists at the Yale Medical School and MIT, among others, say that the average American diet, high in sodium, could trigger multiple sclerosis (MS), an autoimmune disease that affects an estimated 2.1 million individuals worldwide. MS patients have aggressive white blood cells that attack healthy tissue, destroying the pathways that relay information throughout the body. Salt may increase production of these aggressive cells, possibly aggravating symptoms, according to the study authors.
"The salt could be one environmental risk factor which could lead to the outbreak of MS because it leads to an increase of these aggressive cells," says Markus Kleinewietfeld, MD, an immunologist at the Yale University Medical Center and lead author of the study.
Researchers injected 40 millimolars of sodium chloride into mice bred with the animal version of multiple sclerosis. This prompted the aggressive cells, also known as T17 cells, to almost double in number, Dr. Kleinewietfeld says. The rapid increase caused mice to develop MS symptoms faster and more severe than controls, he adds.
The prevalence of autoimmune diseases has increased substantially over the past 50 years, an uptick Kleinewietfeld attributes, in part, to the Western appetite for fast food and prepackaged meals, which are high in salt. Doctors caution consumers against consuming too much salt, due to its role in elevating blood pressure, but until now, there was no known link to MS.
These findings could result in medications designed to reduce the severity of multiple sclerosis symptoms. They also hold implications for post-surgery problems like graft-versus-host disease, in which the immune system rejects a transplanted organ. Patients adhering to a low-salt diet might not see such a strong response, thus reducing the risk of organ-transplant fatalities.
While there is significant evidence linking salt to a heightened autoimmune response, the Yale study does not distinguish between acceptable degrees of salt intake and harmful degrees. Sometimes doctors want to boost the immune system, and salt in low doses — like the amount found in chicken noodle soup — can help the body fight off sickness, says David Hafler, MD, a neurologist at the Yale School of Medicine and co-author of the study. Figuring out where to draw the line is difficult, he adds.
Salt is also not the only environmental factor thought to trigger MS. While scientists have identified more than 100 genetic variants that cause MS, they have yet to definitively pinpoint exact disease activators. Cigarette smoke and vitamin D deficiency are also possible antagonists. More likely, Dr. Hafler says, it’s a combination of many things.
“What we can say is that it’s a complex genetic disease,” Hafler adds. “It’s not bad genes but a bad interaction between genes and the environment. I would be shocked if salt was the only factor; I suspect that there are multiple factors involved.”
The next step is to expand the salt-MS research to include humans. Researchers plan on tracking patients on low-salt diets to determine whether the reduction will alter T-17 cell production. Kleinewietfeld suggests that future findings can be used to both decrease and increase immune system response — depending on the patient’s requirements.
“One really could think about different applications,” he says. “This is the beginning. We’re starting to explore this.”