Scientists have implicated dietary salt in the development of autoimmune diseases, which are caused when the body’s naturally protective immune system attacks and destroys healthy tissues and organs. Some researchers believe the modern diet, including consumption of fast foods, may play a role in the mysterious evolution of these conditions.
Scientists have identified about 100 genetic variants - mutations that shuffle the genetic material of a living cell - that appear to play a role in the development of autoimmune diseases, including the crippling condition known as multiple sclerosis, or MS. Evidence shows that these mutations are not inherited, but instead are triggered by an environmental factor.
A previous infection, vitamin D deficiency, smoking and obesity have been identified as potential triggers. Now, researchers believe dietary salt may also act as a gene-altering trip wire, causing the body’s immune system to begin misdirecting protective T-cells against healthy tissue.
In two papers published this week, researchers at Harvard Medical School and the Broad Institute in Massachusetts describe potential molecular pathways by which salt might induce an autoimmune response.
And in a third paper, researchers at Yale University describe dramatic results when they fed one group of mice a low-salt diet and another group of rodents a diet high in sodium. All of the mice were bred to develop a disease that mimics MS.
David Hafler is head of the Department of Neurology at Yale. Hafler says the rodents that consumed less salt walked normally but with a limp tail.
“Animals on the high salt were basically paralyzed and couldn’t move around the cage," said Hafler. "So, [it was] a very dramatic difference in the extent of the disease.”
Hafler says researchers stumbled upon the possible salt link while studying the variety of bacteria living in the guts of 100 human subjects, noticing that those who ate at fast food restaurants had high levels of inflammatory T cells in their blood. Inflammation is a sign of immune system activation, and autoimmune diseases - including MS, type 1 diabetes, lupus and rheumatoid arthritis - have all been on the rise in recent years. Even rates of heart disease, caused by an inflammatory process, have skyrocketed.
Hafler says the genetic variants that contribute to MS and the other autoimmune disorders are not necessarily bad genes.
"But it's a bad interaction between genes and the environment," he said. "And what the study really has demonstrated is that salt is likely or may be one of the environmental factors that was previously unknown."
All three studies on sodium as a potential trigger of autoimmune disorders are published in the journal Nature.