New Delhi : Doctors have been advising the high blood pressure patients for ages to cut down intake of salt, but three new studies say high consumption of salt in food may increase the risk of many autoimmune diseases as well, such as rheumatoid arthritis, inflammatory bowel disease and multiple sclerosis (MS).
The studies led by an Indian neurologist, an Israeli biologist, and an American immunologist – all in the US – that appeared on Thursday in the journal Nature gives the first scientific evidence to associate high salt intake with autoimmune diseases. The rigour and the complementary features of the three studies and the relative ease of asking patients with autoimmune diseases to restrict their salt intake seem to warrant quick human trials.
The scientists caution that their results are based on studies on mice and human cells in laboratories, but their findings are significant enough to justify human clinical studies to evaluate the role of salt as a risk factor in autoimmune diseases — conditions in which the immune system turns on and hurts the body”s own organs and tissues.
“The role of high salt diet in autoimmunity in humans has not been tested yet,” said Vijay Kuchroo, professor of neurology at the Harvard Medical School, and principal investigator of one of the studies, while stressing that “these studies lead to a nice hypothesis that could be tested in humans.”
Kuchroo, who graduated in veterinary medicine from Hisar in Haryana and got a PhD in pathology from Australia, before moving to Harvard to pursue neurology, and his collaborators set out to decipher the molecular circuitry involved in the development of a set of white blood cells called Th17 cells that promote inflammation and protect the body from microbes.
But Th17 cells have also been implicated in several autoimmune diseases including ankylosing spondylitis, rheumatoid arthritis, the skin disorder called psoriasis, and the neurological disorder called multiple sclerosis.
The researchers took 18 snapshots of Th17 cells to identify major hubs and nodes involved in their development and spotted a key enzyme that controls the uptake of salt by these cells. They, then, studied the effect of high salt on Th17 and observed that extra salt enhanced the development of disease-causing Th17 cells and exacerbated autoimmunity in mice.
In two studies, Kuchroo, collaborating with Israeli biologist Aviv Regev at the Massachusetts Institute of Technology, and Hongkun Park, a chemist at Harvard University, worked with mouse cells and mouse models of autoimmune disease. “We wanted to understand how the body gets the right kind of immune cells in the right amount, and how it keeps those cells at the right activity level,” said Regev, an associate professor at MIT and scientist at the Broad Institute.
In the third study, David Hafler, an American immunologist at Yale University and his colleagues independently demonstrated through studies on human cells that high salt can drive autoimmune diseases through Th17 cells.
Hafler and his colleagues are in the process of seeking institutional approval to try a low salt diet in a number of acute clinical situations of inflammation. “If one weighs the potential benefit versus risk, it is hard to argue against a low salt diet, particularly in the context of measuring circulating Th17 cells,” Hafler said.
“Salt could be one more thing on a list of predisposing environmental factors that promote the autoimmunity. We suspect other factors such as infection, smoking, and lack of sunlight and vitamin D may also play a role,” Kuchroo said.
The incidence of autoimmune diseases varies — from 1 to 20 cases of inflammatory bowel disease per 100,000 persons per year, about 40 cases of rheumatoid arthritis per 100,000 persons year year, and 1 to 14 cases of ankylosing spondylitis per 100,000 persons.
Autoimmune diseases are currently treated through drugs that alleviate symptoms or suppress the components of the immune system causing the diseases. There are treatments, but no cure, but evaluating the effect of salt restriction should be easy, scientists point out.
They believe the knowledge of the biological hubs and nodes involved in Th17 development may also help them design new drugs for autoimmune disorders. “If we understand the network, we can pinpoint nodes to target,” said Amit Awasthi, a team member who has since moved to the Translational Health Science and Technology Institute in Faridabad in Haryana.
