Several teams of scientists have simultaneously published data in the journal Nature suggesting a link.
Salt may activate a part of the immune system which can target the body.
Experts said the findings were very interesting and plausible, but were not a cure for people with MS.
The body’s defence against infection can go horrible awry, turning on the body and leading to autoimmune diseases including Type 1 diabetes, rheumatoid arthritis and multiple sclerosis.
Genetics is thought to increase the risk of such diseases, but the world around us also has a major impact. One of the leading theories behind multiple sclerosis is a viral infection, but smoking and a lack of vitamin D may make the condition more likely.
Now researchers believe they have the first evidence that the amount of salt in our diet may also be contributing.
Teams of researchers at the Brigham and Women’s Hospital and the Broad Institute of MIT and Harvard were investigating a part of the immune system which has been implicated in autoimmune diseases.
They wanted to know how T-helper 17 cells were produced.
A sophisticated analysis of the complicated chemistry needed to form a T-helper 17 cell – which involved carefully monitoring cells and reverse engineering the changes – identified a critical gene. But the gene had been seen before.
“Its day job is to increase salt uptake in the gut,” said Dr Vijay Kuchroo from Brigham and Women’s Hospital. “When we put extra salt in the culture dish it was one of those ‘Aha’ moments, the cells were becoming T-helper 17 cells.”
Mice fed a high-salt diet were more likely to develop a disease similar to MS in experiments.
Meanwhile, researchers at Yale University were also investigating salt and looking at human cells.
David Hafler, professor of immunobiology at Yale, told BBC news online: “In mouse models of MS, those fed high-salt diets had significantly worse disease.
“We were all really quite surprised to see how changes in dietary salt could have such a profound effect.”
There is caution about over-interpreting what is very early research. Studies are now taking place in people with high blood pressure, also caused by high salt intake, to see if there is a link between salt and autoimmune diseases in people.
Dr Aviv Regev, from the Broad Institute, said: “All we can do is bring the current state of knowledge to the public, we have absolutely no recommendations, there’s always a gap between scientific discovery and translation to the clinic.”
Prof Hafler added that a low salt-diet was, however, unlikely to cause harm.
Commenting on the findings, Prof Alastair Compston, from the University of Cambridge, told the BBC the findings were plausible, unexpected and very interesting.
“Like all good science it is introducing a brand new idea that nobody had thought of.”
He said that salt may have a similar effect to other factors such as smoking and sunlight which alter the odds of getting the disease.
However he cautioned: “There is no prospect of a low salt diet curing MS. If you already have the disease and go on a low salt diet the horse has already bolted.”
Dr Susan Kohlhaas, head of biomedical research at the MS Society, said: “This is a really interesting study and it’s positive to see new avenues of MS research being explored in this way.
“It’s still too early, however, to draw firm conclusions on what these findings mean for people with MS, but we look forward to seeing the results of further research.
“In the meantime, we recommend that people follow government advice on maintaining a healthy, balanced diet, which includes guidelines on salt intake.”