A new study finds another reason to cut down on the salt: Increased salt intake may trigger and sustain some autoimmune diseases.
Autoimmune diseases are illnesses that cause the immune system to attack healthy cells instead of pathogens and can affect any part of the body. This includes everything from Type 1 diabetes, psoriasis, multiple sclerosis and rheumatoid arthritis. According to the U.S. Department of Health and Human Services Office on Women's Health, there are more than 80 different types of autoimmune diseases that affect 23.5 million Americans.
Autoimmune diseases have been associated with an overproduction of TH17 immune cells, a type of helper T cell (or white blood cell) that produces an inflammatory protein called interleukin-17, but science hasn't been able to determine why some people produce more TH17 than others, Nature pointed out. But, three separate studies published in Nature on Mar. 6 may provide more clues.
Researchers note that autoimmune diseases have gone up in the Western world, and many scientists believe it is because of environmental factors especially changes in lifestyle and dietary habits. More consumption of highly processed food and fast food have been pointed out as possible causes.
The first study used technology developed by Hongkun Park, a physicist at Harvard University in Cambridge, Mass. Silicone nanowires (or minute structures made out of silicone) were used to change genes inside an immune cell without changing how the cell functioned. This was able to provide a model of how TH17 cells worked. Co-author Aviv Regev, a biologist at the Massachusetts Institute of Technology, said to Nature that this work was necessary because the scientists would have been "guessing in the dark" trying to figure out how the TH17 cells were controlled.
Researchers in the second study then watched immune cells being produced over a 72-hour time period. Serum glucocorticoid kinase 1 (SGK1) -- which regulates salt levels in other kinds of cells -- was observed every time a TH17 cell was created. Researchers then discovered that mouse cells created in high-salt conditions had more SGK1 expressions and more TH17 cells compared to those in a normal environment.
"If you incrementally increase salt, you get generation after generation of these TH17 cells," study co-author Vijay Kuchroo, an immunologist at Brigham and Women's Hospital in Boston, Massachusetts, said to Nature.
The third study then built on the findings from the other two studies. Mice were placed on a high-salt diet and were observed creating more TH17 cells. The mice ended up having a severe form of multiple sclerosis called autoimmune encephalomyelitis.
"It's very clear in experimental models in animals that there's a dramatic effect going from low salt to high salt," author David Hafler, chairman of the department of neurology at Yale School of Medicine in New Haven, Conn., told Bloomberg.
Together the studies suggest that salt may spur the enzymes to create TH17 cells.
"We think of helper T-cells as sort of the orchestra leaders, helping the immune system know what the cells should be doing in response to different microbial pathogens," Dr. John O'Shea, director of intramural research at the U.S. National Institute of Arthritis and Musculoskeletal and Skin Diseases, in Bethesda, Md, said to HealthDay. He was not involved in the studies. "The strength of these papers is that they have found another factor that drives [helper T-cell] differentiation -- salt."
However, Hafler pointed out to HealthDay that salt may not be the only trigger since other genetic and environmental factors also play a role in autoimmune diseases. But, it does open the possibility that low-salt diets may benefit people with autoimmune disorders.
"They have now identified a biomarker, so you could treat people with a low-salt diet and then check for the marker in cells using cell cytometry, for example," O'Shea explained.