Two new studies add to a growing pile of evidence that a salt-heavy diet can spur the development or worsening of autoimmune diseases. These ailments, which include multiple sclerosis, type 1 diabetes, inflammatory bowel disease, and psoriasis, result from an immune system gone haywire that attacks the body instead of germs.
Medical investigators have long searched for environmental triggers to explain the spike in many such diseases over the last half-century in Western countries. The too-much-salt hypothesis is an attractive one, given the simultaneous rise in the popularity of processed and other "fast" foods which, as we all know, often come loaded with sodium. The evidence is fast becoming clear that there is some connection between salt and these disorders.
The studies, both published in 'Nature,' looked at how cultured cells behaved when exposed to salt concentrations mimicking a salty diet. They made an excessive amount of a cell type called a helper T cell, one that cranks out the inflammatory protein interleukin-17 (Il-17). These so-called Th17 cells are known to be major drivers of autoimmune disease. In examining mice fed a salty diet, the researchers saw that the rodents likewise produced more Th17. A subset of these mice genetically altered to be prone to an autoimmune disorder similar to human multiple sclerosis also developed a more severe form of the disease.
There is plenty of pushback to the studies. These initial findings are controversial because of their wide-ranging implications – for fast food establishments and public health – and should open up a flurry of follow-up investigations that assess salt-rich diets and autoimmune disease rates. Until then, it's best to watch your salt intake. "We know that it's important for health for a number of reasons to have a moderate intake of salt," says John O'Shea, scientific director of the National Institute of Arthritis and Musculoskeletal and Skin Diseases Intramural Research Program. "Most people should be paying attention to that anyway."
Yet applying truly low-salt diets – above 1,500 mg but below 3,000 mg – is a challenge for most Americans, and even in clinical trials, given Westerners' by-now ingrained love of salt. "Everybody cheats on their diet," said O'Shea. "These are hard trials to do."