Researchers deem salt as risk factor for autoimmune disease

When tired, hungry and cramming for a big exam, it is easy to reach for a cheap and quick snack, such as some greasy and sodium-loaded junk food.

However, the next time you go to grab a bag of potato chips for a late night study session, you may want to think again. A new study examines the effects of salt consumption, hinting that those late night snacks may be even more harmful than once thought.

The study — which was released March 6 and a combined effort of the Broad Institute’s Klarman Cell Observatory, Brigham and Women’s Hospital, Harvard University, Massachussets Institute of Technology and Yale University — focused on an immune cell called “T helper 17” and its role in the immune system.

In looking at these Th17 cells and a regulatory gene called SGK1, researchers hypothesized that salt is a risk factor for the development of autoimmune diseases.

The immune system

The immune system works to protect the body by fighting foreign invaders, such as disease and infection, according to MedlinePlus Medical Encyclopedia.

In this system a balancing act exists, whereas either too much or too little activity can be harmful to the body. An imbalance can lead to the development of autoimmune disease, which occurs when the immune system attacks its healthy cells instead of protecting the body.

Researchers of the study examined the Th17 cell in particular, an immune cell that is vital for clearing foreign pathogens and that plays a role in autoimmune disease, especially in multiple sclerosis and psoriasis. While there are some “good” Th17 cells, there are also “bad” ones, according to a Research Gate publication.

The study investigated the causes of the “bad” Th17 cell, also known as the “pro-inflammatory” cell. Hans Dooms, a professor of medicine at Boston University, said these cells often lead to autoimmune disease.

The study

Researchers found two networks that regulate Th17 cells, one that causes the cells to increase in number and one that causes them to decrease in number. During the investigation, the SGK1 gene, which is important in Th17 development, stood out to researchers. This gene is also found in cells in the gut and kidney where it aids in salt absorption, according to the study.

Researchers then studied the possible link between salt and autoimmune disease. Using a mouse model of multiple sclerosis, the researchers discovered that the disease worsened in genetically predisposed mice when exposed to salt.

Ian Rifkin, a BU professor of medicine, explained this link between salt and the Th17 cell.

“What the researchers showed is that if you have an increased salt concentration, it can lead to an increased production of the Th17 cell,” Rifkin said.

Because researchers focused on the pro-inflammatory Th17 cell, the increased production of this cell became a direct path to autoimmune disease.

Some mice in the study were also injected with self-antigen an antigen of their own cells — for their immune system to respond to a high-salt diet. An antigen, according to the MedlinePlus Medical Encyclopedia, is any substance that causes your immune system to create antibodies against it.

With this injection, the T cells were activated and began destroying parts of the nervous system. This, according to the study, meant the autoimmune disease had been induced at a high rate.

This step of the research determined that high salt intake is dangerous to people genetically predisposed to autoimmune disease.

However, researchers in the study said their hypothesis must be tested with epidemiological studies on humans in the future.

Other causes of disease

Both Dooms and Rifkin said other factors could also contribute to the development of autoimmune disease.

“Autoimmune diseases are complex,” Dooms said, “We do not know if what we see here will hold up when the other cell types are in the picture.” He said this is why he and some researchers are wary of the study’s results.

Like Dooms, Rifkin said the disease’s development is complex.

“Most autoimmune diseases are the result of complex interactions between genetic and environmental factors,” he said.

Dooms said science has gravitated towards this idea — that disease is caused by the right combination of both genetic and environmental factors. He said the study examined this process because salt alone did not cause the autoimmune disease in mice.

College of Arts and Sciences junior Karissa Parker said she’s also wary of the results.

“I feel like you can’t just trust one study,” Parker said. “There has to be more than one, and it has to be proved consecutively before you can agree with it.”

An interesting connection

Autoimmune disease is becoming increasingly prevalent in the United States. The National Institutes of Health estimated that as many as 23.5 million Americans currently suffer from autoimmune disease, and this number is climbing.

The severity is not only in the number of cases. Autoimmune disease is becoming economically dangerous in terms of the country’s healthcare. The annual cost to treat patients with type 1 diabetes was estimated to be between $4.6 billion and $9.2 billion, and multiple sclerosis was estimated at $2.5 billion.

Autoimmune disease is most common in westernized, highly developed regions of the world, Dooms explained, so it may be related to lifestyle. He added that the number of cases of autoimmune disease is much lower in developing countries.

“In less developed countries you see more occurrences of infection. The immune system may be too busy fighting parasites to find a chance to develop these kinds of cells that fight the body,” Dooms said.

Other reactions

A number of BU students said they were not surprised by the connection between salt and autoimmune disease, but differed in their prescribed responses to the results.

Parker, although circumspect of the results, said the study will make her more aware of the risks of excessive salt consumption. However, she said she doesn’t plan to cut salt out of her diet.

“I think it’s about proportion,” she said. “A little bit of salt is not going to kill you. It’s all portions.”

Sargent College of Health and Rehabilitation Sciences senior Sofia Pevzner said she considers herself a healthy eater, generally avoiding snacking on salty foods. However, she said this behavior is the not likely the norm for a college student, whose stress often causes food cravings.

“When people are under stress, they just eat comfort food,” Pevzner said. “Generally, comfort food is not healthy food.”

CAS sophomore Yi Man Cheung also said she is a healthy eater and agrees with Pevzner in terms of the average student’s diet.

“College students find the most convenient and tastiest food,” Cheung said.

She said this is because students have tight cash budgets and a lack time.

The future

It is important to think about what the implication of this study is for human disease and the role of diet in human disease, although it may be too early to reach a significant determination, Rifkin said.

“I do not think it is enough to make certain dietary regulations for autoimmune disease,” Rifkin said. “It is a study that suggests we should be doing studies in patients with disease.”

Dooms said researchers could use this study for therapy in the future. Using study patients in a clinical setting, researchers could look at possible therapeutic effects of a low-salt diet.

He also said low-salt diets could lower the number of bad Th17 cells and help avoid autoimmune disease. This, however, can become difficult because our body still needs some Th17 cells.

“We need to be cautious since a low-salt diet may also lower the number of ‘good’ Th17 cells and make patients more vulnerable to disease,” Dooms said.

However, Dooms said everything turns back to the idea of balance in the immune system, which needs to stimulate the T cells that protect the body while avoiding the pathogenic ones.

“It may be possible to find a diet with just the right amount of salt to accomplish this,” he said. “It is also likely that this ‘ideal’ amount will differ from person to person.”