High-Salt Diet Kills Beneficial Gut Bacteria, Leading to Disease

A team of international researchers has found a high-salt diet reduces the population of the beneficial gut bacteria Lactobacillus. This, in turn, impacts immune cells which can lead to the development of hypertension and autoimmune disease. Probiotics may help to curb these effects.

Gut Flora and Salt-Sensitive Diseases

A high-salt diet has long been identified as a contributing factor to high blood pressure, stroke, heart disease and heart failure. When salt accumulates in the bloodstream, the body retains fluid in order to dilute the sodium. The heart and blood vessels then have to work harder to deal with the excess water, which causes the blood vessels to stiffen and can lead to cardiovascular complications and potentially death.

Higher intake of salt has also been linked to the development of stomach cancer, and it may further exacerbate osteoporosis symptoms. Previous research has shown that reducing salt intake both lowers your risk for cardiovascular disease and related deaths over the long term, but scientists are still trying to understand the mechanisms underlying these connections.

Imbalances in the gut’s microbiota have been implicated as underlying factors in systemic inflammatory conditions and immune system disruptions. Research has shown that gut bacterial imbalance may be involved in many of the same cardiovascular health problems that arise from a high-salt diet. "But so far, nobody had studied how salt affects the bacteria in the gut," said the lead researcher of the study, Professor Dominik Müller of the Experimental and Clinical Research Center (ECRC) and Max Delbrück Center for Molecular Medicine in Berlin, Germany.

Müller and his colleagues felt that this was a deserving point of focus. According to fellow team member and ECRC researcher Dr. Nicola Wilck, “gut bacteria influence the host organism, and the immune system is also very active in the gut.” The team decided to investigate the effect that salt has on the bacterial populations of the gut to determine what changes occur and discern if those changes may be linked to the detrimental effects of a salt-laden diet. The team’s research has been published in the journal Nature. Their findings were recently presented at the British Cardiovascular Society Conference in Manchester in the United Kingdom.

High-Salt Diet Kills Off Lactobacillus Populations

With their research, Müller and his team have successfully demonstrated that excess sodium decreases the Lactobacilli in our guts while raising blood pressure and increasing the number of Th17 helper cells, immune cells that stimulate inflammation, cause hypertension and are associated with autoimmune diseases such as multiple sclerosis. According to Müller, “we should start to see our gut microbiome as a viable target for treating conditions that we know are aggravated by salt, such as high blood pressure and inflammation.”

In their experimentation, the team fed mice a high-salt diet in which sodium made up 4 percent of their daily intake, compared to the 0.5 percent sodium intake of a normal diet. The team found that the higher salt intake led to a decline in the population of Lactobacillus murinus bacteria. Mice fed this diet had higher blood pressure and were also found to have increased populations of the Th-17 cells. When the mice with high blood pressure were given a probiotic which contained Lactobacillus murinus, Th-17 populations declined and the symptoms of hypertension decreased.

The researchers then decided to investigate if this effect would carry over to human subjects. The team investigated the gut microbiota of 12 healthy men who were administered six additional grams of salt, roughly doubling their sodium intake, every day over the course of two weeks. As was observed with the mice, within human test subjects, lactobacilli were sensitive to salt intake, becoming almost undetectable after 14 days. As expected, participants’ possessed higher blood pressure and an increase in the number of Th-17 helper cells in their blood. Participants who took an over-the-counter probiotic for a week prior to starting the high-salt diet retained normal blood pressure levels, and their Lactobacillus populations remained intact.

A Window Into Future Therapies

According to the researchers, “it is still unclear exactly how Th-17 cells contribute to the development of high blood pressure and other ill effects of a high-salt diet,” but they are hopeful their research will help shed light on potential treatments for salt-sensitive illnesses.

Fellow researcher, Dr. Ralf Linker from the Friedrich-Alexander University said, “multiple sclerosis may be one of the salt-sensitive diseases which we might be able to treat in the future with individually-tailored probiotics as add-on to standard immune therapies."

While the role gut microbiota plays in our health is increasingly an important focus of research attention, there is much we still don’t know about how other organisms impact and interact with our gut flora. "Our study goes beyond just describing the changes caused by salt. We want to consider interrelated processes," said Dr. Müller. "We can't exclude the possibility that there are other salt-sensitive bacteria that are just as important as Lactobacillus," he continued. "This could be the tip of the iceberg in targeting gut bacteria for treating serious illnesses."

“We’re learning that the immune system exerts a lot of control on the body, above and beyond what we generally think of as immunity. The mechanisms by which it exerts that control are still being unraveled,” said team member Professor Eric Alm of MIT. “We hope that our findings, along with future studies, will help to shed more light on the mechanism by which a high-salt diet influences disease.”