Here at Medical News Today, we have reported on studies showing that too much salt can double your chances of heart failure, and that even a low intake of salt may still put you at risk of adverse cardiovascular events.
But new research adds another key element to this dynamic: gut bacteria. Researchers from the Massachusetts Institute of Technology (MIT) in Cambridge, MA — together with researchers from various institutions in Germany — examined the effect of a high-salt diet on certain healthful gut bacteria.
Nicola Wilck, of the Max-Delbruck Center for Molecular Medicine in Berlin, is the first author of the study, and the findings were published in the journal Nature.
Dominik Muller, also of the Max-Delbruck Center for Molecular Medicine, and Ralf Linker, of Friedrich-Alexander University in Erlangen, Germany, jointly led the investigation.
Studying salt, gut bacteria, and hypertension
Muller and colleagues fed two groups of mice a diet high in sodium and a normal diet, respectively, over a period of 14 days.
Up to 4 percent of the former diet consisted of sodium chloride — which is what we have as table salt — while only 0.5 percent of the normal diet consisted of sodium chloride.
A fecal analysis revealed that high-sodium mice lacked a beneficial bacterium called Lactobacillus murinus. Additionally, the mice had more of the so-called Th-17 cells, a pro-inflammatory type of "T helper cells."
T helper cells are part of our immune system and they help create a pro- or anti- inflammatory response to a foreign agent in our body. They are called "helper" cells because they help other cells elicit an immune response.
Finally, in the experiment described in the study, the rodents that had been fed a diet high in sodium also had high blood pressure, or hypertension.
Significantly, when the hypertensive rodents were administered doses of a probiotic containing Lactobacillus bacteria, the pro-inflammatory T helper cells decreased, as did the mice's blood pressure.
To investigate further, the researchers conducted a pilot study in humans, in which they added 6,000 daily milligrams of sodium chloride in the diet of 12 individuals for a period of 2 weeks.
Probiotics may reverse salt's harmful effects
Muller and colleagues found that adding salt created the same changes in humans as it did in mice: high blood pressure, a high number of Th-17 cells, and lower numbers of the helpful Lactobacillus bacteria.
Interestingly, however, when people consumed a commonly available probiotic for a week before starting their high-sodium diet, both their blood pressure and the Lactobacillus levels remained within normal limits.
While the effects of too much salt on Th-17 cells have been shown in previous research — also conducted by Muller — and this new study brings this knowledge further, the exact mechanism by which these immune cells drive hypertension have yet to be unveiled.
On this, study co-author Eric Alm, director of MIT's Center for Microbiome Informatics and Therapeutics, comments, "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," he says. However, Alm notes, "If you can find that smoking gun and uncover the complete molecular details of what's going on, you may make it more likely that people adhere to a healthy diet."
The study's co-author also advises that the findings be taken with, well, a grain of salt:
"I think certainly there's some promise in developing probiotics that could be targeted to possibly fixing some of the effects of a high-salt diet, but people shouldn't think they can eat fast food and then pop a probiotic, and it will be canceled out."