Gut bacteria could be the link between salt and high blood pressure

A new study has found that a high-salt diet reduced Lactobacillus bacteria in the guts of mice and increased production of immune cells linked to high blood pressure. A pilot study in humans found similar results. But when the salty mice had their guts replenished with the lost bacteria, the effects were reversed.

The researchers showed “a diet high in salt, typical of Western countries and long implicated in hypertension, also affects the spectrum of bacterial species in the gut – the gut microbiome,” Professor Emeritus Brian J. Morris of the University of Sydney told the Australian Science Media Centre.

Lactobacillus, the type of bacteria studied, includes “good bacteria”, explained Hannah Wardill of the South Australian Health and Medical Research Institute and the University of Adelaide.

A high-salt diet increased the numbers of a type of immune cell that promotes inflammation, explained Dr Francine Marques of the National Heart Foundation and Baker Heart & Diabetes Institute. This increased inflammation in blood vessels, and blood pressure went up.

“These same cells had been previously implicated in the development of hypertension,” Marques continued.

She pointed out the researchers didn’t suggest a chain of events at the molecular level to explain the link between salt, the bacteria, and the immune cells, but hopes other studies will address this.

Importantly, the authors were able to produce a “very small (but significant) reduction” in blood pressure when the mice were given the depleted bacteria, Marques explained.

A smaller study was also done on humans.

Eight people “that received salt tablets on top of their normal diet for 14 days [had] an increase in blood pressure (as expected) and a decrease in [the immune cells],” explained Marques.

The researchers also looked at the amount of Lactobacillus species in the people’s faecal samples. According to Marques, they found most of the species had been lost at the end of the salt challenge in the subjects that originally had Lactobacillus.

“People with a healthy, traditional diet have high Lactobacillus in their gut, but the high salt diet of people in more affluent countries probably explains why they have low Lactobacillus levels and an epidemic of hypertension, as well as various autoimmune diseases,” warned Morris.

“Taking probiotics rich in Lactobacillus can lower blood pressure in people with hypertension,” he added.

“Lactobacillus can be found in several foodstuffs, including yogurt and some types of cheese,” explained Marques, “and some strains help us digest lactose present in milk.”

Although we are still in our “baby steps” in understanding the role of gut bacteria in complex diseases, Marques said this research “adds to this important puzzle”.

“[It] is the first to suggest that gut bacteria might act as the middle-man between salt and heart health, and provides a new therapeutic target to counteract salt-sensitive diseases,” added Wardill.

“Large, well-controlled, randomised clinical trials are now warranted to test whether boosting Lactobacillus can help stem the tide of rampant hypertension in our society,” explained Morris.

“But of course, if governments took the advice of health authorities and legislated against high salt and junk food generally … we would see a reduction in not only hypertension but the scourge of obesity, diabetes, many cancers and cardiovascular diseases generally,” he concluded.

Prepared by the Australian Science Media Centre and used here with permission.