High-salt diet impacts health of the gut microbiome

A study published in the journal Hypertension suggests reducing salt intake can benefit the gut microbiome and blood pressure in women with untreated hypertension.

In the randomized, placebo-controlled study, the researchers examined the blood of 145 adults aged 30–75 with untreated high blood pressure who were enrolled in a previous study at the Queen Mary University of London. Because stool samples were not taken on the study participants, the researchers couldn’t look more directly at the gut microbiota, so instead measured circulating short-chain fatty acids (SCFAs), the primary metabolite produced by gut microbiota.

SCFAs are known to play a role in blood pressure regulation. These small metabolites originating from the gut get absorbed into the entire circulation, binding to receptors on the lining of blood vessels and in the kidneys, regulating things like the release of renin, an enzyme that works to keep the kidneys well perfused and a major player in blood pressure control. Blood levels of SCFAs can be considered an indicator of the health of the gut microbiome.

All the study participants were given two weeks of detailed instruction by nurses on how to lower their sodium intake to about 2,000 mg daily, information that was reinforced throughout the study. Half of the participants received either a sodium tablet or placebo tablet nine times daily for six weeks, then switched groups.

According to study author Haidong Zhu, a molecular geneticist at the Georgia Prevention Institute at the Medical College of Georgia at Augusta University, there is increasing evidence that the microbiome has a direct role in regulating blood pressure and how the average American high-salt diet can interfere with a healthy direction. The researchers’ hypothesis was that even a modest reduction in salt intake would alter concentrations of circulating SCFAs and lower blood pressure.

The researchers found that just six weeks of a daily sodium intake close to the 2,300 mg recommended by groups like the American Heart Association, resulted in increased levels of all eight of the SCFAs. The increased SCFA levels were consistently associated with lower blood pressure and enhanced blood vessel flexibility.

“Sodium is a factor in both sexes, but the impact in relation to the gut microbiome seems more in females,” said Zhu in a press release. “We need to study it further to see if that is true and why it’s true if it holds.” It may be that a high-salt diet affects blood pressure through different pathways in males and females, she added.