Harmful effects of excessive salt consumption: intestinal microbiota called into question
Excess salt decreases Lactobacillus content in the intestinal microbiota, thus promoting a pro-inflammatory state which is involved in the onset of disorders such as hypertension or autoimmune diseases.
Excessive salt consumption is involved in the pathogenesis of hypertension and could worsen the symptoms of autoimmune diseases such as multiple sclerosis, due to the increase in the number of pro-inflammatory cells, especially CD4 T cells, responsible for the production of interleukins 17 (Th17). Dietary salt intake variations have an impact on the composition of the intestinal microbiota and the regulation of T cell populations, including Th17. In order to shed light on the interactions between salt and microbiota and their potential clinical implications, researchers have carried out a study with experimental autoimmune encephalomyelitis-induced mice (a model for MS).
In these mice, a salt-rich diet led to a decrease in Lactobacillus (especially Lactobacillus murinus) in the intestinal flora. This imbalance disappeared after reducing the intake of sodium chloride. Moreover, this bacterial deficit is associated to an increase in the number of circulating Th17 cells. This link could be explained by the loss of indole-3-acetic acid as lactobacilli convert tryptophan into indole, which contributes to Th17 cell differentiation in vitro. Conversely, adding Lactobacillus to the salt-rich diet of these animals reduced the number of Th17 cells and limited blood pressure increase associated with the salt intake as well as autoimmune disease symptoms.
The link between salt, microbiota and inflammation was confirmed in a pilot study carried out in 12 healthy men who ingested 6 g of NaCl daily during 14 days in addition to the salt already present in their diet (equivalent to a double intake). The authors observed a decrease in all Lactobacillus populations, which became virtually undetectable (except for L. salivarus), as well as an increase in the number of Th17 cells and an increase in blood pressure.
These results suggest that probiotics could potentially limit the negative effects of an excessive salt consumption.
Wilck et al. Salt-responsive gut commensal modulates TH17 axis and disease. Nature. 2017 Nov 30;551(7682):585-589.