Blackmores Institute

The study found that a high salt diet (HSD) has systemic immunosuppressive effects that negatively affects the anti-bacterial immune defence – an effect arising as a direct consequence of the physiologic hormonal response that initiates the excretion of excess sodium.Bacterial infections of the urinary tract are among the most prevalent infections and affect more than 25 percent of the population, especially young females. Uropathogenic Escherichia coli (UPEC) cause more than 70 percent of urinary tract infections (UTIs) and UPEC ascension from the bladder into the kidney leads to pyelonephritis, a potentially life-threatening disease,” the authors explained.“The innate immune defence against UTIs relies on neutrophilic granulocytes, which clear UPEC by phagocytosis, and on mononuclear phagocytes such as macrophages or dendritic cells, which attract and activate the neutrophils by chemokines and cytokines. Treatment of pyelonephritis includes antibiotic drugs and high liquid intake to flush UPEC out of the kidney. In the present study, we tested whether an HSD can strengthen the intra-renal immune defence against pyelonephritis.”After first establishing parameters for the study using mice where the researchers evaluated the influence of a HSD on immune response during bacterial infection of the kidney, the investigators sought to corroborate their findings with epidemiological data in humans.“There are no publications examining a potential association between salt intake and urinary tract infection (UTI) risk in humans, therefore we performed a clinical study with healthy volunteers, who consumed additional 6 g of sodium per day for one week - an amount is equivalent to 1.5 to 2 large fast food hamburger meals. After this one-week period on HSD, the salt concentration in urine increased and blood aldosterone decreased as expected,” the researchers reported.“We demonstrated that an HSD does not strengthen neutrophil responses but entails hormonal and metabolic alterations that systemically compromise their antibacterial activity. Hence, the recent proposition that the intra-renal sodium gradient establishes a defence zone against pyelonephritis must not be misinterpreted as implying that an HSD will support the defence against pyelonephritis. Instead, such a diet may be harmful in bacterial infections of the urinary tract and in other organs that do not accumulate sodium.”The study concluded that further clinical studies in patients with UTIs are required in order to test the findings of its experimental observations given that the high salt content of the Western diet is not exclusively pro-inflammatory but has immunosuppressive consequences that may be relevant to discussions on the recommended daily sodium intake.Source:
 Sci Transl Med. 2020. DOI: <a href="https://stm.sciencemag.org/content/12/536/eaay3850">10.1126/scitranslmed.aay3850</a>

A high salt diet may play a role in prolonged bacterial infections, a new study reports.

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