The role of dietary sodium in autoimmune diseases: The salty truth.

Autoimmune diseases are a group of heterogeneous condition that occur secondary to the intrinsic loss of tolerance to self- antigens. In genetically susceptible individuals, the complex interplay of environmental factors and epigenetic deregulations have been proposed to drive disease etiopathogenesis. Various environmental variables have been identified including viral infections, exposure to pollutants, stress and dietary factors. Sodium, a major constituent of salt is essential for mammalian physiology. However, high salt intake may play a role in the development of autoimmune diseases. Several lines of evidence point toward the role of high sodium intake in reversing the suppressive effects of Regulatory T cells (Tregs) and instead promoting cellular shift toward T-helper (Th)-1 and Th17 pro-inflammatory phenotypes. These effects have been attributed to cascade of events that ultimately results in downstream activation of serum glucocorticoid kinase 1 (Sgk1). In vivo, various autoimmune animal models have confirmed the role of high sodium diet in the emergence and the exacerbation of autoimmune conditions including for instance Experimental Autoimmune Encephalomyelitis model for multiple sclerosis, MRL/lpr mouse model for lupus nephritis, collagen induced arthritis model for rheumatoid arthritis, and dextran sulfate sodium induced colitis, and TNBS-induced colitis models for Crohn's disease. Clinical epidemiological studies are scarce. High sodium intake was associated with increased risk of rheumatoid arthritis disease emergence. In multiple sclerosis, some studies suggest a relation to clinical exacerbation rates however other studies did not corroborate these results. Taken together, high dietary salt intake plays a role in the spectrum of autoimmune disease etiology. Further research is warranted to better characterize such relationship and assist in identifying individuals that would benefit from dietary salt restriction.