Multiple Sclerosis and Sodium Toxicity: Controversy and Future Directions for Low-Salt Interventions

Salt intake is associated with multiple sclerosis; however, controversial findings that challenge this association rely primarily on methods that do not measure total sodium storage within the body, such as food surveys and urinary sodium excretion. In contrast, tissue sodium concentrations measured with sodium MRI confirm high sodium levels in multiple sclerosis, suggesting a role for sodium toxicity as a risk factor for the disease. Research on demyelination in the central nervous system has identified myelin phase transitions associated with increased salinity, which cause structural instabilities of myelin sheaths and add further evidence implicating sodium toxicity as a causative factor in multiple sclerosis. Inflammatory and immune responses in multiple sclerosis are also related to high sodium intake. In addition, salt is a potential mediating factor associating multiple sclerosis with comorbidities, including systemic lupus erythematosus, rheumatic arthritis, inflammatory bowel disease, and cardiovascular disease. Current confusion exists over classifying dietary sodium intake levels as low, normal, and high, and questions remain over levels of sodium restriction necessary for disease prevention. To reduce multiple sclerosis symptoms and prevent disease progression in patients, future research should investigate low-salt interventions with levels of sodium intake associated with ancestral hunter-gatherer tribes.