Definition:

• Sodium and chloride — major electrolytes of the fluid compartment outside of cells (i.e., extracellular) — work together to control extracellular volume and blood pressure. Disturbances in sodium concentrations in the extracellular fluid are associated with disorders of water balance.
• Various mechanisms act on the kidney to ensure that the amount of sodium lost via renal excretion compensates adequately for the amount of sodium consumed, thereby maintaining sodium homeostasis.
• Hyponatremia (abnormally low sodium concentrations in blood) is common among older adults and in individuals with hypertension, kidney disease, and heart disease. Hyponatremia also occurs in up to 30% of hospitalized patients.
• Acute severe hyponatremia may lead to brain edema with neurologic consequences and be lethal if not promptly diagnosed and treated. Mild chronic hyponatremia with long-term adverse health effects, such as attention deficits, gait instability, falls, and bone loss and fractures, has been associated with cardiovascular morbidity and mortality.
• The National Academy of Medicine established a Chronic Disease Risk Reduction Intake (CDRR) for sodium of 2.3 g/day (5.8 g/day of salt) for adults based on evidence of potential long-term health benefits on blood pressure and risk of hypertension and cardiovascular disease associated with reducing sodium intakes below this level. 
• Current sodium intakes of the US adult population far exceed the CDRR. Sodium has been identified as a nutrient of public health concern for overconsumption.
• Excess dietary sodium is a major contributor to hypertension, which is a leading preventable risk factor for cardiovascular disease. Randomized controlled studies demonstrated that dietary sodium reduction (by 1.8 to 3.2 g/day) could lower blood pressure in subjects with elevated blood pressure. Yet, current evidence fails to support a decrease in cardiovascular morbidity and mortality with moderate sodium restriction in patients with hypertension.
• Additional adverse health outcomes, including gastric cancer, osteoporosis, and kidney stones, have also been linked to sodium overconsumption.
• High potassium intake increases urinary sodium excretion and appears to protect against the hypertensive effect of sodium. In addition, the administration of sodium chloride to people performing physical labor under conditions of high heat and humidity may exacerbate potassium depletion and worsen problems associated with heat injury. For these individuals, it has been suggested that sodium chloride supplementation should be less vigorous and should be accompanied by potassium supplementation.